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Introduction This is a program for manipulating bitmap images. Users of Windows will already be familiar many such programs. The special features of DPScan are;  I It can work with 1, 2, 4, 8, 16, 24 and 32 bits per pixel images directly. Often other programs require images to be changed to another format before they can be edited.  I Various RISC OS file types are supported.  IIt is also available for RISC OS and so will be familiar to RISC OS users.  Fundamentals Images, or pictures come in two basic formats - bitmap or vector. A bitmap image consists of a huge number of coloured points. Usually these points will be referred to as pixels or dots. The dots are arranged in a rectangular array, the size of an image can then be specified by the width in pixels and the height in lines or rows of pixels. The principle is the same as TV pictures. Vector images consist of lines and curves which specify filled areas. For Windows the typical bitmap image is a Windows BMP file, and the typical vector image a Windows Meta File (WMF). Mostly this program is concerned with bitmaps. Given a bitmap image consisting of lots of pixels. Two fundamental numbers control how it will look. First the 'resolution' this is how close together the dots are. It should be obvious that the finer the dots, the better the image will look. To specify resolution, we talk about 'dots per inch' or 'dpi'. The resolution may be different across the image to down it. Therefore there is the X or horizontal (left to right) resolution and the Y or vertical (top to bottom) resolution. Second how many colours each dot may be displayed in. This is controlled by the number of bits used to store each pixel. If one bit is used for each pixel, then the pixel can be in one of just two states, on or off. If 2 bits are used for each pixel, it can be one of four colours. Four bits per pixel give 16 colours and 8 bits 256 colours. No mention has been made of how the states of these bits relate to the colour seen. For example in the one bit per pixel case, the on state might mean a black pixel or a white one with off meaning white or black. Conventionally a table is provided with the image that links the state of the bits with the real colours displayed on screen. This table is called the 'palette'. We shorten bits per pixel to bpp or sometimes 'bits' in future. For more than 8bpp, the palette would be too big, so for images with a larger number of bits, a different method is used, with the bits representing the colours directly. For a 16bpp image 5 bits are allocated to each of the colours red, green and blue (RGB), for 24 and 32 bits, 8 bits are allocated. As expected the more bits per pixel, the better images will look. However they will use more memory. Most Windows users have their screens configured to 96dpi horizontally, and vertically. In Windows terminology this corresponds to small fonts. The usual alternative is large fonts or 120dpi. More recent versions of Windows allow any screen resolution to be used. Normally the Windows screen uses 24bpp, older computers may use 15 or 16bpp or even less. Dot matrix printer or Fax machine output is typically 200 dpi, laser printer or ink-jet output is 300 or 600 dpi. Books are typically printed at 2400 dpi. It is possible for some pixels to be transparent. If pixels are completely transparent or completely opaque, it is common to say the bitmap image has a mask, or is masked. If the transparency is variable the image is said to have an alpha channel. Various methods can be used to support transparency, one way is to store another array of values which hold the transparency value for each pixel. Another technique is to specify that any pixel of a certain colour is transparent. Images may be defined in various colour spaces. The common one is RGB (red, green, blue) used by all computer screens. Another is CMYK (Cyan Magenta Yellow blacK) used in printed material. It is common to see scanners advertised as "1200 dpi, 24bit colour". The inclination is therefore to scan everything at the maximum resolution and in as many colours as possible. However consider scanning a page of A4 at this resolution. The resulting data would occupy some (1200x1200x10x12x24)/8 bytes, about 480Mbytes. This is larger than the memory on many computers, and would make the image difficult to handle. The lesson here is to use resolution sparingly. Often using lower resolution will not give visibly worse results. There is usually nothing to be gained by scanning at a resolution higher than the optical resolution of the scanner, this is the actual resolution of the sensor and mechanism of the scanner. Most scanners offer to produce higher resolution images but do this by inventing extra data.s trans P NrYqP NCY@7P N;Y@< NÜY@tn$ETB5rx?#@% (rx.#@W <$ECTBb$En?TB;p NGY6U D NY@.< N4BY@XD NԃY@mPD NtńY@M@ NY@  NgY@( NY@< N4Y@ N,Y@$ NY@5, NTφY@LT NY@jX NRY@dLH N4Y@qP NՇY@) N6Y@V0 NTxY@]T NY@/8L NY@ ~T N4=Y@98 NY@V8 N߉Y@]D NT!Y@@A@ NbY@P< NY@/ NtY@8 NSrY@{H NY@;D NY@0 N37Y@|X NY@gV< NفY@"X N:Y@CD0 N3|Y@O\@ NӽY@(H NsY@;x NS`Y@s  NY@KL NY@%H N3%Y@( NY@ , NDŽY@h4 NS Y@wD NJY@ |D NӫY@$ NsY@( N/Y@eL NY@<0 NцY@)A$ N3Y@ NtY@$ NY@\@ NSY@ $ N8Y@)  NzY@'D( N3Y@  NY@c < Ns?Y@s( NSY@H NY@ T N#Y@5, N3eY@o  ttL  LL P P b <P  x  D0X]7%n@n@))w  t%L  L% `m> `m> rx <`m>  x  ;0X]7n@n@))V  &?)EL A4PYF'G(J$x $ '2. Installation If you are using the program with a scanner, you will need to install TWAIN on your computer. You will also have to have some sort of physical connection between the scanner and the computer. Full details of this will be given in the documentation with your scanner.  Run the DPScan installer by double clicking on it. The installer is called dpscani.exe. The installer will prompt you for various pieces of information, the process should be familiar from other Window programs. Once installation is complete you can use the Windows Start menu to run DPScan. An empty DPScan window will appear. To the left of the main window a small window will open showing tools. Below the main window there will be another window which shows information about the current image. These are referred to as the toolbox' and 'info palette'. Different tools can be chosen by clicking on them. When a tool is chosen the info palette display will change. The main window is used to display images being manipulated, to set the area of pages to be scanned, and the position on the page of images being printed. The caret can be positioned in either the main window, or the info palette by clicking on the main window or in one of the writable icons in the info palette with the left mouse button. The Help menu (right hand side of the main window menu bar) has two entries, the first displays a help file which contains general information about the program. The second entry displays an information window. This will show you which version of the program you have. Please quote this in any correspondence. You can quit the program by closing all open windows or by using Exit on the File menu. e main (XXX NrYq WP NCY@pYL N;Y@, N}Y@dG@ N#Y@1 N Y@\ L NaY@xW< N‚Y@4 N#Y@  NeY@  NY@  NY@( NchY@EJD NY@yS, NY@8 NC-Y@H NnY@t NυY@P NcY@9#, NCrY@)8 N㳆Y@uT NY@ \ NcVY@wT NY@@ NهY@k4 NCY@M N\Y@_@ NýY@[D4 NcY@K, NC`Y@ ptHt)3L & L3 )P P b P  x  Y0X]7'(n@n@P )Q )XR P 8IP?T&BZL A4en[@\A  @3. Scanning something This is the process of getting an image from paper into your computer. We can only deal with the computer side of the process here. You must have connected the scanner to your computer, usually via the SCSI bus, USB port, or possibly the printer port. The object you want to scan must have been inserted into the scanner, and the scanner switched on and made ready. Full details of this process should come in the documentation for the scanner. The program controls scanners via a software interface called TWAIN. Before trying to scan anything, you must have installed TWAIN. You must have a suitable TWAIN driver for the scanner you want to use. Having completed the obvious steps above, this is a typical scanning session. First load DPScan from the start menu. Click on File on the menu bar. Choose 'Select Source...' This will open the TWAIN manager source selection dialogue box. Click on the name of the data source for your scanner, and then OK. Now repeat the process but this time, choose 'Acquire...' from the file menu. The window for the source for your scanner will open. Follow the instructions supplied with your scanner, eventually you will end up with an image in DPScan. To save your image again use the File menu. There are some keyboard short cuts to make the above process simpler. Shift F10 will open the TWAIN source selector, and if you only have one source installed, it is not necessary to go through this step. F10 will open the source window i.e. the same as Acquire... Much of the rest of this manual is concerned with the things the program lets you do with images once you have scanned them, and various ways of making the above process easier or more accurate. 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N6qY6U He?$΀?@de?$#?@ e?$Q?@Xe?$c?@0e?$C?@ zApf W ttcsWnL T Ln qc`m> `m> rx `m>  x  z0X]7`UVn@n@{)|) } @XXo qem[ VW{yfmgO`5T$fmgO`5(e]_I JAWiw"WJXXq onfm(u,GfmiT$fmiTbl D pGJ tscL T h2`L sP P b P  x  0X]7nUVn@n@))X XX Y S}ekYmO#T$YmO#cS Quq@wQKXX YM S3}3eYPOy8T$YSOy8S4[ `yw1wSR Xt%X O|SFpBP>:SFT$P>:SF>,/3i\  phJXX ONBVpB&INBVT$&INBVldfl pXz " x"DrawArcDraw "8"snappwwwwwwUUUUUU333333DDUU                                                                              J<H X Y ,GY^iT$Y^iGIV K *%pPH  XX fm S}09Y O)T$Y O)Ƹ S  yK,s3|ttsL T L `m> `m> rx `m>  x  z0X]7UV   n@n@)D XX fms-K@xT@xm9s ] pF\tL T L P P b P  x  0X]7UVn@n@))| ttL T @L `m> `m> rx `m>  x  z0X]7UV !"#n@n@)m H$HtL T JLL P P b P  x  0X]7UV-./0n@n@E X Yc)#R2PVW<}T$PWW<}Ml p(PpFk  \ptL T LL `m> `m> rx `m>  x  z0X]7UV89:;n@n@)); X@X `mtbP44f_8`mtb\T$`mub\4dYX )q ';ppZ X =0sfd}?0T$?0n7T f ߄np_> TL A4 J$lJLL5. Edit This menu is the third entry on the main menu. It controls operations altering the physical aspects (e.g. size) of the current bitmap. Flip Horizontal This has a similar effect to reflecting the image in a mirror running from top to bottom. The points on the left of the image, move to the right and so on. Flip Vertical Similar to Flip Horizontal, but doing the reflection in a horizontal line. Rotate This allows the bitmap to be rotated. Rotations by 90 and 180 degrees can be done more efficiently, so extra buttons are provided for these. Other angles can be set in the writable icon, either by typing them in directly, or by using the arrows to step through the possible values. Clicking on OK will then carry out the rotation. Angles are measured anticlockwise - a positive angle represents a rotation anticlockwise. When a bitmap is rotated by an angle other than 90 or 180 degrees, it will cover a larger area - bitmaps must always be rectangular. The new area will be in the current background colour. This can be set from the palette window as described in chapter 7. You can Control drag with the pointer tool to nd angles if youre trying to make things horizontal or vertical, see chapter 4. Shear This pushes the bitmap over sideways. In other words it converts a rectangular shape into a parallelogram. Skew is another term for this effect. It is possible to shear in either the X or Y direction, by selecting the appropriate button on the dialogue box. Resize This allows you to change the size of an image. In general there are various ways to do this. Changing the size is equivalent to changing the resolution of the image. Simply because an image which is twice as wide will have twice as many points - as will one which has the same dimensions but twice the horizontal resolution. The dialogue box lets you specify the scaling in one of three ways. Either a percentage change - select Percent and the Size option. For example 200 will make the image twice as big. Secondly you can specify the new dimensions of the image - clear Percent and select Size. Finally you can give the image a new resolution - select Resolution. To use any of these options you first need to select the appropriate icons, and then type in the values you desire. Clicking on OK will start the scaling process. The text icons on the right hand side, show the old values for the parameters of the image. The two 'Memory' icons show how much memory the old image used, and how much the new one will. The Lock aspect button will when selected ensure that the image retains the same ratio between the X and Y dimensions. Although scaling is a common option in bitmap programs, usually it is done in a simple way. For example, if you want to make an image twice as tall, the obvious scheme is to just duplicate each row in the image. However a moments thought will show that this is not the best approach. Imagine that two neighbouring pixels have the values 1 and 3, a good guess would be that any pixel inserted between them should have the value 2 i.e. (1+3)/2 or the average. This sort of technique is called 'anti-aliasing'. It can be done in various ways. You can specify the 'filter' to be used from the General configuration dialogue box. The choice of filter will also alter the results of rotation and shear operations. See chapter 8. Antialiasing will give better results on images that support a wider range of intensity levels. It may well be better to convert your image to a larger number of bpp (see chapter 7) before you start processing it.  Crop This entry on the Edit menu, will reduce the size of the image to that part of it which overlaps the rectangular selection. Extend The Extend entry will make the image large enough to fill the rectangular selection. Undo The number of steps you can undo is set from the general configuration window. Redo Redoes anything undone. Copy Copy the current image to the Windows clipboard. Paste Paste the Windows clipboard contents into the current window. On Windows pressing the Print key copies the current screen to the clipboard, so Print followed by Paste is a quick way to do a screen snapshot. Similarly Alt+Print copies the active window to the clipboard.ll al DDD NrYqG0UCk@<U;k@:U}k@U܁kFB{PU k@[Uak@UCk@UnkFB5HUEk@FUck@XUkFB%,U)k@Ukk@ܰU#k@kOUk@pUc0k@Urk@eUk@{Uk@pU#Vk@Uk@WUk@RLUC:k@sXU{k@ƹUk@OU#k@,8U`k@ZUk@UCk@)&dUnBkFB(UÅk@vUcljk@!U k@Uik@Uk@NU#k@VE 8}Jp FBE,}J @}J @}J37 @D}Jx @Ԁ}Js @}J @!}J= @}JS @}J3 @҃}J! @}}Ja FB%1}J^ FB}J @ P}JG @7}J~ FB}JɄ FBt N)YFB8 NY@Y@ N3΅Y@}L NY@{D NsQY@ӡ, NY@$ NԆY@k4 N5Y@w@ N3wY@WD NӸY@4 NsY@nL N `m> rx `m>  x  0X]7 YZ[\n@n@ :<)Y = XX amrvI jn|!6T$n|!6taVZ<PJ 9M(#pVD:L A4 ,;#x# $$$x>>>6. Filter Filters allow you to modify an image depending on it's contents. For example using filters you can blur images or sharpen them. There are two main types of filters 'User filters' which can be set up and modified at will, and the filters which are built into the program. The filters are accessed from the fourth entry on the main menu. If there is a selected area, the filter will apply just to that, otherwise it will apply to the entire image.  Built in filters Invert This replaces pixels in the image by their inverse. Black becomes white, colours are replaced by their complements. Histogram This is slightly more than just a filter. When you select it a histogram of the image will be calculated. This shows the number of pixels in each of a number intensity levels or bands. The Red, Green and Blue buttons can be used to choose which components are displayed. You can change the number of levels with the writable icon at the top right and the associated up and down buttons. The 'Equalise' button will attempt to spread out the pixels in the image so that there are equal intensities in each band. Under the histogram, are two arrows which can be dragged from side to side. When Expand is clicked on, the range of intensities between the arrows will be expanded to fill the full range. Expand and Equalise are crude tools. They may be of use with images where all the pixel intensities have been squashed into a narrow band. Finally the 'Recalc' button can be used to recalculate the histogram if the image is changed. Right clicking over the histogram window or clicking on the Save Data button will open a standard Windows save window that will let you save the histogram data as a text file. This might be useful to analyse data in another program like a spreadsheet. Max This filter replaces each pixel by the maximum of itself and the surrounding 8 pixels. The maximum of 1,2,3,4,5 is 5 Min This filter replaces each pixel by the minimum of itself and the surrounding 8 pixels. The minimum of 1,2,3,4,5 is 1 Median This filter replaces each pixel by the median of itself and the surrounding 8 pixels. The median of a set of values is the value which splits the set into two equal parts. For example the median of 1,2,3,4,5 is 3. This filter is useful for removing noise from an image. Average This filter replaces each pixel by the average of itself and the surrounding 8 pixels. For example the average of 1,2,3,4,5 is (1+2+3+4+5)/5=3. Add Noise This adds random noise to the image. The amount of noise is controlled by the slider and writable icon at the top of the dialogue box. The button 'White noise' controls if equal amounts of noise will be added to the colour components of the image. If 'White noise' is selected, the image will retain its colour. If it is not selected the image will tend to develop coloured dots. Noise may be useful in making images look more life like. For example images which have been processed into a small number of brightness levels. By adding noise the obvious levels can be smoothed out slightly.  User Filters. Technically speaking all the user filters are 'convolution filters' - each pixel is replaced by a combination of the values of its neighbours and itself. The combination is a fixed set of numbers - unlike for the Maximum and other filters above. The coefficient of each pixel can be specified, along with a global scale factor and a shift. The user filter menu will always have as it first entry 'Edit...' Selecting this will open the Edit user filter window. Underneath this the names of all the filters that have been defined will appear. These filters work like the built in ones, clicking on the name applies the filter. User filters will apply to just the selected area of the image, or to all of it. Some of the user filters supplied are 'Sharpen' to make images look sharper, and 'Blur' (the opposite of sharpen) to make images more fuzzy. It can be useful to sharpen images before applying some of the colour dithering techniques described in Chapter 7. Edit user filter The centre position in the matrix of writable icons represents the current pixel, the other icons then represent its neighbours. Often only the central 3x3 area will be used. The bottom two icons show the overall scale and shift factors. Pixel intensities are always between 0 and 255. Clicking on the right pointing arrow at the top of the window will open a menu showing all the filters that are defined and by selecting one, you can change the filter displayed. The row of buttons along the bottom of the window allow you to carry out various operations on user filters. New This opens a window allowing you to enter the name of a new filter and the name of the filter to base it on. Rename This opens a window similar to New, but allowing you to change the name of the filter. Delete This deletes the current filter. Cancel Closes the Edit filter window, and leaves the current filter unchanged. OK Close the Edit filter window and saves the new filter definitions to disc. More technical users may wish to know that the filter definitions are kept in a text file called Resources.Filters. Some examples may make how to use these filters more clear. The first example is a filter that does nothing, it just leaves the image unaltered. nnnnnn0,0,0cnShift=0 nnnnnn0,1,0cnScale=1 nnnnnn0,0,0 Only the central 9 entries are shown, the rest should be 0. So for each pixel there will be one contribution from the current pixel and none from its neighbours. The output intensity will be the same as the input. Next a filter that inverts the image. nnnnnn0,0,0,TnShift=255 nnnnnn0,1,0,TnScale=-1 nnnnnn0,0,0 A filter that sharpens an image (Sharpen). nnnnnn-1,-1,-13-nShift=0 nnnnnn-1,10,-1,nScale=2 nnnnnn-1,-1,-1 note that the sum of the central pixels and its neighbours is (-8+10)/2=1. 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N>YFBT, N:Y@0 NYFBR N݂Y@+P NY@eT NS`Y@Vh N3Y@ N"Y@e NcY@Q, NĄY@R  N3Y@  NGY@x NY@8 NSY@~  N+Y@ NӌY@= NY@&  NS/Y@  NpY@x NчY@? N2Y@R  NStY@  NY@H NY@, NwY@kH NSY@dh N3Y@R  N[Y@  NsY@H NSY@c  M`tL  tL P P b P  x  0X]7defgn@n@ ) ) XX ; ylD>T$=  13^p5Jt\t L JLL `m> `m> rx `m>  x  0X]7,opqrn@n@)) X `m0$]S<nSh0 eT$nRh/ ec7`"u ap  DZt 1,L  LL, - P P b P  x  0X]79z{|}n@n@, . )/ XX- /,tU=%aT -.tH1, T$uI10 '0q   4GpHXX/ -YV 9_.t^T$t^bn 4 y p&V6z  t1 9L  4(L9 1`m> `m> rx `m>  x  0X]7,n@n@))S := L A4 ;<J$JJ$xS4=;<<<7. Colour Colour is the fourth entry on the main menu, as the name suggests it allows control of the colour of an image. This ranges from actually changing the colour to changing the number of bits used to represent it. Some of the colour options are very simple, others provide a lot of scope for experiment. As usual, the menu options will be dealt with in order.  Swop This allows you to interchange the red, green and blue components of the image. It may be of use if for some reason the components have been confused or for effects. This function can be applied to a selected area as well as the entire image. The first entry rotates the colours red becomes green, green blue and finally blue red. The other options swop two components.  Grey Scale This converts a colour image to black and white, or in general a series of shades of grey. The weights used to do this can be set from the General configuration dialogue box. See chapter 8. These weights define how bright a colour is perceived to be. Because the eye is more sensitive to green light, green is given a greater weight. If a non-paletted image (more than 8bpp) is grey scaled it will automatically be converted to 8bpp with a linear grey scale palette. This produces a useful saving in memory, and loses no quality. Throughout the program, there is special code to deal with grey scale images, although they are always stored as 8bpp images with a palette.  Change Format This is probably one of the most complex functions in the program. The basic problem is taking an image with one bpp value and convert it into another image with a different bpp value. If the bpp value of the final image is greater than that of the starting image then usually there is a perfect mapping. The final image will look the same as the source image. Problems arise when the conversion is in the opposite direction from a larger bpp to a smaller one. There is also a case of converting between the same bpp but with a different set of colours in the source and destination image palettes. Some examples may make this clearer. Many printing processes can only reproduce black or white dots (a 1bpp image) yet often one sees illustrations in shades of grey (perhaps 4 or 8bpp). This has been done for centuries by a technique called 'half-toning' (also called ordered dithering) which allows shades of grey to be represented by combinations of black and white dots. You may want a GIF file for a web site, such a file can only contain up to 8bpp yet images off your scanner may be 24bpp, or perhaps have colours in their palettes that do not correspond to those in the standard desktop palette. The familiar RISC OS program ChangeFSI manages to convert such images by a process called Floyd Steinberg integration. Colours are chosen so that on average they represent the colours in the original image. This is done by finding the closest colour to the current pixel, and then calculating an error. The error value is added to the value of the next pixel and the process repeated. This is the Change format window. The icons on the left show the bpp and palette type of the original image. Those on the right the corresponding values for the new image. You can step through the values on the right with the arrow icons. Three conversion methods are supported. None In this colours in the new image will simply be the ones closest to those in the old. This is sometimes called 'thresholding'. In the case of going from a grey scale image of 8bpp to a black and white image of 1bpp, pixels would always be black or white depending on if the value of the original was greater or less than a threshold value say 50%. Usually for realistic images this option is of little use, it may be more useful for getting 'posterised' effects. FS This is Floyd Steinberg dithering. It can give good results. Typically you would use this option to convert a 24bpp image that you had scanned and manipulated to 8bpp before saving it as a sprite for use in other programs or where it will be displayed on the desktop. Zig Zag controls how the images are scanned. When selected the scan will change from left to right and right to left on alternate lines. In general Zig Zag will give the best results. Simple controls how the error in the colour of one pixel is shared with its neighbours. When Simple is selected all the error is passed to the next pixel to be converted on the same line. This simple dithering is the same as is used for the main program display when 'Dither' on the tools palette is selected. When Simple is not selected, true Floyd Steinberg dithering is used, with the error being spread over both the next pixel, and neighbouring pixels on the next line. In general Simple not selected will give the best results. Using Simple may be useful if you want to get an image that is exactly the same as the one on screen. Exact. By default colours are found using a lookup table of nearest values - this has limited precision. If Exact is chosen, a search for the nearest value will be carried out for each point. Exact takes a lot longer to do the conversion, but can give the best results. Ordered This is traditional half-toning. Results can be almost as good as FS dithering, and are usually a lot faster. New bpp It is possible to choose any of 1,2, 4, 8, 16, 24 or 32 for the new images bpp. It is important to set this. There's little point changing to the same bpp, unless the palette is different. New palette This can take various values. RISC OS The RISC OS palette is defined as that used in the desktop by default. In 8bpp modes there are limitations on the possible palettes. This is the most common setting for the new palette, since usually images will be for display on the desktop. Optimal If this is selected, the image will be analysed and a palette created that represents it best. You use this if you want the best results, and are going to display the image on hardware that imposes no limitations on the palette. RGB This selects 'digital RGB' for the new palette. This means that the ranges of red, green and blue are split into equal parts. For example, in an 8bpp image, RGB can be given 5 levels each. This palette can be useful for producing images to be printed on printers that can reproduce red, green or blue dots with each dot being 100% on or off. Linear GS A linear grey scale palette. This can only be used on grey scale images. None This is used to indicate that the palette is the same as the original. However, when used in the old values icons, None indicates that the old image really does have no palette for example a 24bpp image. There is a folder called Palettes in the folder where DPScan is installed. RISC OS Palette files in this will appear as destination palette options in the Change Format window. One palette file suitable for Netscape is supplied. See the section on the colour palette for details of how to load and save Palette files.  Colour Balance This window, gives you a set of sliders that can be used to give global changes to the images colour. Changes can be applied to the entire image, or to a selected area. The four values that can be changed, are related to the HSV colour model. The best way of understanding this, is via the colour wheel displayed by the palette window, and described in a later section of this chapter. The concept of brightness should be intuitively obvious. The brightness slider makes all colours brighter or darker. The contrast slider has a similar effect, except brighter colours have their brightness level increased more than dimmer colours. Note that the values shown are of changes to the image. If you enter a 5% contrast increase, and click on OK, then to get back to the original image, you have to enter -5% and click on OK again. Saturation controls how close to grey colours are. By decreasing the saturation, you can gradually move an image towards being grey. Increasing the saturation makes the colours deeper and less like pastel shades. Hue is related to the actual colour. Changing the hue, moves colours around the colour wheel in circles. It is almost like the colour swopping described above, instead of rotating RGB in a single large discrete step (green becomes red etc.), changing the hue allows this process to be done in small steps. These operations are useful for correcting scans which have been done at the wrong values of brightness or are discoloured.   Non-linear This allows the most sensitive control of the brightness of an image. The graph on the right of the window shows the output brightness for each value of the input brightness. The resulting change can be applied to the entire image or a selected area of it. The buttons on the far right allow the mapping to be applied to the red, green or blue components individually. The buttons on the left set the form of mapping. Step In this the input is mapped to a discrete set of output values. Commonly called 'posterisation'. The levels of the bands in the graph can be dragged with the mouse select button. Smooth A line is drawn through a number of values. You can drag the points forming the line around. Gamma A common form of correction is to relate the input level (i) to the output (o) by o=iG for G greater than 1 this will make the image darker, for G less than 1 brighter. Threshold In this the output is either 0 or 100%, and you can vary the point (threshold) at which the transition takes place. Levels This allows you to set the number of levels that there will be for the Smooth, Step and Threshold options. Invert When clicked on this will invert the mapping. Linear This makes the levels linear. It may be useful for getting back to sensible values after a session of editing them. Palette Selecting this from the Colour menu will open the palette window. This can be useful just to see what the palette of the current image is. Using the palette you can choose the background colour to be used when an image is extended by the Edit tools (shear, rotate, extend), construct custom palettes, and finally set the foreground colour and tint to be used by the selections on the rest of the Colour menu - Tint, Filter, Add, Subtract and Reverse filter. The top of the area, shows a small rectangle for each entry in the palette. The example on the left has 256 as it would for an 8bpp image. For images with less bpp, there will be less entries. For images with no palette this area will be blank. The four squares at the bottom show the current foreground, background, mask and palette colours. Mask, is the strength of the mask which is applied to new pixels created, for example when an image is rotated. The idea is similar to that of the background colour. The mask value is taken from the colour strength slider. A value of 100% (white) means that all the brightness comes from the image (solid), a value of 0% (black) means that the all brightness comes from whatever the image is rendered on (transparent). Left clicking with on these icons transfers the colour to the colour selector values (see later). Right clicking transfers the colour selector values to the colour. If you left click on the palette area that colour will become the one shown on the palette icon and the colour selector. Right clicking in the palette area will transfer the current colour selector colour to the palette. A similar effect can be achieved by right clicking on the Palette icon. As well as choosing a colour, you can also choose a strength to go with it - a tint. This controls how much effect the colour will have when mixed with other colours. The right bottom part of the palette window allows this strength or tint to be set. The icon under Colour strength, shows the tinted and the original colour. The right hand part of the window, displays the 'current colour'. It can be shown in one of three models, RGB (red green blue, as used by video screen displays), HSV (hue, saturation, brightness which has some intuitive value) and CMYK (cyan, magenta, yellow, black, which is the same model as used in colour printing). The colour wheel displays a plane in HSV space - think of it as a slice through a cylinder. The colour model can be changed by clicking on the RGB, HSV or CMYK buttons. Sliders will appear for the quantities that can be altered. In the RGB and CMYK models there is an additional slider to control the slice through the colour cylinder that is displayed. You can select colours by typing in values (percentages of red, green blue etc.), by clicking or dragging on the colour wheel, or by stepping through values with the arrow icons. The process for using the colour selector is as follows. Left click on a colour icon i.e. the Fore, Back, Mask or Palette icons or the palette area icon. Modify the colour using the colour selector. Set a tint for the colour. Finally store the colour by right clicking on one of the colour icons. It is possible to get a colour from the current image, using the pointer tool, by holding down the SHIFT key and left clicking over the pixel of interest. Right clicking over the palette area on the left will open a menu which allows you to export the palette as a RISC OS palette file or import a palette file. You can also import a palette file by dropping it into the main image window. We now come to the final selections on the colour menu.  Tint Tint takes each pixel in the image, and mixes its colour with that of the current foreground colour. The effect is like mixing light. If the current colour is Yellow then all pixels will become more yellow. How great this effect is, is set by the tint of the current foreground colour. Do not confuse this Tint option with the tint property of colours.  Filter This works like viewing the original image through a colour filter (like looking at a picture through a coloured piece of paper). Colour filters have interesting properties. For example if you look at a pure green object through a pure red filter it will appear black - because no green light can get through a red filter. Only pure red objects will be seen at full strength through a red filter. As usual how much effect the filter has is set by the tint of the foreground colour.  Add The foreground colour is added at equal strength to all the pixels in the image. Again the tint of the colour controls the effect.  Subtract The opposite of Add, the colour is subtracted. Reverse Filter This reverses the effects of putting an image through a colour filter. Imagine you had taken a photograph through a coloured filter, then this option would undo the effects of the filtering, producing an image that looked as if no filter had been used. One use for this is processing scans of colour negatives. This is what you should do with a colour negative scan. 1. Open the colour palette and left click on the film background in the image window, using the Select tool and with SHIFT pressed. Set the colour tint/strength to 100%. Finally right click on the foreground colour icon. You have now set the foreground colour to the same colour as the negative film. 2. Use Reverse filter from the colour menu. 3. Use Invert from the filter menu. Your colour negative is now developed. Scanning at high brightness will help get better results, as will applying some gamma correction. 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Clicking on these icons, will open a sub configuration window for the file type. The options provided for the file types are discussed in the next chapter. The arrows at either end of the strip allow the available file types to be scrolled through. Across the bottom of the configuration window is another row of icons. These allow various aspects of the program to be controlled. Each icon representing a group of related parameters. Again configuration windows can be opened by clicking on the icons. Finally there is a 'Save' button clicking on this will save the configuration of the program so that it is the same when the program is next used.  Memory This controls the programs use of memory. The top slider lets you set the maximum amount of RAM that it will use. The next two bars cannot be adjusted, they show the amount of RAM in use, and the amount of disc space being used as "virtual memory". Note that these bars can be confusing. The RAM bars show the proportion of the total RAM in the computer. The disc bar shows the proportion of free disc space in use. The free space on the disc may be much larger or possibly smaller than RAM. You should not make relative comparisons of the RAM and Disc bars. The writable icon 'Temp file' allows the directory where the temporary file holding image data which will not fit in RAM is held. Clicking on the right pointing arrow to the side of this, will pop up a standard save box. The icon may be dragged to where you want the temporary file to be held. Note that if a temporary file already exists, you cannot change the location immediately this way. It may be useful to leave the memory box open to give you some idea as to how much memory you are using. The RAM and Disc bars will be continuously updated. The default temporary file path is; <%TEMP%> This means use the value of the Windows system variable TEMP. Other Windows system variables can be used when bracketed by %s. It is also possible to insert the name of a Windows registry variable between < >s. The temporary file should be kept on a large area of fast writable disc. Since Windows has a virtual memory system built in, the recommended setting for Max RAM is a large value so that DPScan does not use its own virtual memory. Usually the temporary file will only become active when large images are being handled, in such cases you must have plenty of free space on the disc. Given the well known fact that all hard discs are 25% too small, the situation of the hard disc with less free space than there is RAM is quite common. At any rate using virtual memory requires large areas of empty disc space.  Windows The four buttons on this window control the default appearance of each new window. Whether the window will have rulers, a toolbox, an info palette or if dithering will be enabled for it.  Page This allows the default page size, units and X and Y resolutions to be chosen, by clicking on the appropriate right pointing arrow and making a selection from the resulting menu. These values apply when a new, empty, window is opened.  General There are several sections. The first section allows the Aliasing filter used for the operations on the Edit menu to be set. The second section consists of three writable icons which set the weights used when greyscaling images.  NrYqT NCY@eD N;Y@FSH N}Y@ NcށY@D>< N Y@Q@ NaY@$ N‚Y@JG4 N#Y@ {@ NEY@S8( NcY@\ NCY@+bT N)Y@ NY6U  , NY@8 N(Y@8 N3jY@60 NӫY@jT N Y@< NSNY@@ NY@t< NцY@+  Ns2Y@ўP NtY@nL NY@4D NSY@0 N8Y@x NәY@H8 NsۈY@  NY@$ N}Y@+ NމY@9$ N?Y@ NSY@ NŠY@tVH NY@,$ NSrY@q0 NY@$ NY@  NsVY@t< NY@~ NY@kH N:Y@#D4 N3|Y@] NۂY6U4 0 NC9Y@*,< NzY@8 NY@y NFY6U  $ NyY@X N3Y@tD NY@"  N\Y6U 0 N㹅Y@ NY@D Nc\Y@#D NCY@n< NY@5ud N_Y@  N(ttL %LL P P b P  x  0X]7n@n@)) tL & @8L `m> `m> rx `m>  x  0X]7n@n@))bJT7 L A4'  $ $x6>6>6>610. File Formats In an ideal world there would be just one type of file used for storing bitmap images. In reality there are many thousands, some represent needless duplication, others have been designed to take advantage of different hardware, or to meet different requirements. In any case there is a need to be able to save and load files in different formats so that images can be exchanged with other programs and computers. Different file formats are also of use in different situations. It would be a mistake to assume that you should always use one file type, when often using a different file type can save you a lot of effort. Given the potentially large size of bitmaps, many file formats provide some sort of data compression. By locating redundancies in the data and coding them more efficiently the size of the image files can be reduced. There are two types of compression in use. The first type is "lossless" in this the uncompressed image will be identical to the original image. This sort of compression is similar to that used in compressed filing systems and archive programs. The other type of compression is so called "lossy" compression. In this the decompressed image may be different to the original - the idea being that such changes will be small and not noticeable. Currently only one lossy type is supported - JPEG. Many image file types were originally based on just saving the contents of the screen display. Such formats often do not save resolution data. The display prescription is to just display one dot of the image on one dot of the display. Commonly this will lead to high resolution images appearing too large. If this is a problem you should use file types like TIFF that do not have such shortcomings. It is also possible to change the display resolution - see the description of the info palette for the pointer tool in chapter 4. We now go through the supported file types. For each one, the configuration options will be discussed. See the previous chapter for how to access these options. All the file types have an associate icon. This lets you tell Windows to associate a given file extension with DPScan. Association makes DPScan load files when they are double clicked, it also makes Windows display an icon from inside DPScan for files with the relevant extension. Turning off association will not return the association to the previous setting. To do that you will have to use the facilities in Windows (Windows explorer View->Options) or in the program you wish the file extension to be associated with. As well as the normal extensions like .tif for TIFF files, hexadecimal extensions are supported (ff0 for TIFF files), these are what you may end up with when you transfer a file from RISC OS or may let you resolve any clash of extension names with other programs. Many of the file types e.g. PCX, BMP, GIF, MTV, PBM, Clear, configuration windows allow a default resolution to be set. This is the resolution in dpi which will be given to images of these types when loaded. Setting it to your screen resolution (usually 96 or 120dpi) is a good idea.  Sprite This is the standard RISC OS bitmap file type, as used by Acorn Paint and many other programs. Traditionally sprites come with a "mode" number which defines how they are to be displayed, bpp and resolution etc. The configuration options allow mode numbers to be defined for both rectangular (90x45 dpi) and square (90x90 dpi) pixels. Up until 1994, sprites only held 1, 2, 4, or 8 bpp data. However after that time, a new variation on the sprite format appeared. This can hold 16 or 32 bpp data. For the 16 bpp data 5 bits are given to each of red green and blue, for the 32bpp data 8 bits. If you save a 24bpp image as a sprite it will be saved with 32bpp. Be careful 16 and 32bpp images cannot be used on older (pre 1994 RISC OS) software or hardware. Sprite files can contain more than one image. Images may have a mask. Whilst the 1,2 and 4 bpp formats are straightforward. The 8bpp format has been obfuscated by hardware dependencies. Original 8bpp sprites had 64 palette entries of which only 16 were used - the full 256 colours being synthesised from the palette and the colour numbers. Later 8bpp images have a full set of 256 palette entries. When saving sprites the program will supply a 256 entry palette. This may upset some old software. Deep sprites when selected allows 16 and 32 bpp images to be saved. If not selected these images will be converted to 8bpp. The conversion will be done with the current Change Format settings. New format when selected makes images with 8bpp or less be saved in the new mode number less format. This format also only uses one bit per pixel for masks. Older sprites with a mode number use the same bpp for both the mask and the image. The old format does not support 16 or 32bpp, such images are thus always saved in the new format, regardless of this setting. In effect no resolution data is saved with sprites. CMYK images are supported. Images may contain a mask and this is supported. Sprite files may contain many images. There is a text file called modes.txt stored in the folder in which DPScan is installed. It is a common problem to find that sprites which you want to load have been created in some non-standard (soft) screen mode. The Modes file allows you to enter definitions for these mode numbers. Extensions: spr, ff9.Draw Draw files are the standard RISC OS vector file format. They can contain RISCOS sprites. DPScan displays just the sprites in Draw files, letting you step through them. Saving images as a Draw files is useful because Draw files effectively retain resolution data, unlike sprite files. So Draw is a format you can use on RISC OS which will preserve image sizes. Extensions: drw, aff.  GIF This is the Graphics Interchange Format. Originally invented by Compuserve (an online system or large bulletin board). The motivation was to allow pictures to be downloaded (transferred from one computer to another). It seems one of the design requirements was to allow images to be seen as they arrived. GIF (pronounced 'jiff') made use of the then new LZW data compression technique. GIF files give good results and are deservedly popular. GIF files can contain 1, 2, 3, 4, 5, 6, 7 and 8bpp images. They are therefore only of use for paletted images. GIF files can contain more than one image. In GIF files transparent pixels are represented by one of the colours in the image palette. So for example if you have a 256 colour image with a mask, one of the colours must not be used by the image so that it can be used for transparent pixels. If all 256 colours are in use by the image, then the mask data will be ignored when saving the GIF file. One configuration option is provided. Interlace controls if the image lines are stored contiguously (one after another) or with an interlace (every eighth line etc.). In GIF files transparent pixels are represented by one of the colours in the image palette. So for example if you have a 256 colour image with a mask, one of the colours must not be used by the image so that it can be used for transparent pixels. If all 256 colours are in use by the image, then the mask data will be ignored when saving the GIF file. No resolution data is saved. Extensions: gif, 695.  PCX This is a file format popularised by ZSofts PC Paintbrush package on the PC. Files may contain 1, 2, 4 or 8 bpp. Simple run length data compression is implemented. No resolution data is saved. Extensions: pcx, 697.  BMP This is the Windows and OS/2 equivalent of Acorns Sprite file. Images may contain 1, 4, 8, 16, 24 or 32 bpp data. Simple data compression is implemented. The configuration option allows either Windows 3 or OS/2 headers to be written to saved files. Resolution data is saved. Colour profile information can be saved. The vast majority of .bmp files in existence have a Windows 3 header. A Windows 5 header is required for an embedded profile. What this means, is that if you save an image in .bmp format with an embedded profile some Windows programs may not be able to use the resulting file. Extensions: bmp, 69C.  Clear Given the confusion surrounding Acorn sprite files, and their original inability to support 24bpp, John Kortinck (of Translator fame) invented a file type that was simple and straightforward - hence the name 'Clear'. Clear files can contain 1,2,4, 8 or 24 bpp. There is no data compression. Quite a few RISC OS programs can handle Clear files. No resolution data is saved. Extensions: clr, 690.  MTV This file format was invented to save the output of the MTV ray tracer. It is a simple 24bpp format with no data compression. No resolution data is saved. Extensions: mtv, 699.  PBM In the world of UNIX there are several large suites of general purpose image manipulation software. One such is Jeff Poskanzer 'PBM' toolkit. There are variations on the format to handle grey scale (PGM Portable Grey Map), 1bpp (PBM Portable bitmap) and colour images (PPM Portable Pixel Map). The configuration option Rawbits controls if PBM files will be stored as binary or text files. Binary (Rawbits selected) are much more compact than the text file option. No resolution data is saved. Extensions: pbm, 69e.  JPEG This file format is from the Joint Photographic Experts Group who set out to produce a standard for lossy compression. Technically speaking the file format is JFIF (JPEG File Interchange Format). These files can cope with 24 bit images or 8 bit grey scale data. Because the compression is lossy you should only use JPEG files for saving the final result of image manipulation. However JPEG compression is often excellent, reducing huge files to manageable proportions. The configuration option Quality (0 to 100%) controls how good a representation of the original the file will be. 100% gives no loss of data. Resolution data is saved. Colour profile information can be saved. Extensions: jpg, jpeg, jpe, c85. TIFF This file format goes back to the early days of micro computers. It was an attempt to invent a file type for images that could be used by all programs. Developers of TIFF included Aldus, Lotus and Microsoft. TIFF stands for Tagged Image File Format. As the name hints TIFF files are extendible, more tags can be added to give more information about images. TIFF attempts to be everything to everyone. Unfortunately as a result it is possible to have two programs which both use TIFF files and are completely incompatible. However in many ways TIFF is the file format of choice. TIFF files can contain all bpp images, including paletted and non paletted images. Resolution data is saved with the images, and a file can contain more than one image. Configuration options allow you to choose the data compression method used. For black and white images, special coding techniques from the world of Fax are provided. For colour images there are other techniques. Note that all the black and white options can be toggled off (left click on a selected one) and the colour data compression will then be used for all images. Colour profile information can be saved. Extensions: tif, tiff, ff0. ICO This is a Windows icon. It is a small bitmap intended for icons in the Windows desktop. Files may contain more than one image, the standard sizes which you should stick to if you want your files to be useable everywhere are 16 by 16, 32 by 32 and 64 by 64 pixels. The idea is that all the images are of the same thing, and the one of the most appropriate size is used. Ico files have a maximum width and height of 255 pixels. An error is raised if an attempt to exceed this is made. Images support a form of masking, consisting of two sub images one of which is logically exclusive orrd and one which is logically andd. The thing you need to know is that for masked images to be saved successfully they must have black in their palette (if they have one). The sub images are related to Windows bitmaps (discussed above) so the same colour depths are supported 1, 4, 8, 16, 24 or 32. There is no resolution data. Extensions: ico, 132. CUR This is a Windows cursor. It is actually an ICO file with a different extension, so all the comments above apply. Extensions: cur, 133. PNG Portable Network Graphics. Patent problems with GIF files led to an attempt to define a new open file format that could be used in the same way as GIF files, but which used a compression method free of patents. In fact the compression technique used is Deflation the same as in most Zip files. It can sometimes offer much better compression than e.g. LZW TIFFs on 24bpp images. Compression is lossless. The file format supports resolution data. Extensions: png, b60. EPS Encapsulated Post Script. Consists of converting the bitmap into PostScript and adding a small amount of extra information. DPScan can only save this format, it cannot open EPS files. The EPS configuration window provides options for a preview image and for saving the main image data as an embedded JPEG. The preview section allows the main scale and change format windows to be used to generate the preview image. Good settings are probably a preview of size 20% at 8bpp with an optimised palette. The preview image can either be a TIFF file, glued on to the start of the EPS file - this is PC/DOS style, or in a truly platform independent form (EPSI) coded as hex in comments in the EPS file. Remember that the current TIFF and JPEG configurations will be used for the EPS file - you may want to use TIFFs with no compression. EPS saving supports CMYK, but only when the main image in the EPS is not JPEGd. 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