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Text File | 1991-04-22 | 8.2 KB | 212 lines

>SWIs ---------------------- - The GreyEdit SWI's - ---------------------- The GreyEdit module contains several SWI's, which are used by the main program, !RunImage. Because they may be useful in other programs, all the SWI's contained in this module are discussed in detail below. They are divided into two groups. The image processing SWI's may be useful to any kind of user. The digitiser SWI's may be useful to users that wish to make their own digitizing applications using the Zeridajh Video Digitiser. - The image processing SWI's These SWI's all process or perform computations on an entire image. Images consist of byte-values, i.e. 0(black)-255(white), that represent the pixels' greyvalues. All image-processing SWI's expect a pointer to an image info block in r0. This block contains information about the image to be acted upon : Offset Name Meaning ------ ---- ------------------------------- 0 start pointer to start of image data 4 xpix horizontal resolution in pixels 8 ypix vertical resolution in pixels 12 xskip pixels to skip at end of rows The xskip value enables the image to be actually stored as a sprite. For example, if start=&20000, xpix=637, ypix=512, and xskip=3, then the image has the following structure : &20000 : <637 bytes of image data> <3 bytes alignment, ignored>, i.e. row 1 &20280 : "" "" , i.e. row 2 &20500 : "" "" , i.e. row 3 ..... &6FD80 : "" "" , i.e. row 512 Thus, dis-alignment within the sprite presents no problems, as long as start points to the first valid pixel, and xskip is set to the total row-wastage. SWI GreyEdit_Map ---------------- Maps the image's pixel values. On entry - r0 points to image info block (start/xpix/ypix/xskip) - r1 points to 256-entry pixel value map I.e. for all pixels, new_pixel_value = r1?old_pixel_value SWI GreyEdit_Cut ---------------- Cuts down an image. On entry - r0 points to image info block (start/xpix/ypix/xskip) - r1 points to cut info block (start/left/top/right/bottom/xskip) The word-values in the cut info block determine the new (smaller) size and structure of the image. The new image is a sub-image of the old image, and is defined by the coordinates of its top left corner and its bottom right corner within the old image. It is stored at the address contained in the start value of the cut info block. The xskip given in the cut info block is the xskip value of the new image. The skipped pixels in the new image are all set to 0. The left value may range from 0 to xpix-1, the right value from left to xpix-1, the top value from 0 to ypix-1, and the bottom value from top to ypix-1. The cut info is not checked in any way, so it is your responsibility to supply sensible values. The x/y size of the new image will obviously be right-left-1/bottom-top-1. SWI GreyEdit_Filter ------------------- Applies a filter algorithm to an image. For details on the algorithms refer to 'Technical details' in Docs.Guide. On entry - r0 points to image info block (start/xpix/ypix/xskip) - r1 indicates the filter to be applied 1 - Noise (weak) 2 - Noise (strong) 3 - Gauss 4 - Average 5 - Laplace 6 - X-gradient Sobel 7 - Y-gradient Sobel 8 - Maximum 9 - Minimum SWI GreyEdit_Frequency ---------------------- Calculates the frequencies of greyvalues in an image. On entry - r0 points to image info block (start/xpix/ypix/xskip) On exit - r0 points to frequency table (4-byte counters) I.e. the number of occurences of greyvalue g is r0!(g<<2). SWI GreyEdit_Equalize --------------------- Applies the histogram equalization algorithm to an image. On entry - r0 points to image info block (start/xpix/ypix/xskip) On exit - r0 points to cumulative histogram table (4-byte counters) - r1 points to equalization greyvalue map To equalize the image, this SWI should be followed by GreyEdit_Map, using the map returned at r1. The g'th entry in the cumulative histogram table represents the added frequencies of the greyvales from 0-g, i.e. the 255th entry is always equal to the total number of pixels in the image, xpix*ypix. - The digitiser SWI's These SWI's all drive the Zeridajh Video Digitiser podule. When it is not present (see GreyEdit_CheckDigi), they should not be called. SWI GreyEdit_CheckDigi ---------------------- Checks presence of the Zeridajh Video Digitiser podule, and initialises usage of the other digitiser SWI's if it is. Thus, it should always be the first SWI called. On entry - r0 contains podule's ID code On exit - r0 contains podule's base address if it is present, else 0 SWI GreyEdit_Grab ----------------- Digitises a video image. On entry - r0 points to image data buffer - r1 contains size of image data buffer - r2 contains required horizontal resolution in pixels - r3 contains required vertical resolution in pixels - r4<>0 gives 'line skip' (scanlines skipped at top of video image), else default of 20 is taken (approx. center of video image) - r5<>0 gives lowest delay factor, else default of 200 is taken. DO NOT CHANGE, I.E. USE 0. - r6 contains flags bit 0 - when set (1) prevents video DMA disable when grabbing bit 1 - when set (1) prevents re-enable of video DMA on ok exit On exit - r0 points to error block (V set) if error occured This SWI digitizes a video image, storing it in the supplied image data buffer. The range of available resolutions is restricted to 5*xfac/1*yfac for x/y respectively, where xfac/yfac is a power of 2, up to 640x512. When r2/r3 lies outside this range, the value is rounded up to the nearest available value. I.e. 160x128 is a valid resolution, but 161x128 would be rounded up to 320x128. When the image buffer is too small to contain the image, an error is returned. The value of r4 determines the number of scanlines that are skipped at the top of the video image. When a value of 0 is given, the default of 20 is taken, which skips approximately the same number of lines at the top and bottom of the video image (i.e. the 'center' is taken). The value of r5 should always be 0. The delay factor plays an important role in the digitizing process, so it should not be tampered with. It is only present for (future) development purposes. Video DMA is usually disabled when grabbing, and re-enabled on exit. Both of these 'effects' can be switched off by setting the appropiate bits in r6. Setting bit 0 may cause the image to be distorted, when the processing delays introduced by video DMA prevents the software to keep its synchronization with the video image. SWI GreyEdit_VideoDMA --------------------- Turns video DMA on/off. On entry - r0 contains 0 to turn video DMA off, or 1 to turn it on. SWI GreyEdit_VideoTiming ------------------------ Returns a number of values representing the vsync and hsync signals present in the video image. Also returns a rough classification of the video signal based on the vsync and hsync signals. The values are returned in a signal buffer. They are bit values (0/1), which represent the exclusive OR of (NOT Burst,Vsync) from the LM1881 on the podule. The bit-values are packed 8 at a time in bytes (bit 0 first). The entire buffer is filled. Video DMA is disabled temporarily. On entry - r0 points to signal buffer - r1 contains length of signal buffer in bytes On exit - r2 gives a video signal type code -1 = no video signal detected 0 = normal video signal 1 = MacroVision protected video tape signal SWI GreyEdit_Sensitivity ------------------------ Sets the podule's video signal sensitivity. This only works if the PCF8591 chip is present on the podule. On entry - r0 contains sensitivity value and flags bit 0-7 : sensitivity value bit 8 : if set (1) value is percentage (0(low)-100(high)) if clear (0) value is 0(high)-255(low) On exit - r0 contains -1 if the PCF8591 is not present, else 0 Where 'low' is lowest sensitivity ('dark' images), and 'high' highest sensitivity ('light' images).