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spr_fsi ======= Version 1.20 (10-Jan-1998) SPRtools block 1e release. (C) 1993-4 DEEJ Technology PLC Features -------- Sprite processing tools, features provided; Increase / Decrease bits per pixel (number of colours), Floyd Steinburg Integer dithering, Image scaling with true sub-sampling (anti-aliasing) and interpolation, Image cropping Dynamic intensity range expansion, Gamma correction, Image inversion, Filters including smoothing, sharpening, noise removal & user defined Support for common fixed palettes, Palette optimisation, Restrictions ------------ Enough memory must be available to hold the source image and two lines of the destination image. Further memory is required by certain operations such as filtering. Palette optimisation can require a large amount of memory for images with thousands of colours. Only the first sprite in the file is recognised. Syntax ------ spr_fsi [-bpp <bpp>] [-scale <scale>] [-crop <crop>] [-palette <palette>] [-invert] [-expand] [-gamma <gamma>] [-filter <filter>] [-aspect] [-nodither] [-nointerp] [-quiet] [-help] [-in <input sprite file>] [-out <output sprite file>] [-err <progress/error file>] Options may be abrieviated to the minimum unique form. All options and parameters are case specific. Files default to stdin and stdout with progress or errors to stderr. -bpp <bpp> <bpp> = {1 | 2 | 4 | 8 | 15 | 24 } Bits per pixels in the output image. The default is 24. The 24 bpp option produces the standard 24/32 bit deep sprite format, a (non-standard) true 24 format is also available, which is described later. -scale <scale> <scale> = {<xsize> ,<Ysize> | <XYmul>:<XYdiv> | <Xmul>:<Xdiv>,<Ymul>:<Ydiv> } The amount the scale the output image can be specified in three ways. <Xsize>,<Ysize> scales to an absolute size e.g. -scale 1280,1024 for a sprite 1280x1024 pixels <XYmul>:<XYdiv> scales both axis by the same ratio e.g. -scale 3:2 to expand by 3/2 (1.5) <Xmul>:<Xdiv>,<Ymul>:<Ydiv> scales each axis separately e.g. -scale 3:2,1:2 to expand horizontally by 3/2 and reduce vertically by 1/2 Scales which would produce a very small output sprite, or equate to an expansion of more than 128x in any direction are prevented. The scale defaults to 1:1 in each direction, unless the input image has rectangular pixels and the -aspect flag is not set, in this case a scale of 1:1,2:1 is used to covert the sprite to use square pixels. -crop <crop> <Crop> = <left>,<top>,{<right> | <+Xsize> | <-right>}, {<bottom> | <+Ysize> | <-bottom>} Crops the source image to the desired size. For a source image of 160x128, to crop 5 pixels from each edge the following could be used. e.g. -crop 5,5,-5,-5 or -crop 5,5,145,123 or -crop 5,5,+150,+118 -palette <palette> <palette> = {rgb | grey | desktop | win3 | fix | opt } Selects the palette type for output sprites with 1-8 bpp. The palette defaults to the same as the input sprite. If the input sprite does not have a palette, the default for a RISC OS mode with the same bpp is used. Certain palette types may only be used for some numbers of bits per pixel in the output sprite. The ‘rgb’ palette can be used with bpp 4 and 8. In 4 bpp the palette gives 9 grey levels, 6 fully saturated colours and orange, in a layout designed to be desktop friendly. In 8 bpp the palette gives 46 grey levels plus a 6x6x6 level RGB colour cube (combinations of 6 levels for each component). The ‘grey’ palette gives linear grey scales for bpp 1-8, giving 2 to 256 grey levels. The ‘desktop’ palette gives the standard 16 colour RISC OS desktop palette in 4 bpp, and the standard VIDC1 256 colour mode palette in 8 bpp. The ‘win3’ palette gives a Windows 3 palette in 4 bpp, consisting of 4 grey levels, 6 fully saturated colours and 6 half brightness colours. In 8 bpp a custom (non-Windows) palette with 176 grey levels, a 4x4x4 level colour cube plus 18 RGYBMC shades is used. The ‘fix’ palette will use the input sprites palette (or the default) but will convert old type 12 bit palettes stored in the sprite to full 24 bit. e.g. &B0G0R0xx to &BBGGRRxx The ‘opt’ palette will examine the input sprite after all pre-processing operations have been performed, and will choose the best combination of colours to use in the output image. More details on this process are given below. This option can only be used for output sprites of 4 or 8 bpp. -invert Invert the source image before processing. -expand Expand the dynamic range the source image before processing. Expand works by finding the lowest and highest intensity pixels in the image, the colours of all pixels in the image are then adjusted so that the intensities range from zero to maximum. -gamma <gamma> <gamma> = positive floating point number Gamma correction can be performed on the source image before processing. The default value is 1.0 which has no effect. Values >1.0 (2.2 is the recognised standard) are used to move the contrast detail in the image to the brighter part of the intensity range. This use useful for correcting scanned images and for preparing sprites for printing. Values less than 1.0 can be used to move detail to darker intensities. -filter <filter> <filter> = {filter> | <user filter> } Filters can be used to perform a variety of image processing on the image before further processing. See later for a description of how filtering works. <standard filter> = filter name:- sharpen1 - Sharpen week sharpen2 - Sharpen medium sharpen3 - Sharpen strong smooth1 - Smooth week smooth2 - Smooth medium smooth3 - Smooth strong average - Averages with surrounding pixels noise1 - Noise removal week noise2 - Noise removal medium noise3 - Noise removal strong edge - Horizontal and vertical edge extraction edgeV - Vertical edge extraction edgeH - Horizontal edge extraction edgeNW - Edge extraction along a 45 degree angle edgeNE - Edge extraction along a 45 degree angle edgeSW - Edge extraction along a 45 degree angle edgeSE - Edge extraction along a 45 degree angle emboss1 - 3D embossing effect emboss2 - 3D embossing effect, inverted <user filter> = <a>,<b>,<c>,<d>,<e>,<f>,<g>,<h>,[<mul>,[<div>,[<add>,[<diff>]]]] Where <a> to <h> are the rows and columns of the 3x3 filter matrix. <mul> and <div> are the summation scaling factors which default to 1. <add> is an optional component to be added after scaling. <diff> is the optional noise filtering level. All numbers are positive or negative integers except <div> and <diff> which must be positive. -aspect Normally all sprites containing rectangular pixels are converted to square pixels during processing (doubling the Y resolution), if the -aspect flag is given a rectangular pixel input sprite will give a rectangular pixel output sprite. -nodither This option can be used to prevent Floyd Steinburg Integer dithering from being used during processing. This will speed up processing but will result in a poor quality output. It has no effect when the output sprite is 24 bpp. -nointerp This option prevents pixel area summing or interpolation being used when scaling the image (see the section below on scaling). This will speed up the scaling of images, but with a reduction in quality. It can be used when scaling up an image to prevent the loss of sharpness caused by interpolation. -quiet Prevents the printing of the state of options on stderr during processing. Progress and errors are still output. -help Prints a syntax summary. Info ---- True 24 bit sprite format: spr_fsi normally produces standard RISC OS deep sprite 24/32 bpp format when using -bpp 24, this format is 25% larger than other 24 bit formats and does not compress as well. By using ‘-bpp 8 -palette rgb’ a non standard true 24 bit deep sprite can be produced. It will not be understood by RISC OS applications, but can be used as a storage format for sprites to be used again with spr_fsi. The format has a sprite mode specifier of type 8 (currently unassigned in RISC OS 3.5) and stores pixels as consecutive three byte quantities (blue, green and red bytes) padded to the next word boundary at the end of each line. Scaling spr_fsi uses two techniques to improve the scaling of images. The first is used when scaling down an image, where each output pixel will depend on many pixels in the input. An area of the source image corresponding to a pixel in the destination image is summed to give an average colour. This achieves the effect of anti-aliasing which reduces loss of detail due to scaling down. When scaling up a pixel in the input is converted to many pixels in the output. To prevent a blocky image pixels are interpolated to achieve a smooth graduation between them, rather than sharp boundary. This produces a much smoother image at the expense of some sharpness (the image can be pre-sharpend first using a filter). If the image is being scaled up in one direction and reduced in another the two techniques are used together. Anti-aliasing and interpolation may be turned off using -nointerp. Optimised palette When reducing the number of bits per pixel of an image the various fixed palette types can be chosen to represent colours which will be close to the original. Most fixed palettes aim to cover the colour cube by providing shades which have combinations red, green and blue ranging from zero to maximum. These fixed palettes work well for images which have a large range of colours spanning the colour cube, but where an image has for example, a large number of green shades, a few reds and no blues, many colours in the fixed palette will not be used, and the green shades will be reduced to a far few number in the output. In this case a palette with more green shades and no blue would be more appropriate. When reducing images down to 8 (or 4) bpp the -palette opt option will cause the input sprite to be analysed and the 256 (or 16) colours which will give the best possible match to the original image chosen, and used in the output images palette. After any pre-processing operations have been performed, a histogram of all the colours used in the input image is built. The histogram is then filtered to remove colours which are only used a few times to reduce the amount of calculation. The remaining colours are picked out so as to reduce the difference between the source and destination images as much as possible. This is calculated by the amount of use of the colour and how close similar colours are to it. Usually the optimised palette will generate an image which is much closer to the original, with dithering greatly reduced. For some images however, the results may not be as pleasing as one of the fixed palettes. Experimentation may be necessary. Filters Filters work by taking a pixel and modifying its value depending on the 8 surrounding pixels. The filter consists of a 3 by 3 matrix, the center corresponding to the current pixel. The values in the matrix are used to multiply the value of the pixel under it, values may be positive or negative e.g. 1 2 1 The center pixel is multiplied by 4, its 2 4 2 neighbours horizontally an vertically are 1 2 1 multiplied by 2, and its diagonals by 1. The sum of the nine pixels multiplied by the matrix elements is multiplied and divided by scaling factors to reduce its range back to the valid values for a pixel. In the above example the sum comes to 16x, so it must be divided by 16. Another value may be added to the sum to brighten the pixel (+ve) or darken it (-ve). Finally a differencing filter value can be given. If the difference between the original pixel and the result of the above process is greater than the difference value the pixel is unchanged, other wise it is replaced with the filtered value. If no difference is given the pixel is always replaced. Filters work on each colour component separately and can produce colour changes, e.g. the edge extracting filter. Filters work on the input image and can only use the closest colours in the input image to represent the desired filter values. It is recommended that filter is done with as many bits per pixel as possible. e.g. if an 8 bpp image is going to be filtered to and increased to 24bpp, the increase depth is done first, followed by another run to do the filtering. Processing The main processing done by spr_fsi is the scaling and the change in colour depth which are done at the same time. Other pre-processing options are performed before this in the following order. filter (modifies input image in memory) invert (modifies palette only if image <= 8bpp) expand (modifies palette only if image <= 8bpp) gamma (modifies palette only if image <= 8bpp) optimise palette (only effects output image) Certain operations such as filtering should be done with the maximum bpp, and others may give better results if done after scaling. Two (or more) runs of spr_fsi can be performed to achieve the best results. Deinterlacing To remove interlace artifacts from digitised images (casued by the odd an even fields of a video frame differing when there has been movement, giving jagged edges of objects on alternate lines), the following processing options can be used:- Scale to half vertical height using no interpolation (just remove every other line) spr_fsi -scale 1:1,1:2 -nointerp -in <infile> -out <outfile> Scale back up to full height spr_fsi -scale 1:1,2:1 -in <infile> -out <outfile> Apply slight vertical sharpening (the 5 can be alterned to increase or decrease the effect) spr_fsi -filter 0,-1,0,0,5,0,0,-1,0 -in <infile> -out <outfile> See also spr_info. !ComndCTRL configuration file: spr_fsi