An efficient tool for creating thumbnails of PNG files.
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SYNOPSIS pngscale <input file> <output file> <width px> <height px> <input file> must refer to a valid PNG image. Output will be in PNG format regardless of what name is specified. <width px> and <height px> give the width and height of the output file in pixels. If either <width px> or <height px> is set to -1, the other is automatically set in such a way as to preserve the aspect ratio of the original image as closely as possible. BUILDING AND TESTING To build pngscale, the libpng library is required. On Debian and Ubuntu this can be installed with: sudo apt-get install libpng-dev Afterwards, run "make" to build. The pngscale binary will appear in the current directory. Tests can be run with "test/test". DESCRIPTION pngscale is a specialized tool for scaling of PNG files, intended primarily for creating thumbnail images. It works scanline by scanline, so it's memory-efficient even on extremely large PNG images, taking only about 11 MB of RAM in experiments. It is also faster than ImageMagick convert, particularly on large images, running about twice as fast on a 50 megapixel file. It produces 32-bpp RGBA thumbnails of RGBA images and palettized images with transparency, 24-bpp RGB thumbnails of RGB images and palettized images without transparency, and 8-bpp grayscale thumbnails of grayscale images. Output has 8 bits per channel regardless of bits per channel of the input. It has not been tested with progressive or interlaced images, and upscales images using bilinear interpolation. Error messages are currently English-only. AUTHORS pngscale is produced by Derrick Coetzee and released under the MIT/X11 license, which permits any use commercial or noncommercial as long as the license statement is retained. It is based on a sample by Guillaume Cottenceau and contributors released under the MIT/X11 license at http://zarb.org/~gc/html/libpng.html Latest version of pngscale available from: https://github.com/dcoetzee/pngscale