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There are five possible filter types that can be specified separately on each scan line and several possible strategies for searching LZ77 matches. Thus, there are a very large number of different combinations for how the image can be compressed. Which combination gives the best compression will
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PNG images contain chunks with information about the image, such as its resolution (the phys chunk), the time it was last modified (the tIME chunk), and textual metadata (the text chunk and its variants). With pngcrush, a user can edit or remove those ancillary chunks.
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Since most graphics software embed the extra color-correction data, which is normally not needed, removing it can produce file sizes that are up to 40% smaller than the original. pngcrush, when told, will also losslessly reduce the bit-depth of images or apply a
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pngcrush can be used to change the color encoding of an image. For example, if an image contains 10 colors but has a color palette of 256 entries (8-bit), pngcrush can be used to reduce the color palette to a 4-bit one and truncate the palette to 10 entries.
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pngcrush can also change the color type of the image. For a true-color image, changing the color type from 2 to 0 converts it to greyscale. Greyscale images are generally smaller than truecolor images because, in addition to the optional
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pngcrush compresses the image with multiple different combinations and then stores the smallest of the resulting files. Since it is not possible to go through all the combinations, pngcrush uses heuristics to choose the methods to try.
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by trying various combinations of compression methods and delta filters. It can also be used for various manipulations of PNG images, such as changing the
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crushing, which will try 176 different crushing methods on version 1.8.12 and later or 148 crushing methods on versions 1.7.45 through 1.8.11.
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By default, pngcrush uses just a few common methods to crush the file. The optional "-brute" argument can be used for
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when possible if doing so results in a smaller file size. All ancillary chunks and text chunks can be removed.
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algorithm (which tries to find repeated byte sequences in the source data), and then further compressed with
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The main use of pngcrush is for reducing the size of the image data contained in the IDAT section.
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One of pngcrush's features is the ability to remove all the color-correction data (
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Even Faster Web Sites: Essential
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395:"PNG and MNG tools - Browse /pngcrush/1.8.13 at SourceForge.net"
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The main purpose of pngcrush is to reduce the size of the PNG
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Reducing file size by removing color-correction data
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466:"The Sad Story of PNG Gamma "Correction""
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238:. This combination is referred to as
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513:. Academic Press. pp. 386–388.
337:Free and open-source software portal
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464:Sivonen, Henri (21 April 2003).
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494:. O'Reilly Media. p. 142.
314:Chunk and metadata manipulation
281:color profile) from PNG files.
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544:pngutils for the Win32 console
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590:Free software programmed in C
511:Lossless Compression Handbook
422:"A guide to PNG optimization"
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16:Command-line PNG optimiser
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509:Sayood, Khalid (2003).
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370:"pngcrush changelog"
240:deflate compression
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381:SourceForge
277:, standard
255:brute force
191:open-source
153:Similar to
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565:CloudFlare
356:References
202:losslessly
114:Written in
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64:2017-08-29
561:developed
213:bit depth
172:/pngcrush
323:See also
183:pngcrush
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449:31 July
427:31 July
401:27 July
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161:Website
149:License
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350:Zopfli
345:PNGOUT
267:gamma
185:is a
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557:SSE2
553:zlib
515:ISBN
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451:2010
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232:LZ77
189:and
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93:.net
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279:RGB
198:PNG
170:.io
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