![]() ![]() For example, perhaps you somehow know that a JPG is in Adobe98 space, even though it has no embedded profile. You can also specify a fallback input profile to use if the image has no embedded one. Tn_shark.jpg will look identical to a user, but it’s almost half the size. The magic string srgb selects a high-quality sRGB profile that’s built into libvips.) (You can use the filename of any RGB profile. $ vipsthumbnail shark.jpg -export-profile srgb -o tn_shark.jpg Now transform to sRGB and don’t attach a profile (you can also use strip, though that will remove all metadata from the image): All web browsers assume that images without an ICC profile are in sRGB colourspace, so if you move your thumbnails to sRGB, you can strip all the embedded profiles. You can use this to move all thumbnails to the same colour space. Vipsthumbnail will optionally put images through LittleCMS for you. Strip almost halves the size of the thumbnail: Many image have very large IPCT, ICC or XMP metadata items embedded in them, and removing these can give a large saving. Strip - Strip all metadata from image, input gbooleanīackground - Background value, input VipsArrayDouble ![]() Quant-table - Use predefined quantization table with given index, input gint Optimize-scans - Split the spectrum of DCT coefficients into separate scans, input gboolean Overshoot-deringing - Apply overshooting to samples with extreme values, input gboolean Trellis-quant - Apply trellis quantisation to each 8x8 block, input gboolean No-subsample - Disable chroma subsample, input gboolean Interlace - Generate an interlaced (progressive) jpeg, input gboolean Optimize-coding - Compute optimal Huffman coding tables, input gboolean Profile - ICC profile to embed, input gchararray For example:įilename - Filename to save to, input gchararray Will write jpeg images with quality 90, and will turn on the libjpeg coding optimizer.Ĭheck the image write operations to see all the possible options. You can give options to the image write operation as a list of comma-separated arguments in square brackets. You can use -o to specify the thumbnail image format too. Now both input files will have thumbnails written to a subdirectory of their current directory. Now both thumbnails will be written to /mythumbs, even though the source images are in different directories.Ĭonversely, if -o is set to a relative path, any path component from the input file is prepended. This lets you write all of your thumbnails to a specific directory, if you want. If the pattern given to -o is an absolute path, any path components are dropped from the input filenames. tif in this case) and then substitute the name into the -o option, replacing the %s So this example will write thumbnails to tn_fred.jpg and tn_jim.jpg. $ vipsthumbnail fred.jpg jim.tif -o tn_%s.jpgįor each of the files to be thumbnailed, vipsthumbnail will drop the extension (. This is a pattern which the input filename is pasted into to produce the output filename. You set the thumbnail write parameters with the -o option. ![]() This can make linear light thumbnailing of large images extremely slow.įor example, for a 10,000 x 10,000 pixel JPEG I see: The downside is that in linear mode, none of the very fast shrink-on-load tricks that vipsthumbnail normally uses are possible, since the shrinking is done at encode time, not decode time, and is done in terms of CRT voltage, not photons. Vipsthumbnail has an option to perform image shrinking in linear space, that is, a colourspace where values are proportional to photon numbers. Arithmetic averaging really ought to be in terms of the number of photons, but (for historical reasons) the values stored in image files are usually related to the voltage that should be applied to the electron gun in a CRT display. Shrinking images involves combining many pixels into one. ![]()
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