Jpeg-recompress -quality high -min 60 image.jpg compressed.jpg This may lead to unintended behavior for specific use cases (see #12 for an example), so you can use -subsample disable to disable this subsampling. Most digital cameras do the same because of limitations in the human eye. By default, the JPEG encoder subsamples the non-luma channels to two pixels (often referred to as 4:2:0 subsampling). For each 2x2 block of pixels per color channel (four pixels total) it can store four pixels (all of them), two pixels or a single pixel. The JPEG format allows for subsampling of the color channels to save space. Note: The SmallFry algorithm may be patented so use with caution. Linear-weighted BBCQ-like ( original project, 2011 BBCQ paper) Multi-scale structural similarity (slow!) ( 2008 paper) The following metrics are available when using jpeg-recompress. They may differ on individual photos (like above) because each metric considers different parts of the image to be more or less important for compression. Why are they different sizes? The default quality settings are set to average out to similar visual quality over large data sets. By comparison the veryhigh quality setting chooses a JPEG quality of 93 and saves 70% of the file size. The recompression algorithm chooses a JPEG quality of 80. By default SSIM is used, which lowers the file size by 88%. The left shows the original image from the camera, while the others show the output of jpeg-recompress with the medium quality setting and various comparison methods. Demoīelow are two 100% crops of Nikon's D3x Sample Image 2. Some basic photo-related editing options are available, such as removing fisheye lens distortion. The better the quality of the input image is, the better the output will be. In fact, you can use jpeg-recompress as a replacement for cjpeg by using PPM input and the -ppm option. There is no need for the input file to be a JPEG. By default all EXIF/IPTC/XMP and color profile metadata is copied over, but this can be disabled to save more space if desired. This is a lossy operation, but the images are visually identical and it usually saves 30-70% of the size for JPEGs coming from a digital camera, particularly DSLRs. Jpeg-archive -quality medium -method smallfry jpeg-recompressĬompress JPEGs by re-encoding to the smallest JPEG quality while keeping perceived visual quality the same and by making sure huffman tables are optimized. # Compress a folder of images cd path/to/photos
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