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You can use -o
to specify the thumbnail image format too. For example:
$ vipsthumbnail fred.jpg ../jim.tif -o tn_%s.png
Will write thumbnails in PNG format.
You can give options to the image write operation as a list of comma-separated arguments in square brackets. For example:
$ vipsthumbnail fred.jpg ../jim.tif -o tn_%s.jpg[Q=90,optimize_coding]
will write jpeg images with quality 90, and will turn on the libjpeg coding optimizer.
Check the image write operations to see all the possible options. For example:
$ vips jpegsave save image to jpeg file usage: jpegsave in filename where: in - Image to save, input VipsImage filename - Filename to save to, input gchararray optional arguments: Q - Q factor, input gint default: 75 min: 1, max: 100 profile - ICC profile to embed, input gchararray optimize-coding - Compute optimal Huffman coding tables, input gboolean default: false interlace - Generate an interlaced (progressive) jpeg, input gboolean default: false no-subsample - Disable chroma subsample, input gboolean default: false trellis-quant - Apply trellis quantisation to each 8x8 block, input gboolean default: false overshoot-deringing - Apply overshooting to samples with extreme values, input gboolean default: false optimize-scans - Split the spectrum of DCT coefficients into separate scans, input gboolean default: false quant-table - Use predefined quantization table with given index, input gint default: 0 min: 0, max: 8 strip - Strip all metadata from image, input gboolean default: false background - Background value, input VipsArrayDouble
The strip
option is especially useful. Many image have very large IPCT, ICC or XMP metadata items embedded in them, and removing these can give a large saving.
For example:
$ vipsthumbnail 42-32157534.jpg $ ls -l tn_42-32157534.jpg -rw-r–r– 1 john john 6682 Nov 12 21:27 tn_42-32157534.jpg
strip
almost halves the size of the thumbnail:
$ vipsthumbnail 42-32157534.jpg -o x.jpg[optimize_coding,strip] $ ls -l x.jpg -rw-r–r– 1 john john 3600 Nov 12 21:27 x.jpg