Take the 2-minute tour ×
Ask Ubuntu is a question and answer site for Ubuntu users and developers. It's 100% free, no registration required.

I'd like to compress my screenshots as much as possible before I send them via email. The best compression ratio I only got with some work on each screenshot:

  • first I took the screenshot with shutter: 1920x1080px, PNG compression 9 -> around 450Kb
  • then I uploaded it to http://tinypng.org/ -> got the same picture with quantisation but only around 150Kb left

how could I achieve such a good compression within a screenshot tool like shutter? But shutter has no "quantisation" option.

The Quality is not that important, I wouldn't mind to have it more lossy. Maybe with GIF it would be possible to compress smaller? Or with less colors?

The technique of http://tinypng.org seems fabulous:

similar colours in your image are combined. This technique is called “quantisation”. Because the number of colours is reduced, 24-bit PNG files can be converted to much smaller 8-bit indexed colour images. All unnecessary metadata is stripped too. The result: tiny 8-bit PNG files

share|improve this question
    
There is a tool in the repos for this. I can't remember the name off hand but if/when I find it, I'll post it here. –  RolandiXor May 21 '13 at 23:38

2 Answers 2

optipng is certainly worth a look at . It's command-line but you could write a .desktop handler for it. It's fairly simple to use for batching:

optipng -o7 *.png

But note it's destructive. It will overwrite your files. This is usually fine but if you're using a fat format (Adobe Fireworks PNG for example), you might lose useful. Here is the full list of options:

$ optipng -h
OptiPNG 0.6.4: Advanced PNG optimizer.
Copyright (C) 2001-2010 Cosmin Truta.

Synopsis:
    optipng [options] files ...
Files:
    Image files of type: PNG, BMP, GIF, PNM or TIFF
Basic options:
    -?, -h, -help   show this help
    -o <level>      optimization level (0-7)        default 2
    -v          verbose mode / show copyright and version info
General options:
    -fix        enable error recovery
    -force      enforce writing of a new output file
    -keep       keep a backup of the modified files
    -preserve       preserve file attributes if possible
    -quiet      quiet mode
    -simulate       simulation mode
    -snip       cut one image out of multi-image or animation files
    -out <file>     write output file to <file>
    -dir <directory>    write output file(s) to <directory>
    -log <file>     log messages to <file>
    --          stop option switch parsing
Optimization options:
    -f  <filters>   PNG delta filters (0-5)         default 0,5
    -i  <type>      PNG interlace type (0-1)        default <input>
    -zc <levels>    zlib compression levels (1-9)       default 9
    -zm <levels>    zlib memory levels (1-9)        default 8
    -zs <strategies>    zlib compression strategies (0-3)   default 0-3
    -zw <window size>   zlib window size (32k,16k,8k,4k,2k,1k,512,256)
    -full       produce a full report on IDAT (might reduce speed)
    -nb         no bit depth reduction
    -nc         no color type reduction
    -np         no palette reduction
    -nx         no reductions
    -nz         no IDAT recoding
Optimization details:
    The optimization level presets
        -o0  <=>  -o1 -nx -nz
        -o1  <=>  [use the libpng heuristics]   (1 trial)
        -o2  <=>  -zc9 -zm8 -zs0-3 -f0,5    (8 trials)
        -o3  <=>  -zc9 -zm8-9 -zs0-3 -f0,5  (16 trials)
        -o4  <=>  -zc9 -zm8 -zs0-3 -f0-5    (24 trials)
        -o5  <=>  -zc9 -zm8-9 -zs0-3 -f0-5  (48 trials)
        -o6  <=>  -zc1-9 -zm8 -zs0-3 -f0-5  (120 trials)
        -o7  <=>  -zc1-9 -zm8-9 -zs0-3 -f0-5    (240 trials)
    The libpng heuristics
        -o1  <=>  -zc9 -zm8 -zs0 -f0        (if PLTE is present)
        -o1  <=>  -zc9 -zm8 -zs1 -f5        (if PLTE is not present)
    The most exhaustive search (not generally recommended)
      [no preset] -zc1-9 -zm1-9 -zs0-3 -f0-5    (1080 trials)
Examples:
    optipng file.png                (default speed)
    optipng -o5 file.png            (moderately slow)
    optipng -o7 file.png            (very slow)
    optipng -i1 -o7 -v -full -sim experiment.png

There are other tools (pngcrush for example) and you might find they're more useful but I've never strayed from optipng, just for its no-nonsense simlpicity.

There's a fairly comprehensive PNG compression shoot-out here that's quite fun:

share|improve this answer
    
optipng works great, how could I include it into the screenshoter of the system? –  rubo77 Aug 7 '13 at 11:41

You can add this plugin to shutter:

Screenshot tool with integrated optipng or pngcrush

that gives you the option to compress the created screenshot with optipng

share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.