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I m trying get a scaled down version of a jpeg with jpegtran by using the scaling feature.

this works (it produces a jpeg that can be opened by any program)

cjpeg.exe -scale 8/16 -outfile halfrez.jpg -optimize -progressive fullrez.ppm

but this don't (it produces a jpeg that can't be opened by windows explorer or chrome for example)

jpegtran.exe -scale 8/16 -outfile halfrez.jpg -optimize -progressive fullrez.jpg

I suspect that jpegtran is using the new smartscaling feature that makes the jpeg not compatible, but with block size of 8 it should be ok and it's working with the cjpeg compressor.

any help on how I scale the jpeg with DCT and stile being compatible?

fred_
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  • How is this related to C language? – Gerhardh May 07 '19 at 07:36
  • @Gerhardh both tools have a C API if a c api solution exist I would like to use it – fred_ May 07 '19 at 07:37
  • "Doesn't work" is no error description. In which way does it fail? Does the program throw an error message? Is the resulting file not usable in a certain program? – Gerhardh May 07 '19 at 07:37
  • If you want to use a C API, then please show us your sorce code that you have written so far. Using a 3rd party program is a total different thing. Those would be different questions. – Gerhardh May 07 '19 at 07:38
  • yes I wrote it in the title "it can't be opened" I will modify the text – fred_ May 07 '19 at 07:39

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