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Thread: JPG Specific Quality Target Batch

  1. #1

    Default JPG Specific Quality Target Batch

    I'd like to know if it is possible to target a specific jpg quality when doing batch conversion. I have lots of jpg with different quality, some are 60, 70, 90, 95, and 100 and I want the maximum to be 90, so I need a way to batch convert all the files to quality 90 BUT SKIPPING files that are lower than 90, because it would increase the file's size and I don't want that.

    I'd love irfanview (or even Windows Explorer) to have an option to sort files by jpg quality, that way I could just select those I want to convert.

    Thanks in advance!

  2. #2
    Moderator Enterprise User Bhikkhu Pesala's Avatar
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    No, there is no way to do that. The compression quality is estimated on loading the file. If the files are the same dimensions, there is a good chance that the largest files will have the highest quality/compression value of 90 or more, but you would have to check each one using the Information button, then move those files to a new folder or add them to a batch job.

  3. #3

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    I see, that's unfortunate though, hopefully one day that feature could be added to a new release. Thanks!

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    Power User j7n's Avatar
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    If you have only a few specific quality presets that need conversion, such as 95 and 100, you could search for the hexadecimal strings of the quantization tables in a file manager, such as Total Commander. Unfortunately, it is not possible to search for a range of qualities, as the sequence 0101010101 representing highest quality also occurs in another place. The string to use is 4300.. followed by a sequence of small values.

    (There are more than 10 possible qualities above 90, some programs with their own codec, such as Photoshop, have different quantization profiles. But high quality always starts with 1s or 2s. The estimation works by pulling some kind of average sum of these.)
    Last edited by j7n; 12.08.2019 at 05:15 PM.

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