JPEG Compression

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Various dialogs in Photo Mechanic offer an option for resizing and compressing files using the JPEG file format. The ‘Quality’ slider has no numbers on it but there are in fact 101 steps which can be chosen - 0 to 100. 100 can be considered an almost lossless compression and will therefore produce the biggest file sizes, although still considerably smaller than TIFFs.

Jpgcompression.jpg

Quality in the 90s compresses more and offers a good compromise between size and quality.

Quality in the 50-80s range are hard to tell apart from the higher quality settings but offer small file sizes.

Quality in the 20-40s range are heavily compressed but are good for small web files.

0 - 10 is not recommended, except for the following:

If you check the box "Limit file size to:" Photo Mechanic will use the quality slider as a lower limit. If you absolutely need to limit a file size to a certain number, then check the box and type in your chosen size. Then set the quality slider to 0. Photo Mechanic will automatically choose a quality (if possible) that will result in the desired file size. In some cases, even at quality 0, extremely low file sizes will not be possible. Photo Mechanic will do its best.


Qualitycomp.jpg


Quality 100 is almost indistinguishable from the uncompressed file and is compressed at around 3:1. Quality 50 is more than adequate and represents a compression ratio almost 5:1. Quality 0 is poor quality but very small at 60:1 compression.

It is important to note that the file size of a compressed image depends on the subject matter and a complex shot with fine detail will not compress as small as a simple image using the same Quality setting.

Subsample Chroma: Check this box to reduce the file size even further. Chroma information is reduced leading to image quality losses in some cases.