JPEG red-shifted on download tasks

Our client loaded an JPEG to MediaBin and on download the image is minimally red-shifted.

I've ruled out EXIF data by cloning those to the exported image with exiftool.

Also it's not due to the Color Converter step in the export task as I created a test one that does not convert colors and the output is the same as with default JPEG export tasks.

This suggests that the decoder and/or encoder mangle up colors.

Is there a way to fix this? Can I debug it further?

Here's a sample comparison: http://grab.by/H2UK the original is on the right.

One thing I've noticed with exiftool:

Original:

Y Cb Cr Sub Sampling : YCbCr4:4:4 (1 1)

Export:
Y Cb Cr Sub Sampling : YCbCr4:4:0 (1 2)

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Comments

Zamber

Traced this back to encoding quality. There are also (less apparent) loses even when decoding and encoding a 100% quality JPEG.

tposton

Due to the lossy format of JPEG, encoding a JPEG again into a JPEG will always produce artifacts in the output. Use the (Get Original) task, or encode to a non-lossy format.