I am having to deal with CMYK JPEGs extracted from a PDF source. The PDFs were created with Photoshop.

The problem is that Photoshop stores JPEG CMYK data in PDF/EPS using "normal" values, whereas in standalone JPEGs it stores inverted values.

This makes extracted JPEGs appear inverted. Is there any way to place a marker into the extracted `.jpg` file to make Photoshop open it with the proper encoding? The process must be lossless (not involve further entropy encoding).

The JPEGs already contain the `APP14` marker, and removing it has no effect.

Below is a quote from the `libjpeg` docs:

> "... it appears that Adobe Photoshop writes inverted data in CMYK JPEG files: 0 represents 100% ink coverage, rather than 0% ink as you'd expect. ... Photoshop 3.0 [and newer]... write uninverted YCCK in EPS/JPEG files... (But the data polarity used in bare JPEG files will not change...)"