I found this on linuxquestions.org
Almost all jpegs are YCbCr, the exception are some jpegs created on an Apple Mac and Windows.
If you use the gimp, don't check the "Progressive" box. Also, subsampling must be 2x2, 1x1, 1x1 (that's what the 221111 hints at).
Than your jpeg should work.
I remade the 3 required bootsplashes using the above rules and 2 of my pictures which previously failed worded flawlessly. The
third picture would have worked as well but .jpg was capitalized as .JPG (a carryover from the name it had before). Once that was
corrected it worked as well.
So some simple rules for resizing with Gimp...
1. Don't check the "Progressive" box ( or anyother box on the left, why would you need EXIF data or thumbnails anyway)
2. Subsampling must be 2x2,1x1,1x1.
3. .jpg can't be capitalized, (I think that rule is just for me.)
4. Use the slider to reduce the file size as much as the picture quality can bear. Smaller file sizes make for faster boots, but a large file size does not seem to prevent the picture from showing. I have 1024x768 ranging from 40kb to 178kb all work.
With those rules your "Bootsplash-Theme-Creator" worked like a charm. I'll work on a screencast in the next couple of days. Thanks for this.