Mike Chaney's Tech Corner

I did some conversions from RAW format to TIFF and JPEG (at several different quality settings) with three different programs (QU, Irfanview, and Photoshop) and I notice that the JPEGs from QU with the highest quality setting are much larger than with the other programs.  Here is a table of results (file sizes in kb):

                       QU          Irfanview         (Photoshop)
TIFF                 26,450    26,448             26,765
JPG-100 (12)    11,858    5,736               6,113
JPG-90 (11)      2,277      1,533               2,571
JPG-80 (10)      1,462      957                  1,406

While at the lower quality settings, the file sizes are about the same (1-2.5 Mb), at the highest quality setting the QU JPEG is twice as large as the other two.  TIFFS are approximately the same size, so why such big JPEGS from QU with the quality set at "100"?

I believe the answer is in the ideal JPG at 100% Lowest/least compression for least compromise in quality. (No Artifacts)
Also affording the greatest flexibility in size when creating the jog.

Fred

Notice that the size is comparable to PS up to 90%.  The size in QU will be comparable to PS up to 94% and will then increase from 95 to 100%.  That's because QU maximizes quality from 95 to 100% by using single pixel subsampling.  Most software uses 2x2 or 4x4 subsampling which can (in certain areas) create square blocks when you look at the image at higher magnification.  Using 1x1 ensures that there is no JPEG blocking.  So if you want maximum quality but with the most compression possible without blocking, use 95% in QU.  If you want it to give a smaller size, use 94% or lower.  I added that feature some years ago so that users can save JPEG's that are visually indistinguishable from TIFF's or other lossless formats but still have the compression of JPEG.  This is also how QU is able to cache raw files with pixel level accuracy.

Mike