Output image file quality / JPEG artifacts

Standard Test Scene

In JPEG output mode the Mark II provides four different image sizes as follows:

• 3504 x 2336 (L) - 8.2 million pixels
• 3104 x 2072 (M1) - 6.4 million pixels
• 2544 x 1696 (M2) - 4.3 million pixels
• 1728 x 1152 (S) - 2.0 million pixels

You can control the JPEG quality level used for each image size via the record menu, quality levels range from 10 (low compression, high quality, large file size) to 1 (high compression, low quality, small file size). The default quality level is 8 which produces fairly large images with no visible JPEG artifacts (between 2.5 and 3.0 MB per image at large size). In addition of course the Mark II also provides a RAW capture mode which in effect dumps the RAW data direct from the CMOS sensor into a losslessly compressed file (around 9.2 MB per image). With the introduction of the Mark II Canon has removed the confusion over the use of the .TIF file extension on RAW files and now uses the .CR2 file extension.

Below you will find crops of the same 240 x 180 portion of the center of a sequence of images taken at some of the available combinations of image size and quality. Crops shown are at 100%, saved as extremely high quality JPEG. The RAW file was converted to a TIFF using Canon EOS Viewer Utility 1.0.

Settings: ISO 200, Canon EF 24-70 mm F2.8L, Parameters: Shp+2, Color Matrix: Standard

Full resolution, different quality levels

3504 x 2336 RAW (Uncompressed) 9,530 KB .CR2 (not for download)	3504 x 2336 (L) JPEG Quality 10 5,584 KB .JPG
3504 x 2336 (L) JPEG Quality 8 (default) 3,194 KB .JPG	3504 x 2336 (L) JPEG Quality 6 2,523 KB .JPG
3504 x 2336 (L) JPEG Quality 4 1,833 KB .JPG	3504 x 2336 (L) JPEG Quality 2 1,287 KB .JPG

What's surprising here is that even at the higher compression levels (quality 4 and quality 2) it's quite difficult to see any visible JPEG artifacts at 100% view. This points to the use of a high quality JPEG compression algorithm. The use of a higher compression level could be important for transmission of images over wireless or other low speed connections.

Smaller image sizes

3104 x 2072 (M1) JPEG Quality 8 (default) 2,496 KB .JPG	2544 x 1696 (M2) JPEG Quality 8 (default) 1,847 KB .JPG
1728 x 1152 (S) JPEG Quality 8 (default) 1,016 KB .JPG

As expected the Mark II's downsampling interpolation is very good, nice clean aliasing with no noticeable 'jaggies'. Reducing image size also increases buffer space and the number of images which can be shot in a burst, in our tests we could capture 70 frames in a 8.3 fps burst at the M2 image size (4.3 million pixels).