Output image file quality / JPEG artifacts

Standard Test Scene
In JPEG output mode the EOS-1Ds Mark II provides four different image sizes as follows:

  • 4992 x 3328 (L) - 16.6 million pixels
  • 3600 x 2400 (M1) - 8.6 million pixels
  • 3072 x 2048 (M2) - 6.3 million pixels
  • 2496 x 1664 (S) - 4.2 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 4.0 and 7.0 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 14 MB per image), the Mark II uses the newer .CR2 RAW file format.

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 1.2.

Full resolution, different quality levels

4992 x 3328 RAW (not for download)
15,368 KB .CR2
4992 x 3328 (L) JPEG Quality 10
9,896 KB
4992 x 3328 (L) JPEG Quality 8 (default)
5,412 KB
4992 x 3328 (L) JPEG Quality 6
3,801 KB
4992 x 3328 (L) JPEG Quality 4
2,653 KB
4992 x 3328 (L) JPEG Quality 2
1,765 KB

Everything fom 9.7 MB to 1.7 MB representing the same 16.6 megapixels, and what's most surprising is that at the highest compression settings its still difficult to make out any JPEG compression artifacts. Most people will no doubt leave the JPEG quality at the default setting of 8, however there really doesn't seem to be much harm in dropping down to quality 6 if storage space is tight.

Smaller image sizes

3600 x 2400 (M1) JPEG Quality 8 (default)
3,123 KB
3072 x 2048 (M2) JPEG Quality 8 (default)
2,443 KB
2496 x 1664 (S) JPEG Quality 8 (default)
1,745 KB

A high quality downsampling algorithm means clean crisp looking smaller size images.