[robski]

In my last posting the utility program compared the original tiff against various saved Jpeg versions. After a small modification to the program I was able to flag the offending pixels. A blue flag for pixels that errored by less than 2%. A green flag for those that errored between 2% and 10%. A red flag for those with an error of more than 10%. Error pixels are often referred to as Jpeg artifacts. See attached.

When the Jpeg Committee were considering various lossy compression schemes they took into account which scheme gave the best results for the type of images they wanted to handle. You may have been wondering why I had designed such an odd looking test image. I wanted to contrast gentle undulations with steep steps in levels running vertically, horizontally and diagonally. If you examine the Jpeg versions you will notice that the errors congregate around the steep steps especially those that run diagonally. This falls inline with the decisions made by the committee.

The point I am trying to make is that gentle undulating data is more suitable for Jpeg compression than black and white line art images or black text on a white background. This then leads into the subject matter of whether we should shoot in raw (Tiff) or Jpeg along with what Post Processing image storage formats we should used. It is not my intention to go down this avenue as it is a topic more than adequately covered elsewhere.