[robski]

I am sure many of you have wondered how Tiff compares to Best Quality Jpeg Setting. Well lets say from the outset that Best Quality setting is not normally the Best Possible setting that could be used. The Application programmer has restricted you to a setting that optimizes compression ratio against little or no perceived loss in image quality. Accordingly applications of different versions and from different vendors will have a slight variance in compression ration and image quality. It's really down to what values they decide to use in their quantization tables.


In this post I am attempting to illustrate the difference between tiff and PhotoShop setting of 12, 9 and 5 within the limitations of using Jpeg attachments.

The first attachment compares the histograms of a tiff image and saved as Jpeg versions at settings of 12 (max quality) , 9 ( high quality ) and 5 ( medium quality ). The tiff histogram shows some very distinct and well defined areas of brightness levels in the image. The Jpeg max quality shows some deviation from the original tiff. The differences are there but not huge. Basically a number of pixels have slightly change their value. As the compression levels are increased to 9 and 5 a greater variance can be seen.

The second attachment is the image in question.

Next I took the original tiff file and subtracted the Jpeg version from it to produce a difference image. As the differences were lost in the darkness I then increased the brightness by 50%. I also show the histogram for each case.

With the setting of 12 the differences are barely noticeable and you have to amplify the image to make out which pixels differ.

With the setting of 9 and 5 the differences become more noticeable.