How Bad is JPEG?

Rex Waygood Fordingbridge Camera Club 2005

The Often Stated

• JPEG is a lossy compression technique

• Information is lost in saving• Do not use JPEG for repeated

saving• Do not use JPEG for editing

The Truth?

• If you do not alter the image or the JPEG Algorithm successive saves do little or nothing. (Compression at minimum)

• Example 15,111kb Tiff image• Multiple JPEG save, read, save• 3,472kb;3,489kb;3,500kb;3.506kb;3,509

kb;3,510kb;3,510kb;3,511kb• Note the file size does not continue to

reduce

Why?

• The JPEG Algorithm looks at small areas of the image and performs a compression routine. Doing it again does nothing/little.

• Ever tried zipping up a zipped up file?

This is the first JPEG from the ‘original’ TIFF

Let’s look at that Chap’s Watch

From the TIFF

From First JPEG

From Eighth JPEG

This is the watch from the previous image. The whole image was saved as a JPEG and then read again. The watch was cropped out and saved as a TIFF. The process was repeated and as can be seen there is little to no degradation of the image.As has been shown with the file size something is happening but certainly not a continuation of data loss.

My software was set up for 0 compression and zero smoothing. Note it did take the TIFF from 15Mb to 3.5Mb jpg!!!!!!

And the Final 8th JPEG

Well that experiment didn’t count!

• Because I didn’t change anything• So I am going to do a big edit• Then I am going to do a JPEG save• Then I will re-read the image• Then I will do a big edit, JPEG save• Etc. until I get bored

Is that a big enough Edit? Then saved as a JPEG.

This was the Next Edit! Put it back again!

This was done 6 Times

From the original TIFF

From the sixth JPEG

As can be seen there is little or no degradation, again.

Cheating Again!

• The watch is a fair way away from the edit

• As the JPEG Algorithm works in small areas the edit is too far away from the watch.

• Show us some thing near the edit!

OK Then!

From the original TIFF

From the sixth JPEG

The dark line is where at some point I was One pixel out! It is the border of the Edit.

Conclusion

• Successive saves to a JPEG image with constant settings do not continue to create loss and degrade the image.

• Editing and saving does not produce dire effects in image quality

• JPEG is unjustly criticised.• Just make sure you know what you

are doing!