Presentation on theme: "How Bad is JPEG? Rex Waygood Fordingbridge Camera Club 2005."— Presentation transcript:
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;3,509kb;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?
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!!!!!!
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 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!