RETURN TO TUTORIALS SECTION
JPEG Copy Test
by Jinny Brown  e-mail

copyright 1999 - 2000, Jinny Brown 

Just for the heckuvit, and to settle an ongoing question, I opened Painter 6, then opened a small graphic and ran a JPEG copy test with it. I saved it the first time with: 
JPEG Encoding Quality set to Excellent
Quality: 100%
Smoothness: 0
Progressive JPEG box unchecked
HTML Map Options boxes all unchecked 
Then I closed the file and opened the saved copy, and repeated the save in the exact manner, but naming the file with the next available number. Continuing in this mode, I saved 60 copies of the file, each time opening the last saved file and saving it with the next available number. 

Along the way, I opened the first copy, then the 10th copy to compare them, and so on, through the complete process, about every 10 copies. By the 10th copy, I could begin to see a difference between that and the first copy and by the 60th copy, the difference was even more obvious.

From this, I conclude, that even though the JPEG file copy is saved each time using Excellent quality and all other settings are equal, the image does degrade. 

Another odd thing: The first two copies were 17 kb. All following copies were 16 kb. I wonder how long.. how many more copies.. it would take for the file size to drop to 15 kb... or was this due to some other factor and degrading files?

If those who say that JPEG quality doesn't degrade when the file is copied at the same high quality mean copying from the same original image file each time, I can understand why they say it doesn't degrade (noticeably). But when a copy is made of a copy, then another copy is made from that copy.. it is more understandable that it would degrade.. just as a paper copy made on a copy machine degrades with each "removal" from the original (once, twice removed, etc.).

Here are the 1st, 10th, 20th, 30th, 40th, 50th, and 60th copies for comparison:
 

.1st

 
10th

 
1st

 
20th

 
1st

 
30th

 
1st

 
40th

 
1st

 
50th

 
1st
60th
.
Jinny Brown, September 1, 2000
.
e-mail
copyright 1999 - 2000, Jinny Brown
.
RETURN TO TUTORIALS SECTION