jpeg deterioration
Nov 28, 2017 03:00:16 #
RWR
Loc: La Mesa, CA
Fotoartist wrote:
Can you show us a comparison of this degradation in 20 steps? I've never seen one. You hear this all the time but you never see the evidence.
Someone demonstrated it here two or three years ago. I don’t recall the details, but the file size decreased each time the jpeg was opened and saved. So some information was thrown away each time.
Nov 28, 2017 03:11:35 #
bsprague wrote:
If you expose JPEGs to light, they fade over time.
Doesn’t that depend on how you’re viewing them?
Nov 28, 2017 03:14:38 #
RWR wrote:
Someone demonstrated it here two or three years ago. I don’t recall the details, but the file size decreased each time the jpeg was opened and saved. So some information was thrown away each time.
The operative word here is “saved”; there is no loss if the file is simply closed. The OP needs to find out if his screensaver is saved every time the computer is shut down.
Nov 28, 2017 04:42:43 #
RWR
Loc: La Mesa, CA
BHC wrote:
The operative word here is “saved”; there is no loss if the file is simply closed. The OP needs to find out if his screensaver is saved every time the computer is shut down.
Sure, but unless the file was changed somehow, there would be no need to save.
Nov 28, 2017 05:15:10 #
RWR wrote:
Sure, but unless the file was changed somehow, there would be no need to save.
Of course there would be no need to save it. Tell that to the programmers that write the code to save whatever is on the screen at shutdown, even if only the screensaver is on the monitor, and then give the option of starting up from the screensaver or starting up from the saved files.
Nov 28, 2017 05:25:24 #
AdanteGuy wrote:
Do jpeg images deteriorate when used as a screensaver on a computer?
When they are opened, modified, and saved, they theoretically lose some quality. I experimented with that idea and changed and saved a JPEG over one hundred times. I couldn't see any deterioration at all.
https://www.thoughtco.com/jpeg-myths-and-facts-1701548
Nov 28, 2017 06:17:50 #
Fotoartist When you understand how JPEG compression works you will see that repeated change and save operations cannot fail to degrade the image. You can easily create your own evidence. Copy and save one of your own jpeg files. Rename it so there is no danger of losing your image. Now alter it in some small way and save it. Open/alter/save it ten times. Now compare it to your original image. Compare the 'new' and original versions at full scale and see the changes. Look for 'blocky' colour areas where the soft tones have disappeared and areas where details have disappeared or blurred.
Nov 28, 2017 06:21:15 #
jerryc41 I have done the same when giving talks at camera clubs and it prove to be convincing evidence of how the images degrade. Maybe the ocean between us makes the difference?
Nov 28, 2017 06:27:40 #
bsprague wrote:
Which is correct. Screensavers read the file. In theory if you are editing JPEGs and save it multiple times there will be some degrading as the software "freshens" the compression. A fun exercise is to try it. Start with an original. Save it as Version 2. Open Version 2 and save it as Version 3. Repeat. When you get to about 20, compare it to the original.
There is a difference between opening and re-saving, and opening, viewing and closing. There should be no deterioration when opening, viewing and closing.
Nov 28, 2017 06:42:09 #
Fotoartist wrote:
I've yet to see a comparison of before and after showing this degradation under normal use. It exists in theory but I haven't seen it in reality. I'm waiting for the evidence.
Nov 28, 2017 07:39:45 #
Fotoartist wrote:
I've yet to see a comparison of before and after showing this degradation under normal use. It exists in theory but I haven't seen it in reality. I'm waiting for the evidence.
I don't have a real life example to show you but I experienced it in the past while using Photoshop to make changes. It took many times opening and closing the file (and making changes) but the degradation was real and significant. Today with the non destructive filters it may not be a problem.
Nov 28, 2017 07:44:43 #
TomV
Loc: Annapolis, Maryland
When you open a file for viewing in a screen saver you are pulling in a COPY of the original and displaying it. When you decide to close it when you are done viewing it, the COPY is thrown away by the program, not saved in any fashion. The original file is not modified as a result of opening it, it stayed on your disc. Thus, when you open the file again you are COPYing the original file, not the COPY that was previously opened and somehow modified, because the file was tossed, not saved.
Nov 28, 2017 07:49:49 #
Nov 28, 2017 08:14:42 #
AdanteGuy wrote:
Do jpeg images deteriorate when used as a screensaver on a computer?
No. They are a digital medium. If you repeatedly resave them they will deteriorate because each save throws away data in the compression. But just having it reside on your computer means they are only repeatedly opened, not resaved.
Nov 28, 2017 08:40:11 #
"No, they do not degrade when viewed. The only time they degrade is when opened, changed, then saved again and again. To view them does nothing to them."
In total agreement. An original JPEG can be opened and worked with then saved several times and it is not easy for the eye to note the degradation. Modern JPEG files are of excellent quality when saved at low compression and when I do that I usually go to a TIFF because it becomes a lossless file.
There is the general misconception that a JPEG is a format that serious photographers should not use and I could not disagree more. I know of a well respected wedding photographer in this Miami area that only shoots JPEG images and NEVER ever any of her customers complained of poor quality when she delivered the photographs.
I shoot both files depending on the subject and I am pleased with the quality of my JPEG images. Tons of manipulations are available with modern editing softwares.
In total agreement. An original JPEG can be opened and worked with then saved several times and it is not easy for the eye to note the degradation. Modern JPEG files are of excellent quality when saved at low compression and when I do that I usually go to a TIFF because it becomes a lossless file.
There is the general misconception that a JPEG is a format that serious photographers should not use and I could not disagree more. I know of a well respected wedding photographer in this Miami area that only shoots JPEG images and NEVER ever any of her customers complained of poor quality when she delivered the photographs.
I shoot both files depending on the subject and I am pleased with the quality of my JPEG images. Tons of manipulations are available with modern editing softwares.
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