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#1
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JPEG degradation
I was reading a photography book by Bryan Peterson and he says something in
it I never knew. He said that opening JPEG's over and over........with time they will degrade to the point to where they dont open anymore. My question is, if on a screen saver you are doing a slide show with all the pictures that you took, does this count as 'opening' and 'closing' of a JPEG and will those degrade over time? |
#2
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JPEG degradation
In "TSKO"
wrote: I was reading a photography book by Bryan Peterson and he says something in it I never knew. He said that opening JPEG's over and over........with time they will degrade to the point to where they dont open anymore. That's only possible if you re-save the file after changing it somehow. Simply opening the file to view it and then closing it without writing to it will not change the file. If the viewing software you're using always re-writes the file whenever you open it for simple viewing, toss it and get something else. -- Bert Hyman St. Paul, MN |
#3
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JPEG degradation
If they are opened and not RE-SAVED, there should be no problem,
I believe. I was reading a photography book by Bryan Peterson and he says something in it I never knew. He said that opening JPEG's over and over........with time they will degrade to the point to where they dont open anymore. My question is, if on a screen saver you are doing a slide show with all the pictures that you took, does this count as 'opening' and 'closing' of a JPEG and will those degrade over time? |
#4
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JPEG degradation
On Thu, 25 Jan 2007 19:36:14 -0500, "TSKO" wrote:
I was reading a photography book by Bryan Peterson and he says something in it I never knew. He said that opening JPEG's over and over........with time they will degrade to the point to where they dont open anymore. My question is, if on a screen saver you are doing a slide show with all the pictures that you took, does this count as 'opening' and 'closing' of a JPEG and will those degrade over time? That doesn't make sense to me. Perhaps he meant that opening /and saving/ a JPG multiple times incrementally degrades the image quality. It seems to me that simply displaying an image should do nothing whatsoever to the source file. |
#5
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JPEG degradation
On Thu, 25 Jan 2007 19:36:14 -0500, TSKO wrote:
I was reading a photography book by Bryan Peterson and he says something in it I never knew. He said that opening JPEG's over and over........with time they will degrade to the point to where they dont open anymore. My question is, if on a screen saver you are doing a slide show with all the pictures that you took, does this count as 'opening' and 'closing' of a JPEG and will those degrade over time? What happens is that every time you SAVE a jpeg image it is recompressed. There was already some degradation the last time it was SAVED or created, so it gets worse. It does not matter in the least how many times you open the file. |
#6
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JPEG degradation
On Fri, 26 Jan 2007 00:43:26 +0000, Bert Hyman wrote:
In "TSKO" wrote: I was reading a photography book by Bryan Peterson and he says something in it I never knew. He said that opening JPEG's over and over........with time they will degrade to the point to where they dont open anymore. That's only possible if you re-save the file after changing it somehow. Matters not an iota if you change it or not. Saving it will always cause additional degredation. Simply opening the file to view it and then closing it without writing to it will not change the file. If the viewing software you're using always re-writes the file whenever you open it for simple viewing, toss it and get something else. |
#7
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JPEG degradation
On Thu, 25 Jan 2007 18:27:24 -0700, ray wrote:
On Fri, 26 Jan 2007 00:43:26 +0000, Bert Hyman wrote: In "TSKO" wrote: I was reading a photography book by Bryan Peterson and he says something in it I never knew. He said that opening JPEG's over and over........with time they will degrade to the point to where they dont open anymore. That's only possible if you re-save the file after changing it somehow. Matters not an iota if you change it or not. Saving it will always cause additional degredation. Opening the file to view it doesn't requiring it be saved again. You should shut the **** up about matters for which you haven't the slightest understanding. |
#8
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JPEG degradation
In news
wrote:
On Fri, 26 Jan 2007 00:43:26 +0000, Bert Hyman wrote: In "TSKO" wrote: I was reading a photography book by Bryan Peterson and he says something in it I never knew. He said that opening JPEG's over and over........with time they will degrade to the point to where they dont open anymore. That's only possible if you re-save the file after changing it somehow. Matters not an iota if you change it or not. Saving it will always cause additional degredation. Why? If the app re-writes the same series of bytes back onto disk that it read, there will be no change in the file or the resulting image. -- Bert Hyman St. Paul, MN |
#9
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JPEG degradation
TSKO wrote:
I was reading a photography book by Bryan Peterson and he says something in it I never knew. He said that opening JPEG's over and over........with time they will degrade to the point to where they dont open anymore. This is nonsense. Opening the file doesn't change the file. This is trivially easy to demonstrate using file-compare programs. My question is, if on a screen saver you are doing a slide show with all the pictures that you took, does this count as 'opening' and 'closing' of a JPEG and will those degrade over time? No. The situation that's an issue is when you open, change, and *save* the jpeg. It goes through and re-compresses it again, and because there are changes, some of the damage this time is *different* from the damage the first time. (I say "damage"; jpeg is a lossy compression format, that's how it gets such small file sizes.) |
#10
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JPEG degradation
Matters not an iota if you change it or not. Saving it will
always cause additional degredation. Why? If the app re-writes the same series of bytes back onto disk that it read, there will be no change in the file or the resulting image. I think in almost all cases, it does cause degredation. At least it seems that way to me based on my own experience. JPG is not quite like MP3 audio, which while lossless, works on specific frequencies at a given bit depth. Say you have an MP3 sound file and convert it to 32 kbps, 16 bit, 22 khz Mono. If you use the same program to encode, it should use the same methodology, which would include eliminating certain very high and very low frequencies, always according to the same formula. When processing, no new frequencies are introduced that can be eliminated later, I believe. But with JPG, each time you save the file, the entire image is altered, and each time it is edited, the entire image is processed and saved. It's not limited to specific "colors" or a range of pixels in specific areas, I believe, so degredation always occurs. |
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