Jpeg quality reduction?
- Thread starter Vass
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- Bob
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Have a gander here: http://graphicssoft.about.com/od/formatsjpeg/a/jpegmythsfacts.htm
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- Dan
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The quality loss comes from the compression. If you keep opening a photo and editing it, then re-saving it again, there will be a loss in quality. Obviously saving at maximum JPEG quality each time will compress with less quality loss than if it is saved with maximum compression.
Hope this explains it!
Hope this explains it!
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It's about compression.
In a tif or psd filethe compression is lossless.
In a jpg file it's lossy compression so your image will deteriorate. When saving a jpg you can set the amount of compression. Save an image at 1 or at 12 and see what the difference is.
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- Matt
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If you simply copy the file using the file system you won't get any degradation. As you suggest, in that case you are simply copying 1's and 0's.
The loss in quality comes when running the jpg compression algorithm which happens when saving from an image editor. This is because the jpg format throws out some image data each time it saves in order to compress the file and save space.
This can often cause some confusion about exactly when jpg images get damaged and what you should or shouldn't do with them to minimise this. If you open a jpg, edit it, save it, close it and repeat this cycle you will eventually introduce noticeable damage (how quickly depends on your compression settings).
However, you won't get an incremental loss of quality if you keep saving the same file during an editing session (as a precaution against the computer crashing for example) as long as you don't close and re-open the file each time. This is because whilst the jpg algorithm is applied to the new saved file, it isn't applied to the in-memory copy of the image and therefore no damage is caused to this. Effectively when you make your final save and close the file you will have applied only one round of the jpg algorithm to the final file on disk.
The loss in quality comes when running the jpg compression algorithm which happens when saving from an image editor. This is because the jpg format throws out some image data each time it saves in order to compress the file and save space.
This can often cause some confusion about exactly when jpg images get damaged and what you should or shouldn't do with them to minimise this. If you open a jpg, edit it, save it, close it and repeat this cycle you will eventually introduce noticeable damage (how quickly depends on your compression settings).
However, you won't get an incremental loss of quality if you keep saving the same file during an editing session (as a precaution against the computer crashing for example) as long as you don't close and re-open the file each time. This is because whilst the jpg algorithm is applied to the new saved file, it isn't applied to the in-memory copy of the image and therefore no damage is caused to this. Effectively when you make your final save and close the file you will have applied only one round of the jpg algorithm to the final file on disk.
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Shoot RAW, edit that and output that final image as a jpg.
OP
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- Mark
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that makes sense folks, many thanks
I was aware club competitions, the file gets copied from place to place before it finally hits the projector, so was concerned about quality
but as you rightly say, so long as its a direct copy, there is nothing to worry about.
I was aware club competitions, the file gets copied from place to place before it finally hits the projector, so was concerned about quality
but as you rightly say, so long as its a direct copy, there is nothing to worry about.