 Posted 5/9/2008 6:27:52 AM
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A term I use a lot when offering suggestions for improvement on images is the presence of "JPG Compression Artifacts". A surprising number of members and users write me back to ask, "What this that?"
The image below shows a lot of JPG artifacts. Can you see them? Sometimes I wonder if it's my monitor or my eyes. If you ever see this kind of thing on my images, you should give me a very low score.
The creation of these artifacts must be avoided in postprocessing. There are a lot of causes of JPG artifacts....
1. Saving at a low quality JPG quality. Save at 100% quality!
2. Every time you "save as..." a JPG format file, you will lose 3% of your image quality. Multiple saves degrades quality cumulatively.
3. Oversharpening is always a culprit.
4. Resizing up beyond the available pixels can create artifacts, as the application attempts to interpolate pixels.
To avoid JPG artifacts you can work with RAW files or TIFF or PSD format files during postprocessing. Only during the last step prior to upload to the contest should you convert to a JPG file format. If your camera can only capture JPG format files, then work with the largest and highest resolution file your camera can capture. Compact Flash (CF) cards have much more capacity these days and are much less expensive than they used to be. No reason to capture anything less than top quality images for CF card space conservation purposes.
Some noise reduction applications can reduce JPG artifacts, but usually at the expense of loss of image detail. Better to avoid creating the artifacts in the first place.
Okay, probably things you already knew. But, it is surprising to me how often I see JPG artifact distractions on images in the contest. If participants could avoid these distractions, I'd offer much better scores on their images.
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Posted 5/9/2008 1:45:59 PM
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| Everytime you save as it will lose 3% is there another way around this?
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Posted 5/9/2008 3:11:02 PM
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I saw this photo the other day (I don't know whose it is), and it looked pretty good until you looked at it at full size. The artifacts had kind of a strange shape to them, so I wasn't absolutely sure what I was seeing. It's a good example of what will happen if you have any problems with the original and you load at larger than 640X on the long side. For what it's worth, I really liked the composition of this photo.
Go when you can, go where you can, shoot what you can
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