Jpeg Artifacts

[spl]

I am trying to teach myself to identify jpeg artifacts. Having read some stuff on the web I can't decide whether this one has them or not. If it does I would say they were only slight. I blew the pic up to 400% and looked on the sky area and found some darker blue blocks but I don't think any of them were as big as 8X8 pixels which some sites say is the typical size and there didn't seem to be any of these kind of reversed gradients within the blocks that appear in the demos I have seen. I would be interested to hear what others think and any further information about the best way to know for sure that they are there. A lot of the pics I took on this particular day left me with no doubt that they were affected so although this one seemed a bit better than the rest I suspect it may also have lurgies

[Ian]

Re: Jpeg Artifacts

I am trying to teach myself to identify jpeg artifacts. Having read some stuff on the web I can't decide whether this one has them or not. If it does I would say they were only slight. I blew the pic up to 400% and looked on the sky area and found some darker blue blocks but I don't think any of them were as big as 8X8 pixels which some sites say is the typical size and there didn't seem to be any of these kind of reversed gradients within the blocks that appear in the demos I have seen. I would be interested to hear what others think and any further information about the best way to know for sure that they are there. A lot of the pics I took on this particular day left me with no doubt that they were affected so although this one seemed a bit better than the rest I suspect it may also have lurgies

Any bumpiness in the structure of the blue areas of your sky are most likely to be sensor noise. Blue is generally the noisiest colour channel by nature. It's easily fixed by doing a feathered selection of the area and using something like a noise reduction function or gaussian blur to smooth things out. Experminentation is the key!

Ian