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View Full Version : JPEG Artifacts: how do I get rid of these?



enduro
30-03-2009, 21:02
I only now have a jpg of this image after a recent hard drive disaster and on closer inspection I can see that there appears to be artefacts in the graduated bokeh in the lower right area which seen here as a crop.

The artefacts really show up on a print.

Do any of our guru's have ideas on how I can smooth these out without effecting the rest of the images. I assume I will need to use a layer at some point and I would prefer to be able to just brush in the adjusted layer for the BG and keep what is left of the image quality intact.

Thank you for your assistance,

Wayne.






http://members.iinet.net.au/%7Edamask/Wayne/Photo/forum/canon/artifact_crop.jpg

ricktas
30-03-2009, 21:13
have you tried making a selection of the area, feathering it and applying a bit of blur, Wayne. Not something I have had to deal with, so this is just a guess at something that might work!

Tannin
30-03-2009, 21:17
Looks to me like the same problem I've been struggling with lately, Wayne. I don't think these are actually JPG artifacts per se, they are the result of colour compression - fitting the very large number of colours in the original scene into a much smaller number of colours. JPGs do this, of course, but you can get exactly the same sort of problem with any other file format when you have a small enough number of colours - PNG for example, or even TIFF.

This happens all over the image, but you can only see it when there is (a) no other detail to mask it (such as plumage), (b) not a lot of noise (random noise masks it well), and (c) enough colour graduation for the effect to show.

Printers (as I recall) don't have as fine a control over colour as a good screen does, so it's reasonable to expect problems when printing.

One of the causitive factors is an uneven histogram. You can start with a picture that is perfectly OK and make a JPG no worries. Then apply some PP that changes the histogram (curves, levels, shadow/highlight, even noise reduction in some cases) and make a second JPG. BAM! The problem is there.

I assume that it's worse again when you put the image through conversion to a different colourspace - which is exactly wht happens when you print, of course.

The cure is to return to the original image and do your PP differently ... if you can! Otherwise, you have to do some heavy-duty Photoshop stuff ..... which is the point at which my slender river of knowledge dries up and fades gently away into the sand. :(

Izy
30-03-2009, 21:17
possibly look at taking the steps usually using in 'airbrushing a model'?

I always have to follow the tut's can never remember the steps :p

enduro
30-03-2009, 21:28
Looks to me like the same problem I've been struggling with lately, Wayne. I don't think these are actually JPG artifacts per se, they are the result of colour compression - fitting the very large number of colours in the original scene into a much smaller number of colours. JPGs do this, of course, but you can get exactly the same sort of problem with any other file format when you have a small enough number of colours - PNG for example, or even TIFF.

This happens all over the image, but you can only see it when there is (a) no other detail to mask it (such as plumage), (b) not a lot of noise (random noise masks it well), and (c) enough colour graduation for the effect to show.

Printers (as I recall) don't have as fine a control over colour as a good screen does, so it's reasonable to expect problems when printing.

One of the causitive factors is an uneven histogram. You can start with a picture that is perfectly OK and make a JPG no worries. Then apply some PP that changes the histogram (curves, levels, shadow/highlight, even noise reduction in some cases) and make a second JPG. BAM! The problem is there.

I assume that it's worse again when you put the image through conversion to a different colourspace - which is exactly wht happens when you print, of course.

The cure is to return to the original image and do your PP differently ... if you can! Otherwise, you have to do some heavy-duty Photoshop stuff ..... which is the point at which my slender river of knowledge dries up and fades gently away into the sand. :(

thanks ppl.

I only have a high res jpeg image. The original RAW and later TIFF went into the ether with that hard drive.

Looks like a series of steps might eb to do a noise reduction to smooth the area out and then apply a healing brush an layer the original subject in.

Izy
30-03-2009, 21:59
don't forget to add noise back into the healed area

smorter
31-03-2009, 01:05
Shot is quite noisy, but if you had a cleaner shot it makes it much easier to smooth the background. Here's a 1min attempt, it's a bit sloppy but hopefully the point is clear. This was layer masked gaussian blur
http://dawei.zenfolio.com/img/v7/p1028503980-5.jpg

This posterization is nasty...one of the advantages of RAW is you get a bit more leeway

enduro
31-03-2009, 10:25
Shot is quite noisy, but if you had a cleaner shot it makes it much easier to smooth the background. Here's a 1min attempt, it's a bit sloppy but hopefully the point is clear. This was layer masked gaussian blur


This posterization is nasty...one of the advantages of RAW is you get a bit more leeway

thanks smorter,

I'll have a go at that tonight.