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Old Dec 28, 2004, 6:40 AM   #1
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Hi,

Could anyone tell me what happened to the jumper below? :? When I tried to crop it (to send just the jumper to the forum) it came out lookingfine. It also looked okay in original jpeg format, before I took it into my photo-editing prog. This post-editing version is bad, and the bigger version I did looks even more haywire.

Help would be much appreciated.

Apologies for editing off the head - but my aunt would shoot me otherwise!

abw, Canna.
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Old Dec 28, 2004, 11:01 AM   #2
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That is a moire pattern caused by having too few pixels. You get an interference pattern between the dots on the screen and the pixels in the picture with some fine patterns. It looks as though you posted a screenshot so that a resample back to a larger size doesn't remove them. But if you resample your original reduced image back to a higher pixel count the pattern will likely disappear. Not that you would want to do that for any practical reason since you won't recover the original detail, but it would be instructive to see how the patterns appear and disappear with resolution.

Some examples:
http://www.mathematik.com/Moire/
http://www.pinch.com/tweak/focus-grid.html
http://www.meko.co.uk/glossaryimages/moire1.gif





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Old Dec 30, 2004, 9:35 AM   #3
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Slipe,

Thank you tons for your help.

In fact anything I do to this pic, short of just opening the original filewith the basic XP prog, makes itgetthe moire effect very strongly. I reckon I could not have photographed the jumper at a worse angle, (other pix I tookwith thejumperinwere okay). For this pic, in the end I just selected the jumper and blurred it.

The links were interesting. The first one was so nice I've put it in favourites, to look at while I talk to people on the phone...The other links were excellent too -but I've got a lot to learn!

Thanks again for your help.

Canna.




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Old Dec 30, 2004, 9:52 AM   #4
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You don't run into it as much with higher pixel counts, but older cameras with smaller sensors often actually took the photos with moire patterns on certain fabrics. Not much you could do there except blur it like you did.
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Old Dec 31, 2004, 3:38 AM   #5
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Slipe - thanks.

Canna.
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