Detect/filter out overcompressed photos?

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Detect/filter out overcompressed photos?

Postby spycam » Sun Oct 02, 2011 10:58 pm

Well, I'm sorry, i didn't know which subforum to ask that on, so mods can move it to where it belongs.

Now I just wanted to ask if anyone by chance knows any available software or freeware that could scan a photo collection and list the overcompressed ones?
You know, overcompressed photos are the ones with JPEG compression artifacts sometimes called pixelation, especially on the edges, then the washed out/blurry photos...

I mean there should be some criteria that could make the filtering possible, maybe something like compression factor of bytes per pixel or something else?

Do you know such?
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Re: Detect/filter out overcompressed photos?

Postby spycam » Mon Oct 03, 2011 3:57 pm

Anyone?
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Re: Detect/filter out overcompressed photos?

Postby pfaffenbichler » Tue Oct 04, 2011 8:01 am

I don’t know any such software.

One can check the JPG-setting via Script, but that does not mean the image may not intermediately have been saved with worse compressions; and the compression factor itself may be misleading with certain images.

May I ask what the background for your inquiry is?
How voluminous is that collection, are there many sources, …?
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Re: Detect/filter out overcompressed photos?

Postby spycam » Tue Oct 04, 2011 11:26 am

Well,
i have around 40k photos. I wanted to start hand sorting them but thought to remove bad quality - overcompressed ones at first, so less sorting will be done.
The collection consists of a lot of photos collected for a long while from facebook and other social networks, mostly photos that relatives and friends used to post there, some old photos from school and college times, etc.
Then there are some part of funny/weird photos that we all use to send by email and other ways.
These were bigger part of sources, and there are are some other photos i found when i was scanning my old HDs ;)
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Re: Detect/filter out overcompressed photos?

Postby dieki_n » Tue Oct 18, 2011 8:56 pm

I once detected blurry photos from a set of 2k by running "Find Edges" and then looking at a histogram; the blurrier the photo, the less edges it has, so the brighter it's histogram is.

Now, the blockiness from JPEG compression is always in 8px blocks; so you could do a similar thing by finding edges, then selecting the pixels at the edges of 8px wide blocks. The darker those spots are, the more blocks it has, so the higher it's compression is. Watch for false positives, though. :)
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