Re: Compare image levels?
Re: Compare image levels?
- Subject: Re: Compare image levels?
- From: Chris Williams <email@hidden>
- Date: Mon, 26 Nov 2007 16:43:59 -0800
- Thread-topic: Compare image levels?
Image comparison is a very, very complex subject. It has been the subject
of more than a few CompSci PhD theses. So, a short answer is difficult.
However, picture data is just data. A byte (more or less) for Red, one for
Green, one for Blue, etc. (if in RGB). You can access the data in an
NSBitmapImageRep and have at it.
You will soon, however, realize that this is really hard. Compression
algorithms mess with the data "just a little bit" to get better results, and
that throws off comparisons. Pictures get cropped and that makes them just
a bit different. And so on. Comparing strictly numerically almost never
works.
However, as a starting point, you might consider looking at the project:
> From: Brendan Wilde <email@hidden>
> Date: Tue, 27 Nov 2007 11:23:26 +1100
> To: <email@hidden>
> Subject: Compare image levels?
>
> I am trying to find a way to compare images based on colour etc.
> If I am using Photoshop I can use it doing the levels or historyogram
> and then visually compare the information. I am wondering if I can
> somehow do this programmatically?
>
> The idea is compare two images and check if they are the same or
> similiar
> based on their levels possibly comparing to a range of levels to find
> a match.
>
> Can anyone give me a starting point?
> Thanks
> Brendan
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