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I was wondering if there are any freeware that is able to judge the quality of a photo (can be a jpeg or raw format) and give a score to it?

I kind of sick of comparing photo taken by different camera but on the same item as I need to zoom and examine closely to determine the quality.

From what I know, a image quality can be determine by many factors such as histogram and the ISO used.

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Surely this is subjective. You would not want to judge the quality of a photo solely by technical attributes alone. Sometimes solid blacks or blown highlights can really make a photo (especially in B&W photography)... –  Mike Jun 15 '12 at 14:33
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@Mike, Thanks Mike, so are there any software that can judge the photo solely by technical attributes? –  Jack Point and Shoot Jun 15 '12 at 14:43
    
I don't know. Sorry. –  Mike Jun 15 '12 at 14:51
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I would also like to submit for consideration the idea that if you have to zoom in and examine closely to compare image quality from two cameras, they are both good enough and you should consider other factors in making your decision between those two cameras. –  mattdm Jun 15 '12 at 15:13
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3 Answers

For video, the Gspot freeware information tool includes a 'QF' quality figure. This is calculated from:

(video bitrate in bits/second) / (horizontal res * vertical res * framerate)

It seems to me that File size / (horizontal res * vertical res) would give a similar rough measure for jpegs.

What do you think?

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Not really. This is an entirely different concept of "quality". With video, there's just so much data that high compression is unavoidable (at least with today's storage and networks). With images, size is important to some degree, but generally we try to compress no more than the point where no compression artifacts are perceivable. This varies greatly depending on the size of an image -- a pattern with smooth (but unsubtle) color transitions will be much more compressible than one with a lot of busy, fine detail. –  mattdm Nov 28 '13 at 3:13
    
And of course, the question mentions RAW, where files are compressed losslessly. There, it's the same -- more detail makes bigger files, but not necessarily better quality in any sense of the word. –  mattdm Nov 28 '13 at 3:14
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I don't see how you could judge image quality from histogram and ISO, it would totally miss whether or not the image is in focus.

I don't know of any objective metric for measuring quality. Period. Its a philosophical question: what is quality?

GIMP and Darktable are free, open source programs that will let you look at the images and use your eyes and your brain to judge quality. Darktable has ratings much like Aperture and Lightroom.

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I don't think there is any software that does what you say exactly in the way that you want it. But if you can relax your requirements a little there is something that may work for you.

Instead of just looking at a single image and giving it a score, let's say you have a golden image, one that you have inspected in every way and you consider it the best it can be for its class.

Now you can compare other images of the same subject (with same focal length, same exposure, etc.) and get a score for how close the new images are to the golden one. For example, you could use this technique to objectively measure how much the JPEG compression degraded an image, using the equivalent raw image as your golden image. (note that I said objective, this algorithm does not take into account subjective aspects of a comparison, so it isn't sometimes an indication of perceived quality).

The algorithm is called Peak signal-to-noise ratio or PSNR in short. There are several open source implementations of this algorithm. OpenCV and FFmpeg have them, this question at stackoverflow.com lists a few more.

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