Imaging Question: How to determine image quality?

Question

I am looking for ways to determine the quality of a photograph (jpg). The first thing that occurred to me was to compare the file size with the number of pixels stored inside. Are there other ways, for example, to check the amount of noise in jpg? Does anyone have a good read link on this topic or any experience? By the way, the project I'm working on is written in C # (.net 3.5), and I use Aurigma Graphics Mill for image processing.

Thanks in advance!

Answer 1

I don’t quite understand what you mean by “quality”, if you mean the quality setting in the JPG compression algorithm, then you can extract it from the EXIF ​​tags of the image (it relies on installing a capture device and no one overwrites them) for see your library here:

http://www.aurigma.com/Support/DocViewer/30/JPEGFileFormat.htm.aspx

If you mean any other “quality," then you need to find a better definition of quality. For example, overexposure can be a problem, in which case looking for saturated pixels will help determine a specific type of quality. Or, more generally, you can see the statistics (mean, standard deviation) of the histogram of the image in three-color channels. The image may not be in focus, and in this case, you can look for a cutoff in the spatial frequencies of the Fourier transform image. If you are worried about speckle noise, you can try applying a median filter to the image and compare it with the original image (a sharper noise will make a bigger change). I have a little guess here.

If by "quality" you mean aesthetic properties of the composition, etc., then - good luck!

Answer 2

The "quality" of an image is not measurable, because it does not correspond to any particular value. If you take this as the number of pixels in an image of a certain size, this is inaccurate. You can talk about a photograph taken in low light conditions as “poor quality,” although it has exactly the same number of pixels as another image taken in good light. This term is often used to discuss the overall effect of an image rather than its technical characteristics.

Answer 3

I wanted to do something similar, but I wanted to use the "Soylent Green" parameter and used people to rank the images by doing comparisons. See the answers to the question .

Answer 4

I think you are asking how to determine the quality of the compression process itself. This can be done by converting JPEG to BMP and comparing BMP with the original bitmap using JPEG. You can iterate over raster images by pixels and calculate the pixel-to-pixel distance by summing the differences between the R, G, and B values ​​of each pair of pixels (that is, the pixel in the original and the pixel in JPEG) and dividing by the total number of pixels. This will give you the average difference between the original and JPEG.

Answer 5

Reading the number of pixels in an image may indicate a “ megapixel ” size (# pixels / 1,000,000), which may be a crude form of software quality check, but it won’t tell you if the photo is correctly focused, assuming it needs to be focused (think about fast moving objects, for example, about trains), not about the weather, or not. looking at this, you will need a person or pigeon if you prefer.