Can any one mail me the code for plotting psnr versus bpp?

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ATHIRA 2014-5-4

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评论： Mohana Singh 2021-1-30

how to plot psnr (peal signal to noise ratio ) versus bpp(bits per pixels)

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Image Analyst 2014-5-4

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Assuming you've varied by bpp and gotten different psnr's for the different bpp

plot(bpp, thePsnr, 'bo-');

bpp and thePsnr are arrays that you've built up by trying different bpp.

Don't use psnr as a variable name because it's the name of a built in function in the Image Processing Toolbox.

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Walter Roberson 2016-6-24

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bpp is not calculated, it is a given (perhaps looped over.)

However, you might be interested in

minpixel = min(YourImage(:));
maxpixel = max(YourImage(:)); 
min_pixel_diff = min( diff( unique(YourImage(:)) ) );
if isempty(min_pixel_diff)
  bits_needed = 1;     %data is a constant
else
  bits_needed = ceil(log2((maxpixel - minpixel) / min_pixel_diff));
end

min_pixel_diff here will become the smallest difference between pixel values that are not identical, and bits_needed becomes the number of bits that you would theoretically need to represent the image in, if you were to scale and shift the image to require the fewest number of bits.

This is not identical to the number of bits actually used in the representation of YourImage. For example, if the image was YourImage = uint16(randi([743, 812], 512, 768, 3)); then it would be represented as 16 bits per image, but you only have a span of at most (812-743+1) which is 70 different values, so you could represent the image as the constant 743 plus a value that needs only 7 bits to distinguish all of the possibilities. The formula here calculates that 7. And the formula works for images represented as values in the range 0 to 1 as well -- for example it could detect that the distinct values are spaced 1/128 apart which again needs 7 bits to represent.

Walter Roberson 2021-1-30

A pixel is a unit with however much memory is required to store all of the color information. In cases of compression or mosaicing then bits per pixel may be non-integer, the mean (average) number required as it is not required that exactly the same amount of memory is used for each pixel.

Mohana Singh 2021-1-30