how can I minimize the total number of bits for an image?
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Iam trying to reduce the number of bits for a 256x256 grayscale image..how does the compression do that using imwrite command or any other method..when I used the imwrite with compression command, the image size still 256x256 and still i have same number of bits.
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Walter Roberson
on 3 Nov 2019
See my recent discussion at https://www.mathworks.com/matlabcentral/answers/488758-how-can-i-reduce-the-bits-per-pixel-in-an-image
Answers (3)
Image Analyst
on 3 Nov 2019
If you look at the size on disk, you will see that it's fewer bytes than you'd expect. imwrite() does the compression internally when you specify a filename with a compressed extension like PNG or JPG. Of course when you call imread(), it will uncompress the image back to it's original size and number of bits in your MATLAB program.
2 Comments
Image Analyst
on 3 Nov 2019
Using imwrite() is one way. It will use it's internal compression methods to make the data in the file have fewer bits. Just try it and see. Compare the file size on disk for extensions .bmp and .jpg and .png and you'll see what I mean.
Tasnim Nazzal
on 4 Nov 2019
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Walter Roberson
on 4 Nov 2019
There are a lot of different techniques available that can reduce the average number of bits written to file per raw input bit. Run length encoding. Huffman encoding. Arithmetic encoding. Zig-Zag encoding with pulse-modulation techniques. LZW compression. And more. Sometimes DCT or wavelet techniques can be made lossless, but those techniques are better suited for lossy encoding.
Tasnim Nazzal
on 4 Nov 2019
2 Comments
Walter Roberson
on 4 Nov 2019
No, that is the wrong thing to do for your purposes. You should follow the hints I gave repeatedly, and do one of Run Length Encoding (look in File Exchange), or Huffman Encoding (see huffmanenc()) or LZW (multiple implementations in File Exchange), or similar, or use a lossy algorithm.
Walter Roberson
on 4 Nov 2019
For this purpose you should be assuming that the destination does not have any file system, so you should not be transmitting bits to be written to a file that is then to be read in.
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