sharpening via weighted discrete cosine transforms

[James L. Dean]

I've written a C command line program to sharpen images.

Around each pixel in the image, this program calculates the fast 2D discrete cosine transform for the shades of the pixels in a rectangle of a specified size around the given pixel, multiplies the AC components of the transform by a specified value, inverts the 2D DCT, and sets the shade of the given pixel to the resulting shade while preserving the hue of the pixel.

Here is an example of an image from my camera and the output from my program:

The program handles the grayscale version of the image similar to the way described by "Discrete Cosine Transform for Enhancing the Contrast of Gray Image" by Nivedita V. Deshmukh (Hippalgaonkar) in the International Journal of Novel Research and Development, Volume 10, Issue 4, April 2025.

Here is an example of an image and the output from my program:

I have attached the C program.

 

[greybeard45 18]

Very interesting. I've done some programming in the past but I am so out of practice it would take me some time to shake the rust off. I do have Visual Studio on my machine and I may try to compile it. Thanks for sharing.

 

[James L. Dean]

There is a good discussion about the algorithm I implemented at sharpening images via weighted discrete cosine transforms. The consensus is it is too slow compared to conventional sharpening algorithms.

 

[Rickbb76 16]

Looks good, "too slow" how slow is it compared to conventional and is it sharper I guess is the bigger question.

 

[James L. Dean]

Very interesting. I've done some programming in the past but I am so out of practice it would take me some time to shake the rust off. I do have Visual Studio on my machine and I may try to compile it. Thanks for sharing.

 

[James L. Dean]

The version of the program attached to this reply takes about three fifths of the time to run (and does the same thing).

 

[James L. Dean]

Does it grossly oversharpen like the original posted version or is it tunable

On the command line, you specify the size of the rectangle to use around each pixel and a multiplier. The multiplier has the biggest effect on sharpening. A value near 1.0 does almost no sharpening. I used 4.0 for the sample image.

 

[James L. Dean]

Attached is a new version of my command line sharpening program (written in C) that applies more sharpening to less sharp pixels.

Also attached is a screen shot of an example of before and after processing.