Noise and Blur in Cuda

Question

I'm trying to add noise and blur functions to my project in Cuda and after quite some research i've hit a bit of a stumbling block, I've read up on the Gaussian blur matrix but i'm still having trouble getting a working piece of code which would be able to blur certain parts of an image, I've managed to get a form of noise to show. If anyone could give a bit of help in either explaining how to implement a Gaussian or a simpler blur method or even providing a bit of code which implements blurring. Gratefully appreciated!!

Answer 1

Gaussian blur is a separable filter, so you can apply the 1D kernel first to all the rows in your ROI and then to the columns of the blurred rows.

The tricky part with CUDA is that this is a neighbourhood operation, so typically you will need to have each block overlap by half the kernel size in order to get the required neighbourhood pixels into shared memory.

Answer 2

FYI, these are two separate questions and should be asked separately in this site.

Regarding the blur - for large blur kernels (strong blurs) the best approach is to use the FFT on the image and on a Gaussian noise kernel image then multiply the results using the complex multiplication and inverse FFT that result. You will have to implement a FFT-Shift function yourself and if you are using color images, you will have to split the image into a separate buffer per channel.

For small blur kernels (gentile blurs) the simplest approach is for each pixel in the result image, sum nearby pixels in the source image (with a Gaussian weight function).

Regarding the noise - test easiest approach is to load a pre-generated pseudo-random generator's result image into CUDA after transforming it from uniformly distributed random numbers to normal distributed random numbers. E.g. this question.

The a correctly size region in the random image should be multiplied by the noise sigma and added to the source image to receive the result.

Last time I checked there was no random buffer generation solution for CUDA, however, that was a few years ago.

Update: CUDA now has cuRand so you should be able to generator random numbers instead of using a pregenerated random buffer.