Despeckle

[el_supremo]

I had assumed that MagickDespeckleImage would remove "pepper" from an image but that doesn't appear to be the case (I'm using IM 6.4.4-5). What does it actually do?
The code below creates a white 800x600 image, peppers it with random black spots and then despeckles it, saving before and after images. The before image has pure black spots on a pure white background. The despeckle operation changes all black spots (0) to slightly lighter ones (16) and also adds a light gray border around them and around the entire image.
If this is what's supposed to happen, which operation should I be using to remove the "pepper" from the image?

Thanks
Pete

Code: Select all

#include <windows.h>
#include <wand/magick_wand.h>

void test_wand(LPTSTR lpCmdLine)
{
	MagickWand *mw = NULL;
	unsigned char image[800*600],*ip;
	int i,j,k;

	MagickWandGenesis();
	mw  = NewMagickWand();
	ip = image;
	for(i=0;i<600;i++) {
		for(j=0;j<800;j++) {
		*ip++ = 255;
		}
	}
	srand(time(0));
	for(i=0;i<500;i++) {
		// plonk some random black pixels in the image
		j = rand()%600;
		k = rand()%800;
		image[k*j] = 0;
	}
	MagickConstituteImage(mw,800,600,"I",CharPixel,image);
	MagickWriteImage(mw,"pepper.png");
	MagickDespeckleImage(mw);
	MagickWriteImage(mw,"pepper_despeckle.png");
	DestroyMagickWand(mw);
    MagickWandTerminus();
}

[fmw42]

I had assumed that MagickDespeckleImage would remove "pepper" from an image but that doesn't appear to be the case (I'm using IM 6.4.4-5). What does it actually do?
The code below creates a white 800x600 image, peppers it with random black spots and then despeckles it, saving before and after images. The before image has pure black spots on a pure white background. The despeckle operation changes all black spots (0) to slightly lighter ones (16) and also adds a light gray border around them and around the entire image.
If this is what's supposed to happen, which operation should I be using to remove the "pepper" from the image?

Thanks
Pete

Pete,

As I don't use your API, only the command line, I cannot generate your example. Can you post an example of your resulting image? How isolated is the noise?

Have you tried just using -median?

You might also want to look at my scripts, isonoise and statsfilt, and perhaps try to convert them to your API code, if they work well on your image.

Fred

[el_supremo]

Have you tried just using -median?

Thanks, Fred. That works a lot better. I'm also trying out the technique in your isofilter which may be the best option since it has a greater effect on the "pepper" than anything else in the image which is what I was looking for.

Pete