C++, how to load images and count pixels of certain colours

here's my problem:

I'm looking for a way to import an image into C++ then traverse its pixels, incrementing a counter every time a pixel of a certain colour is found.

I've done some research, but I haven't found anything particularly useful. DevIL looks like a good option, but I'm not sure where to start.

Here's a bit of C++/python pseudo-code hopefully illustrating what I'm trying to do:

for image in folder:

    A = 0;
    B = 0;

    for pixel in image:

        if (pixel == colourA) {A++}
        if (pixel == colourB) {B++}

    //Output the count of colours for each image
    outputToFile(A, B);

Does anyone have some tips on where to start?

Thanks

EDIT Some extra information: I'm using Windows 7 and all the images are .pngs

EDIT2 I've got everything working, except actually finding out the colour of the current pixel. Currently I'm using this:

int blue = ((uchar *)(img->imageData + pixelX*img->widthStep))[pixelY*img->nChannels + 0];

But it doesn't work, and I have no idea how it works. I haven't been able to find anything about this that I could understand. Could anyone point me in the right direction on how to find the RGB values of a certain pixel?

Edit3 Done! For anyone who finds this trying to do a similar thing, most of my remaining questions a开发者_运维知识库nd a fair bit of code can be found here. Thanks for the help!

You should take a look at OpenCV.

Definiately take a look at OpenCV because when you begin to need more room to move then OpenCV will let you do many more computer vision tasks. And use boost::filesystem to do the 'for each image in dir' code.

Note that the cv::compare function basically does half the work for you already...I'll let you read that and enjoy leveraging the OpenCV API.

Depends on platform and image format. In Windows, BMP images are supported natively (i. e. in the API). ImageMagick is a cross-platform library, pretty universal, takes about any format out there, but it's heavy. Qt has some image processing as well - limited to the most common formats.

SDL has some useful pixel manipulation stuff.

http://www.libsdl.org/

It's very clean as well.