How to access the elements of single channel IplImage in Opencv

Question

How can I access the Elements of an IplImage (single channel and IPL_DEPTH_8U depth).

I want to change the pixel value at a particu

Answer 1

The fast way to get the pixel value is use macro.

CV_IMAGE_ELEM( image_header, elemtype, y, x_Nc ) 

And in your case, the Image is single channel.So you can get the i,j pixel value by

CV_IMAGE_ELEM(image, unsigned char, i, j)

Answer 2

opencv provide CV_IMAGE_ELEM method to access elements of IplImage,it's a macro,

define CV_IMAGE_ELEM( image, elemtype, row, col )       \
    (((elemtype*)((image)->imageData + (image)->widthStep*(row)))[(col)])

second parameter is the type of

Answer 3

Pixels are stored inside imageData array. So, since your image is single channel you just have to do like:

myimage.imageData[y*myimage.width+x] = 100;

This ensure in imageData the right offset from beginning of buffer, and it's more readable than any other pointer algebra operation.

In N-channels images it's enough to multiply by N the array offset, and add the number of channel to read:

i.e. for an RGB image

myimage.imageData[3*(y*myimage.width+x)+0] = 100; //Red
myimage.imageData[3*(y*myimage.width+x)+1] = 100; //Green
myimage.imageData[3*(y*myimage.width+x)+2] = 100; //Blue

Any optimization to avoid to multiply data to obtain index can be done according to the goal you have to achieve.