How do I get the RGB values of an Image? - image-processing

Question

I am taking a computer graphics class, and I need to work with textures, but I can't use any library to do it. I am stuck on loading the rgb values of the images I need to use (the images can be in any format, jpg, raw, png, etc..) so my question is, which is the easiest way to get the rgb values of an image (of any format) without using any libraries to get this values?? Here is what I found already on the site:
unsigned char *data;
File *file;
file = fopen("image.png", "r");//
data = (unsigned char *)malloc(TH*TV*3); //TH and TV are both 50
fread(data, TH*TV*3, 1, file);
fclose(file);
int i;
for(i=0;i<TH*TV*3;i++){
//suposing I have a struct RGB for the rgb values
RGB.r = data[?];// how do I get the r value
RGB.g = data[?];// how do I get the g value
RGB.b = data[?];// how do I get the b value
}
Thanks

Answer 1

Rather than iterating through every byte that you read in, you want to iterate every pixel which consists of 3 bytes. So replace i++ with i+=3.
for(i=0;i<TH*TV*3;i+=3){
RGB.r = data[i];
RGB.g = data[i+1];
RGB.b = data[i+2];
}

Answer 2

Try to use some framework like OpenCV there are several options to get the colors or to manipulate an image.
Here I found this example code:
cv::Mat img = cv::imread("lenna.png");
for(int i=0; i<img.rows; i++) {
for(int j=0; j<img.cols; j++) {
// You can now access the pixel value with cv::Vec3b
std::cout << img.at<cv::Vec3b>(i,j)[0] << " ";
str::cout << img.at<cv::Vec3b>(i,j)[1] << " ";
str::cout << img.at<cv::Vec3b>(i,j)[2] << std::endl;
}
}
But please note that the code above is not very performance, but the code above should give you an idea how to read the pixels.