Q: I'm looking to use the iPhone camera to take a photo and then replace the green screen in that photo with another photo.
What's the best way to dive into this? I couldn't find many resources online.
Thanks in advance!
Conceptually, all that you need to do is loop through the pixel data of the photo taken by the phone, and for each pixel that is not within a certain range of green, copy the pixel into the same location on your background image.
Here is an example I modified from keremic's answer to another stackoverflow question. NOTE: This is untested and just intended to give you an idea of a technique that will work
//Get data into C array
CGImageRef image = [UIImage CGImage];
NSUInteger width = CGImageGetWidth(image);
NSUInteger height = CGImageGetHeight(image);
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
NSUInteger bytesPerPixel = 4;
NSUInteger bytesPerRow = bytesPerPixel_ * width;
NSUInteger bitsPerComponent = 8;
unsigned char *data = malloc(height * width * bytesPerPixel);
// you will need to copy your background image into resulting_image_data.
// which I am not showing here
unsigned char *resulting_image_data = malloc(height * width * bytesPerPixel);
CGContextRef context = CGBitmapContextCreate(rawData, width, height, bitsPerComponent, bytesPerRow, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
CGColorSpaceRelease(colorSpace);
CGContextDrawImage(context, CGRectMake(0, 0, width, height));
CGContextRelease(context);
//loop through each pixel
for(int row = 0; row < height; row++){
for(int col = 0; col < width*bytesPerPixel; col=col+4){
red = data[col];
green = data[col + 1];
blue = data[col + 2];
alpha = data[col + 3];
// if the pixel is within a shade of green
if(!(green > 250 && red < 10 && blue < 10)){
//copy them over to the background image
resulting_image_data[row*col] = red;
resulting_image_data[row*col+1] = green;
resulting_image_data[row*col+2] = blue;
resulting_image_data[row*col+3] = alpha;
}
}
}
//covert resulting_image_data into a UIImage