For those who are wondering, the additional code looks like this. I didn’t accomodate image offset since my image takes up the entire view. YMMV. My image was smaller than my frame. You might have to flip the division if your ratio is the opposite.

size_t w = CGImageGetWidth(inImage); //Written by Mark
size_t h = CGImageGetHeight(inImage); //Written by Mark
float xscale = w / self.frame.size.width;
float yscale = h / self.frame.size.height;
point.x = point.x * xscale;
point.y = point.y * yscale;

Looks great. I also found another color picker at http://www.v-vent.com/blog/?p=27 which might be able to be combined to have a pointer on the screen to show what pixel is being examined in the image.

A comment on scaling for those who have asked about it. You should be able to take the x,y of the current touch, subtract any offset to match the image frame, then scale the x,y point by the inverse scaling factor from the image in memory to the screen image, which should point to the correct pixel in the original unscaled image.

It only becomes a problem if you allow the user to modify the scaling factor by pinching the image, which then means you have to do a little more work to find out what part of the image is being displayed, and how it fits into the original image.

Great post! And thanks, Mark, for the re-usable class.

it was a nice article, mark can we also set the color of the pixel ?? i m trying to do that but still not able to find out the way in Quartz2d. your help would highly be appriciated.

Regards,
Usman

CGContextRelease(cgctx);
Incorrect decrement of the reference count of an object is not owned at this point by the caller

and

return context;
Potential leak of an object allocated on line 116 and stored into ‘context’

Quite frankly, I haven’t messed around with much CoreGraphics stuff, and this is gibberish to me, but I thought I’d let you know.

Again, I appreciate you sharing this bit of code with us. Thanks!

Thanks! Code is great, like the port from the Apple sample code. Very cool stuff.

colorSpace = CGColorSpaceCreateWithName(kCGColorSpaceGenericRGB);

by this one

colorSpace = CGColorSpaceCreateDeviceRGB();

thanks master is a great contribution.