How to NSLog pixel RGB from a UIImage?

Question

I just want to:

1) Copy the pixel data.
2) Iterate and Modify each pixel (just show me how to NSLog the ARGB values as 255)
3) Create a UIImage from the new pixel data

I can figure out the the gory details if someone can just tell me how to NSLog the RGBA values of a pixel as 255. How do I modify the following code to do this? Be Specific Please!

-(UIImage*)modifyPixels:(UIImage*)originalImage
{

NSData* pixelData = (NSData*)CGDataProviderCopyData(CGImageGetDataProvider(originalImage.CGImage));
uint myLength = [pixelData length];

    for(int i = 0; i < myLength; i += 4) {


        //CHANGE PIXELS HERE
        /*
        Sidenote: Just show me how to NSLog them
        */
        //Example:
        //NSLog(@"Alpha 255-Value is: %u", data[i]);
        //NSLog(@"Red 255-Value is: %u", data[i+1]);
        //NSLog(@"Green 255-Value is: %u", data[i+2]);
        //NSLog(@"Blue 255-Value is: %u", data[i+3]);
    }

    //CREATE NEW UIIMAGE (newImage) HERE 

    return newImage;    
}

score 3 · Accepted Answer · answered Aug 30 '09 at 07:48

3

Did this direction work for you? I'd get pixel data like this:

UInt32 *pixels = CGBitmapContextGetData( ctx );

#define getRed(p) ((p) & 0x000000FF)
#define getGreen(p) ((p) & 0x0000FF00) >> 8
#define getBlue(p) ((p) & 0x00FF0000) >> 16
// display RGB values from the 11th pixel
NSLog(@"Red: %d, Green: %d, Blue: %d", getRed(pixels[10]), getGreen(pixels[10]), getBlue(pixels[10]));

answered Aug 30 '09 at 07:48

mahboudz

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4

You're making an assumption about the data format. There's no guarantee that the image is 32bpp ARGB. – Lily Ballard Jan 22 '11 at 03:01

score 1 · Answer 2 · answered Jan 22 '11 at 02:55

If you'd like to actually see the image, you can use Florent Pillet's NSLogger: https://github.com/fpillet/NSLogger

The idea is you start the NSLogger client on your desktop, and then in your app you put this up towards the top:

#import "LoggerClient.h"

And in your modifyPixels method you can do something like this:

LogImageData(@"RexOnRoids",        // Any identifier to go along with the log
             0,                    // Log level
             newImage.size.width,  // Image width
             newImage.size.height, // Image height
             UIImagePNGRepresentation(newImage)); // Image as PNG

Start the client on your desktop, and then run the app on your iphone, and you'll see real images appear in the client. VERY handy for debugging image problems such as flipping, rotating, colors, alpha, etc.

How to NSLog pixel RGB from a UIImage?

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