How to get the Raw pixel data from CGImage

Question

How to get the Pixel Data of UIimage after scaling and moving,I wan to get the CGImage Pixel Data and then get the UIImage from CGImage Pixel Data.How can we do this?.

Answer 1

You can get the rawdata by calling

CFDataRef rawData = CGDataProviderCopyData(CGImageGetDataProvider(aCGImageRef));

You can step through pixels like this:

UInt8 * buf = (UInt8 *) CFDataGetBytePtr(rawData); 
CFIndex length = CFDataGetLength(rawData);

for(unsigned long i=0; i<length; i+=4)
{
    int r = buf[i];
    int g = buf[i+1];
    int b = buf[i+2];
     }
CFRelease(rawData);

Answer 2

Try this. This will give you Offset, Alpha, RGB Color etc of selected pixel of an image.

Source Code:-

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event 
{
UITouch *touch = [[event allTouches] anyObject]; 

CGPoint startLocation   = [touch locationInView:self.view];

    if ([touch view] == YourImageView)
    {
        CGPoint location = [touch YourImageView];
        [self getPixelColorAtLocation:location];
        if((alpha==255)||(alpha==0))
        {
            //perform Your task
        }
    }
} 


- (UIColor*) getPixelColorAtLocation:(CGPoint)point 
{

UIColor* color = nil;

CGImageRef inImage;

inImage = YourImageView.image.CGImage;


// Create off screen bitmap context to draw the image into. Format ARGB is 4 bytes for each pixel: Alpa, Red, Green, Blue
CGContextRef cgctx = [self createARGBBitmapContextFromImage:inImage];
if (cgctx == NULL) { return nil; /* error */ }

size_t w = CGImageGetWidth(inImage);
size_t h = CGImageGetHeight(inImage);
CGRect rect = {{0,0},{w,h}};


// Draw the image to the bitmap context. Once we draw, the memory 
// allocated for the context for rendering will then contain the 
// raw image data in the specified color space.
CGContextDrawImage(cgctx, rect, inImage); 

// Now we can get a pointer to the image data associated with the bitmap
// context.
unsigned char* data = CGBitmapContextGetData (cgctx);
if (data != NULL) {
    //offset locates the pixel in the data from x,y. 
    //4 for 4 bytes of data per pixel, w is width of one row of data.
    int offset = 4*((w*round(point.y))+round(point.x));
    alpha =  data[offset]; 
    int red = data[offset+1]; 
    int green = data[offset+2]; 
    int blue = data[offset+3]; 
    NSLog(@"offset: %i colors: RGB A %i %i %i  %i",offset,red,green,blue,alpha);
    color = [UIColor colorWithRed:(red/255.0f) green:(green/255.0f) blue:(blue/255.0f) alpha:(alpha/255.0f)];
}

// When finished, release the context
//CGContextRelease(cgctx); 
// Free image data memory for the context
if (data) { free(data); }

return color;
}

- (CGContextRef) createARGBBitmapContextFromImage:(CGImageRef)inImage 
{
CGContextRef    context = NULL;
CGColorSpaceRef colorSpace;
void *          bitmapData;
int             bitmapByteCount;
int             bitmapBytesPerRow;

// Get image width, height. We'll use the entire image.
size_t pixelsWide = CGImageGetWidth(inImage);
size_t pixelsHigh = CGImageGetHeight(inImage);

// Declare the number of bytes per row. Each pixel in the bitmap in this
// example is represented by 4 bytes; 8 bits each of red, green, blue, and
// alpha.
bitmapBytesPerRow   = (pixelsWide * 4);
bitmapByteCount     = (bitmapBytesPerRow * pixelsHigh);

// Use the generic RGB color space.
colorSpace = CGColorSpaceCreateDeviceRGB();

if (colorSpace == NULL)
{
    fprintf(stderr, "Error allocating color space\n");
    return NULL;
}

// Allocate memory for image data. This is the destination in memory
// where any drawing to the bitmap context will be rendered.
bitmapData = malloc( bitmapByteCount );
if (bitmapData == NULL) 
{
    fprintf (stderr, "Memory not allocated!");
    CGColorSpaceRelease( colorSpace );
    return NULL;
}

// Create the bitmap context. We want pre-multiplied ARGB, 8-bits 
// per component. Regardless of what the source image format is 
// (CMYK, Grayscale, and so on) it will be converted over to the format
// specified here by CGBitmapContextCreate.
context = CGBitmapContextCreate (bitmapData,
                                 pixelsWide,
                                 pixelsHigh,
                                 8,      // bits per component
                                 bitmapBytesPerRow,
                                 colorSpace,
                                 kCGImageAlphaPremultipliedFirst);
if (context == NULL)
{
    free (bitmapData);
    fprintf (stderr, "Context not created!");
}

// Make sure and release colorspace before returning
CGColorSpaceRelease( colorSpace );

return context;
}

Hope it helps. Thanks :)