Question

I have array with colors as its objects. I want to create an image out of it.
Actually, what is happening is , i’m taking the pixel value of each pixel of an image, modify it and store in a mutable array its object. Now want to draw an image from this. How to do that?? ANy idea???

-(UIImage*)modifyPixels:(UIImage*)originalImage {
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc]init];
    NSMutableArray *result =[[NSMutableArray alloc]init];
    int width = img.size.width;
    int height = img.size.height;
        originalImage = imageView.image;

    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

    unsigned char *rawData = malloc (height * width * 4);
    NSUInteger bytesPerPixel = 4;
    NSUInteger bytesPerRow = bytesPerPixel * width;
    NSUInteger bitsPerComponent = 8;
    CGContextRef context = CGBitmapContextCreate(rawData, width, height, bitsPerComponent, bytesPerRow, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
    CGColorSpaceRelease(colorSpace);

    CGContextDrawImage(context, CGRectMake(0, 0, width, height),img.CGImage);
    CGContextRelease(context);
    int byteIndex = 0;
    for (int xx=0;xx<width;xx++){
        for (int yy=0;yy<height;yy++){
    // Now rawData contains the image data in the RGBA8888 pixel format.
            NSLog(@"(%d,%d)",xx,yy);
    NSLog(@"Alpha 255-Value is: %u", rawData[byteIndex + 3]);
    NSLog(@"Red 255-Value is: %u", rawData[byteIndex]);
    NSLog(@"Green 255-Value is: %u",rawData[byteIndex + 1]);
    NSLog(@"Blue 255-Value is: %u",rawData[byteIndex + 2]);
            CGFloat red   = (rawData[byteIndex]+rawData[byteIndex + 1]+rawData[byteIndex + 2]) / 3;
            CGFloat green = red;
            CGFloat blue  = red;
            CGFloat alpha = 255;
            byteIndex += 4;

            UIColor *acolor = [UIColor colorWithRed:red green:green blue:blue alpha:alpha];
            [result addObject:acolor];
                }

        }
        UIImage *newImage;  
        //CREATE NEW UIIMAGE (newImage) HERE from acolor(array of colors)
//this is the portion i'm in trouble with

        return newImage;    
        [pool release];
    }

Answer 1

As far as I understand you try average all channels.
You could try the following approach which uses Core Graphics:

CGImageRef inImage = mainImageView.image.CGImage;          
CFDataRef dataRef = CGDataProviderCopyData(CGImageGetDataProvider(inImage));  
UInt8* pixelBuffer = (UInt8*)CFDataGetBytePtr(dataRef);  
int length = CFDataGetLength(dataRef);  
for (int index = 0; index < length; index += 4)  
{  
    pixelBuffer[index + 1] = (pixelBuffer[index + 1] + pixelBuffer[index + 2] + pixelBuffer[index + 3])/3.0;  
    pixelBuffer[index + 2] = pixelBuffer[index + 1];  
    pixelBuffer[index + 3] = pixelBuffer[index + 1];      
}  
CGContextRef ctx = CGBitmapContextCreate(pixelBuffer,  
                                         CGImageGetWidth( inImage ),  
                                         CGImageGetHeight( inImage ),  
                                         8,  
                                         CGImageGetBytesPerRow( inImage ),  
                                         CGImageGetColorSpace( inImage ),  
                                         kCGImageAlphaPremultipliedFirst );  
CGImageRef imageRef = CGBitmapContextCreateImage(ctx);  
UIImage* rawImage = [UIImage imageWithCGImage:imageRef];  
CGContextRelease(ctx);  
CFRelease(dataRef);
CGImageRelease(imageRef);

The result is stored in rawImage.

You could also take a look at the GLImageProcessing sample from Apple.
This shows some basic image processing techniques on the iPhone using OpenGL.