Negative value color apply into Image - ios

Question

I want to apply negative value of RGB into image.
R: -8
G: -89
B: -76
I know that the value of RGB is in between 0 to 255 but i want to apply minus value and set offset something like that but don't know how to do.
I am using following link for reference.
http://blog.swishzone.com/?p=9606
I am using
red value = (original red value * redMultiplier) + redOffset
green value = (original green value * greenMultiplier) + greenOffset
blue value = (original blue value * blueMultiplier) + blueOffset
But it not working as i want.

Answer 1

Found one solution for change image color using negative RGB values. Following is the method without affecting alpha of image.
-(void)ColorChangeProcessing :(int )redvalue greenValue:(int)greenvalue blueValue:(int)bluevalue imageUsed : (UIImageView *)image
{
CGContextRef ctx;
CGImageRef imageRef = [image.image CGImage];
NSUInteger width = CGImageGetWidth(imageRef);
NSUInteger height = CGImageGetHeight(imageRef);
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), imageRef);
CGContextRelease(context);
int byteIndex = (bytesPerRow * 0) + 0 * bytesPerPixel,RED = redvalue,GREEN=greenvalue,BLUE = bluevalue;
for (int ii = 0 ; ii < width * height ; ++ii)
{
if( rawData[byteIndex+3] != 0 && (rawData[byteIndex] != '/0' || rawData[byteIndex+1] != '/0' || rawData[byteIndex+2] != '/0' ))
{
if ((((rawData[byteIndex])+RED)) > 255)
{
rawData[byteIndex] = (char)255;
}
else if((((rawData[byteIndex])+RED)) >0)
{
rawData[byteIndex] = (char) (((rawData[byteIndex] * 1.0) + RED));
}
else
{
rawData[byteIndex] = (char)0;
}
if ((((rawData[byteIndex+1])+GREEN)) > 255)
{
rawData[byteIndex+1] = (char)255;
}
else if((((rawData[byteIndex+1])+GREEN))>0)
{
rawData[byteIndex+1] = (char) (((rawData[byteIndex+1] * 1.0) + GREEN));
}
else
{
rawData[byteIndex+1] = (char)0;
}
if ((((rawData[byteIndex+2])+BLUE)) > 255)
{
rawData[byteIndex+2] = (char)255;
}
else if((((rawData[byteIndex+2])+BLUE))>0)
{
rawData[byteIndex+2] = (char) (((rawData[byteIndex+2] * 1.0) + BLUE));
}
else
{
rawData[byteIndex+2] = (char)0;
}
}
byteIndex += 4;
}
ctx = CGBitmapContextCreate(rawData,
CGImageGetWidth( imageRef ),
CGImageGetHeight( imageRef ),
8,
CGImageGetBytesPerRow( imageRef ),
CGImageGetColorSpace( imageRef ),
kCGImageAlphaPremultipliedLast );
CGImageRef NewimageRef = CGBitmapContextCreateImage (ctx);
UIImage* rawImage = [UIImage imageWithCGImage:NewimageRef];
tempViewForProcessingColors = [[UIImageView alloc] init];
tempViewForProcessingColors = [[arrayWithDictionary objectAtIndex:ImageCount]valueForKey:#"imageView"];
// NSLog(#"Name: %# --- Red: %d --- Green: %d --- Blue: %d",tempViewForProcessingColors.accessibilityLabel,RED,GREEN,BLUE);
tempViewForProcessingColors.image = rawImage;
//ImageCount++;
CGContextRelease(ctx);
free(rawData);
CGImageRelease(NewimageRef);
}