Objective C manipulate image - ios

Question

I want to manipulate image and shuffle colors. I'm trying to rotate 180 degress with pixels but failed. I don't want to use UIImageView rotate cause i won't just rotate images. I want to do them whatever i want.
EDIT : It was wrong operator. I dont know why i used % instead of / . Anyways i hope this code helps someone(it works).
- (IBAction)shuffleImage:(id)sender {
[self calculateRGBAsAndChangePixels:self.imageView.image atX:0 andY:0];
}
-(void)calculateRGBAsAndChangePixels:(UIImage*)image atX:(int)x andY:(int)y
{
NSUInteger bytesPerPixel = 4;
NSUInteger bytesPerRow = bytesPerPixel * image.size.width;
NSUInteger bitsPerComponent = 8;
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGContextRef bmContext = CGBitmapContextCreate(NULL, image.size.width, image.size.height, bitsPerComponent,bytesPerRow, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
CGColorSpaceRelease(colorSpace);
CGContextDrawImage(bmContext, (CGRect){.origin.x = 0.0f, .origin.y = 0.0f, image.size.width, image.size.height}, image.CGImage);
UInt8* data = (UInt8*)CGBitmapContextGetData(bmContext);
const size_t bitmapByteCount = bytesPerRow * image.size.height;
NSMutableArray *reds = [[NSMutableArray alloc] init];
NSMutableArray *greens = [[NSMutableArray alloc] init];
NSMutableArray *blues = [[NSMutableArray alloc] init];
for (size_t i = 0; i < bitmapByteCount; i += 4)
{
[reds addObject:[NSNumber numberWithInt:data[i]]];
[greens addObject:[NSNumber numberWithInt:data[i+1]]];
[blues addObject:[NSNumber numberWithInt:data[i+2]]];
}
for (size_t i = 0; i < bitmapByteCount; i += 4)
{
data[i] = [[reds objectAtIndex:reds.count-i%4-1] integerValue];
data[i+1] = [[greens objectAtIndex:greens.count-i%4-1] integerValue];
data[i+2] = [[blues objectAtIndex:blues.count-i%4-1] integerValue];
}
CGImageRef newImage = CGBitmapContextCreateImage(bmContext);
UIImage *imageView = [[UIImage alloc] initWithCGImage:newImage];
self.imageView.image = imageView;
}

Answer 1

Assuming that you are wanting to make the image turn upside down (rotate it 180) and not mirror it, I found some relevant code on another question that may help you:
static inline double radians (double degrees) {return degrees * M_PI/180;}
UIImage* rotate(UIImage* src, UIImageOrientation orientation)
{
UIGraphicsBeginImageContext(src.size);
CGContextRef context = UIGraphicsGetCurrentContext();
if (orientation == UIImageOrientationRight) {
CGContextRotateCTM (context, radians(90));
} else if (orientation == UIImageOrientationLeft) {
CGContextRotateCTM (context, radians(-90));
} else if (orientation == UIImageOrientationDown) {
// NOTHING
} else if (orientation == UIImageOrientationUp) {
CGContextRotateCTM (context, radians(90));
}
[src drawAtPoint:CGPointMake(0, 0)];
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return image;
}
If you're trying to mirror the image, this code example from this question maybe of help:
UIImage* sourceImage = [UIImage imageNamed:#"whatever.png"];
UIImage* flippedImage = [UIImage imageWithCGImage:sourceImage.CGImage
scale:sourceImage.scale
orientation:UIImageOrientationUpMirrored];

Answer 2

So you're looking to actually manipulate the raw pixel data. Check this out then:
Getting the pixel data from a CGImage object
It's for MacOS but should be relevant for iOS as well.