Image is rotated after process. How can i do this correctly?

Question

My problem is: UIImage is rotated after processing.

I use a helper class for the image processing called ProcessHelper. This class has two methods:

+ (unsigned char *) convertUIImageToBitmapRGBA8:(UIImage *) image;

+ (UIImage *) convertBitmapRGBA8ToUIImage:(unsigned char *)rawData
                                withWidth:(int) width
                               withHeight:(int) height;

implementation

+ (unsigned char *) convertUIImageToBitmapRGBA8:(UIImage *) image {

    NSLog(@"Convert image [%d x %d] to RGBA8 char data", (int)image.size.width,
                                                       (int)image.size.height);
    CGImageRef imageRef = [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);

    return rawData;
}


+ (UIImage *) convertBitmapRGBA8ToUIImage:(unsigned char *) rawData
                                withWidth:(int) width
                               withHeight:(int) height {

    CGContextRef ctx = CGBitmapContextCreate(rawData,
                                             width,
                                             height,
                                             8,
                                             width * 4,
                                             CGColorSpaceCreateDeviceRGB(),
                                             kCGImageAlphaPremultipliedLast );

    CGImageRef imageRef = CGBitmapContextCreateImage (ctx);
    UIImage* rawImage = [UIImage imageWithCGImage:imageRef];  

    CGContextRelease(ctx);  

    free(rawData);

    return rawImage;
}

I

On start I get pixel data:

    rawData = [ProcessHelper convertUIImageToBitmapRGBA8:image];

Next I do some processing:

-(void)process_grayscale {
int byteIndex = 0;
for (int i = 0 ; i < workingImage.size.width * workingImage.size.height ; ++i)
    {
    int outputColor = (rawData[byteIndex] + rawData[byteIndex+1] + rawData[byteIndex+2]) / 3;

    rawData[byteIndex] = rawData[byteIndex + 1] = rawData[byteIndex + 2] = (char) (outputColor);

    byteIndex += 4;
    }

workingImage = [ProcessHelper convertBitmapRGBA8ToUIImage:rawData
                                                withWidth:CGImageGetWidth(workingImage.CGImage)
                                               withHeight:CGImageGetHeight(workingImage.CGImage)];
}

After this I returned the workingImage to parent class and UIImageView shows it returned but in old size, I mean: image before is WxH and after is WxH but rotated (should be HxW, after rotate). I would like to make the image does not rotate.

This happens when I edit photos from ipad. Screenshots are ok and images from internet like backgrounds are ok.

How can I do this correctly?

Answer 1

use UIGraphicsPushContext(ctx); [image drawInRect:CGRectMake(0, 0, width, height)]; UIGraphicsPopContext(); instead of CGContextDrawImage. CGContextDrawImage will flip the image verticaly.

Or Scale and Transform the Context before calling CGContextDrawImage