Question

I guess, why I get image distortion on my app, when I use iOS 4.3 on iPad Simulator and device. Look at the screenshot. The same image is displayed normally on iOS 5.1 Simulator and device. Look at the second screenshot… How should I manage this? May be it is possible to write some code before displayed the JPEG?


Unfortunately, I have to repair it, coz my app must work on iOS 4.3 somehow.

This is a method, that is used for the generation of thumbs:

- (UIImage*)imageByScalingAndCroppingForSize:(CGSize)targetSize
{
UIImage *sourceImage = self;
UIImage *newImage = nil;        
CGSize imageSize = sourceImage.size;
CGFloat width = imageSize.width;
CGFloat height = imageSize.height;
CGFloat targetWidth = targetSize.width;
CGFloat targetHeight = targetSize.height;
CGFloat scaleFactor = 0.0;
CGFloat scaledWidth = targetWidth;
CGFloat scaledHeight = targetHeight;
CGPoint thumbnailPoint = CGPointMake(0.0,0.0);

if (CGSizeEqualToSize(imageSize, targetSize) == NO) 
{
    CGFloat widthFactor = targetWidth / width;
    CGFloat heightFactor = targetHeight / height;

    if (widthFactor > heightFactor) 
        scaleFactor = widthFactor; // scale to fit height
    else
        scaleFactor = heightFactor; // scale to fit width
    scaledWidth  = width * scaleFactor;
    scaledHeight = height * scaleFactor;

    // center the image
    if (widthFactor > heightFactor)
    {
        thumbnailPoint.y = (targetHeight - scaledHeight) * 0.5; 
    }
    else 
        if (widthFactor < heightFactor)
        {
            thumbnailPoint.x = (targetWidth - scaledWidth) * 0.5;
        }
}       

UIGraphicsBeginImageContext(targetSize); // this will crop

CGRect thumbnailRect = CGRectZero;
thumbnailRect.origin = thumbnailPoint;
thumbnailRect.size.width  = scaledWidth;
thumbnailRect.size.height = scaledHeight;

[sourceImage drawInRect:thumbnailRect];

newImage = UIGraphicsGetImageFromCurrentImageContext();
if(newImage == nil) 
    NSLog(@"could not scale image");

//pop the context to get back to the default
UIGraphicsEndImageContext();
return newImage;
}

However, if I don’t use this to prepare my image, it is still negative, but works more slow, because images are resized automatically.

This method is used to display image:

-(void) setImage:(UIImage*)image forState:(UIControlState) state
{
[self.buttonView setImage:image forState:state];
}

this way:

[current setImage:thumb forState:UIControlStateNormal];

Yeah, I forgot to mention, that these guys are just custom buttons of a view controller.

Answer 1

I encountered the same problem on 4.3 – turns out that the images were saved with CMYK colors. Switching to RGB and re-saving the images made the problem go away.