UIImage resize and crop to fit frame - objective-c

Question

I know this question has been asked several times, but their answers make my images loose quality. They all become pixelated. So even though it crops and resizes correctly it looses quality.
Just so you can check it, this is the algorithm which is in every post:
- (UIImage*)scaleAndCropImage:(UIImage *)aImage forSize:(CGSize)targetSize
{
UIImage *sourceImage = aImage;
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;
}

Answer 1

On the line where your begin the UIGraphicsImageContext, use UIGraphicsBeginImageContextWithOptions instead of UIGraphicsBeginImageContext. Try something like this:
UIGraphicsBeginImageContextWithOptions(targetSize, NO, 0.0)
Notice the three parameters passed above, I'll go through them in order:
targetSize is the size of the image measured in points (not pixels)
NO is a BOOL value (could be YES or NO) that indicates whether the image is 100% opaque or not. Setting this to NO will preserve transparency and create an alpha channel to handle transparency.
The most important part of the above code is the final parameter, 0.0. This is the image scale factor that will be applied. Specifying the value to 0.0 sets the scale factor of the current device's screen. This means that the quality will be preserved, and look especially good on Retina Displays.
Here's the Apple Documentation on UIGraphicsBeginImageContextWithOptions.

Answer 2

You should use UIGraphicsBeginImageContextWithOptions(targetSize, false, 0.0) instead of UIGraphicsBeginImageContext(targetSize) so the correct scale factor gets applied to the bitmap.
Specifying 0.0 as scale factor, sets the scale factor to that from the device's main screen.
Calling only UIGraphicsBeginImageContext() is the same as calling
UIGraphicsBeginImageContextWithOptions(..) with a scale factor of 1.0
for more details take a look at: http://developer.apple.com/library/ios/documentation/UIKit/Reference/UIKitFunctionReference/Reference/reference.html#//apple_ref/c/func/UIGraphicsBeginImageContextWithOptions