CODEWITHSUNDEEP
iphoneobjective-crotationuiimage
DixieFlatline
DixieFlatline

Reputation: 8035

UIImage loses quality when rotated

I am using this code to rotate UIImage.

CGFloat DegreesToRads(CGFloat degrees) {
   return degrees * M_PI / 180;
}

- (UIImage *)scaleAndRotateImage:(UIImage *)image forAngle: (double) angle {

    float radians=DegreesToRads(angle);
    // calculate the size of the rotated view's containing box for our drawing space
    UIView *rotatedViewBox = [[UIView alloc] initWithFrame:CGRectMake(0,0, image.size.width, image.size.height)];
    CGAffineTransform t = CGAffineTransformMakeRotation(radians);
    rotatedViewBox.transform = t;
    CGSize rotatedSize = rotatedViewBox.frame.size;

    // Create the bitmap context
    UIGraphicsBeginImageContext(rotatedSize);
    CGContextRef bitmap = UIGraphicsGetCurrentContext();

    // Move the origin to the middle of the image so we will rotate and scale around the center.
    CGContextTranslateCTM(bitmap, rotatedSize.width/2, rotatedSize.height/2);

    //Rotate the image context
    CGContextRotateCTM(bitmap, radians);

    // Now, draw the rotated/scaled image into the context
    CGContextScaleCTM(bitmap, 1.0, -1.0);
    CGContextDrawImage(bitmap, CGRectMake(-image.size.width/2, -image.size.height/2 , image.size.width, image.size.height), image.CGImage );

    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return newImage;

}

Works ok, but the quality of image is worse after rotation. What could be the cause?

Upvotes: 2

Views: 678

Answers (1)

Simone Pistecchia
Simone Pistecchia

Reputation: 2842

try 

UIGraphicsBeginImageContextWithOptions(rotatedSize, NO, 2.0)

from apple documentation:

void UIGraphicsBeginImageContextWithOptions(
   CGSize size,
   BOOL opaque,
   CGFloat scale
);

Parameters

  • size The size (measured in points) of the new bitmap context. This represents the size of the image returned by the UIGraphicsGetImageFromCurrentImageContext function. To get the size of the bitmap in pixels, you must multiply the width and height values by the value in the scale parameter.

  • opaque A Boolean flag indicating whether the bitmap is opaque. If you know the bitmap is fully opaque, specify YES to ignore the alpha channel and optimize the bitmap’s storage. Specifying NO means that the bitmap must include an alpha channel to handle any partially transparent pixels.

  • scale The scale factor to apply to the bitmap. If you specify a value of 0.0, the scale factor is set to the scale factor of the device’s main screen.

bye :)

Upvotes: 6

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