iOS UIImage节省质量损失？

Question

I seem to be losing quality when saving an UIImage to the Photo Library. Any ideas how to fix it? Here is the important code:

-(IBAction)aExportPhoto:(id)sender
{
UIImage *main = [self imageWithView:imageFrame];
UIImage *water = [self imageWithView:waterFrame];
UIImage *lign = [self imageWithView:lignFrame];

CGRect fMain = imageFrame.frame;
CGRect fWater = waterFrame.frame;
CGRect fLign = lignFrame.frame;

CGSize sMain = fMain.size;
CGSize sWater = fWater.size;
CGSize sLign = fLign.size;

UIGraphicsBeginImageContext(sMain);

[main drawInRect:CGRectMake(0, 0, sMain.width, sMain.height)];
[lign drawInRect:CGRectMake(fMain.origin.x, sMain.height - 25, sMain.width - 45, 20) blendMode:kCGBlendModeNormal alpha:1.0f];
[water drawInRect:CGRectMake(sMain.width - 45, sMain.height - 35, 40, 40) blendMode: kCGBlendModeNormal alpha: 1.0f];

UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
UIImageWriteToSavedPhotosAlbum(newImage, nil, nil, nil);
UIGraphicsEndImageContext();

}

Here is the imageWithView method:

- (UIImage *) imageWithView:(UIImageView *)view
{
UIGraphicsBeginImageContextWithOptions(view.bounds.size, view.opaque, 0.0);
[view.layer renderInContext:UIGraphicsGetCurrentContext()];

UIImage * img = UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();

return img;
}

Thanks in advance!

Answer 1

You should use UIGraphicsBeginImageContextWithOptions in aExportPhoto , like you did in imageWithView . UIGraphicsBeginImageContext uses a scale of 1 (non-retina resolution), and you want to use 0 (the scale of the device).