IOS High Quality Screenshot

Question

I take a screenshot of my iPad 3 like this:

UIGraphicsBeginImageContext(self.view.frame.size);
[self.view.layer renderInContext:UIGraphicsGetCurrentContext()];
UIImage *viewImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,
                                                     NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];

int num = arc4random() % 100000000000000;

NSString* path = [documentsDirectory stringByAppendingPathComponent: [NSString stringWithFormat:@"%dtest.png", num]];
NSData* data = UIImagePNGRepresentation(viewImage);
[data writeToFile:path atomically:YES];

The problem is that I have a big loss in quality. I can see the pixels, but this is an iPad 3, so how can it be?

Answer 1

- (UIImage*)screenshot 
{
    // Create a graphics context with the target size
    // On iOS 4 and later, use UIGraphicsBeginImageContextWithOptions to take the scale into consideration
    // On iOS prior to 4, fall back to use UIGraphicsBeginImageContext
    CGSize imageSize = [[UIScreen mainScreen] bounds].size;
    if (NULL != UIGraphicsBeginImageContextWithOptions)
        UIGraphicsBeginImageContextWithOptions(imageSize, NO, 0);
    else
        UIGraphicsBeginImageContext(imageSize);

    CGContextRef context = UIGraphicsGetCurrentContext();

    // Iterate over every window from back to front
    for (UIWindow *window in [[UIApplication sharedApplication] windows]) 
    {
        if (![window respondsToSelector:@selector(screen)] || [window screen] == [UIScreen mainScreen])
        {
            // -renderInContext: renders in the coordinate space of the layer,
            // so we must first apply the layer geometry to the graphics context
            CGContextSaveGState(context);
            // Center the context around the window anchor point
            CGContextTranslateCTM(context, [window center].x, [window center].y);
            // Apply the window transform about the anchor point
            CGContextConcatCTM(context, [window transform]);
            // Offset by the portion of the bounds left of and above the anchor point
            CGContextTranslateCTM(context,
                                  -[window bounds].size.width * [[window layer] anchorPoint].x,
                                  -[window bounds].size.height * [[window layer] anchorPoint].y);

            // Render the layer hierarchy to the current context
            [[window layer] renderInContext:context];

            // Restore the context
            CGContextRestoreGState(context);
        }
    }

    // Retrieve the screenshot image
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();

    return image;
}

more information read this technical report: Technical Q & A QA1703 Screen capture in UIKit applications

Answer 2

From the doc:

UIGraphicsBeginImageContextWithOptions
Creates a bitmap-based graphics context with the specified options.

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

Then:

UIGraphicsBeginImageContextWithOptions(self.view.frame.size,NO,2.0);

Answer 3

Your size is wrong, use this:

CGRect screenBounds = [[UIScreen mainScreen] bounds];
CGFloat screenScale = [[UIScreen mainScreen] scale];
CGSize screenSize = CGSizeMake(screenBounds.size.width * screenScale, screenBounds.size.height * screenScale);
UIGraphicsBeginImageContext(screenSize);
//screenshot code..