iOS Screen Capture is blurry

问题

I am having trouble getting a screen shot that is not blurry - first I tried this:

Screen capture for iOS

and it was not blurry but I think Apple will not let this code through - won't make the review?

so I went with the official solution in the developer docs: similar to this: Capturing Screen

But when I use the 'official' way, the image it creates is blurry

Here is the code I am using straight from the dev support docs (iOS6 and I am scaling it, but there is no difference if scale is 0):

CGSize imageSize = [[UIScreen mainScreen] bounds].size;

if (NULL != UIGraphicsBeginImageContextWithOptions)
    UIGraphicsBeginImageContextWithOptions(imageSize, NO, 0.65);
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's geometry to the graphics context
        CGContextSaveGState(context);
        // Center the context around the window's anchor point
        CGContextTranslateCTM(context, [window center].x, [window center].y);
        // Apply the window's 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;

回答1:

UIGraphicsBeginImageContextWithOptions(CGSize size, BOOL opaque, CGFloat scale) allows you to create graphic bitmap context which supports high resolution screens by applying scale factor.

If you specify a value of 0.0 then the scale factor is set to the scale factor of the device’s main screen. On a standard-resolution screen, the scale factor is typically 1.0. On a high-resolution screen, the scale factor is typically 2.0.

In your case you specify the value of 0.65

UIGraphicsBeginImageContextWithOptions(imageSize, NO, 0.65);

So some blurring effect occurs

You can get complete information about using scale factor in iOS Drawing Concepts Guide Points Versus Pixels

来源：https://stackoverflow.com/questions/16849944/ios-screen-capture-is-blurry

标签

ios

screen

image-capture