Sizes for retina when using custom backgrounds for UIButton
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I would like to create a UIButton with a custom background image. It's dimensions need to be 420x88 on retina and 210x44 on standard iPhone screens. (multiplying by 2 for retina) 

When I supply the highres version as the background image, the bottom portion of the image is cut of (I can tell because the image has a border). What size do I need to have my images so the button looks good in high-res and normal otherwise, without the borders getting cutting off?

Here's how I'm creating the button & image:

    UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
    button.frame = CGRectMake(0, 0, 210, 44);
    
    UIEdgeInsets edgeInsets = UIEdgeInsetsMake(0, 16, 0, 16);
    
    // When using 62x88, the bottom portion of the image is cut off
    NSString *imageName = @"button31x44.png";
    
    UIImage *normalImage = [[UIImage imageNamed:imageName] resizableImageWithCapInsets:edgeInsets];    
    [button setBackgroundImage:normalImage forState:UIControlStateNormal];
    button.clipsToBounds = YES;
    button.backgroundColor = [UIColor clearColor];
