利用drawInRect直接在屏幕上绘制图片

UIImage *iv = [UIImage imageNamed:@"bc.png"];
[iv drawInRect:CGRectMake(0, 0, 100, 100)
     blendMode:kCGBlendModeColorDodge
         alpha:1.0]; // blendMode 设定图片与背景融合方式