裁剪的 iOS 图像返回太大答案

【问题标题】：Cropped iOS Image comes back too large裁剪的 iOS 图像返回太大
【发布时间】：2014-07-06 04:01:53
【问题描述】：

整天都在尝试解决这个问题，但无济于事。

差不多，我正在截取视图的屏幕截图，然后尝试裁剪前 50 像素和页脚。问题是，当我这样做时，结果有点夸张，质量下降。这是我写的，我认为符合视网膜。

-(UIImage *)takeSnapShotAndReturn{
      //Take screenshot of whole view
    if([[UIScreen mainScreen] respondsToSelector:@selector(scale)]){
        UIGraphicsBeginImageContextWithOptions(self.view.bounds.size,NO,[UIScreen  mainScreen].scale);
    }
    else{
        UIGraphicsBeginImageContext(self.view.window.bounds.size);
    }
    [self.view.layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    combinedImage = [self cropOutArea:image withRectangle:CGRectMake(0, 50, 320, 467)];
    UIImageWriteToSavedPhotosAlbum(combinedImage, nil, nil, nil);
    UIGraphicsEndImageContext();

    return image;
}

-(UIImage *)cropOutArea:(UIImage*)image withRectangle:(CGRect)rectangle{
    if(image.scale > 1){
        rectangle = CGRectMake(rectangle.origin.x    * image.scale,
                               rectangle.origin.y    * image.scale,
                               rectangle.size.width  * image.scale,
                               rectangle.size.height * image.scale);
    }

    CGImageRef imageRef = CGImageCreateWithImageInRect(image.CGImage, rectangle);
    UIImage *result = [UIImage imageWithCGImage:imageRef scale:image.scale orientation:image.imageOrientation];
    CGImageRelease(imageRef);

    return result;
}

【问题讨论】：

标签： ios crop retina

【解决方案1】：

在cropOutArea 中释放result 之前尝试设置此BOOL 属性。

result.layer.masksToBounds = YES

【讨论】：

它说在 UIImage 的对象类型上找不到“层” *
对不起，UIImageView 有“层”，所以你必须先UIImageView *resultView = [[UIImageView alloc] initWithImage:result]。那么你可以resultView.layer.masksToBounds = YES。这意味着您将发布UIImageView 而不是UIImage，因此您必须更改cropOutArea 的返回值。
好的。试过了，4寸屏幕还是放大了。不过 3.5 英寸也可以。

【解决方案2】：

我发现裁剪非常令人困惑！

我不确定你到底想做什么，但这可能是它.....

-(UIImage *)simplishTopCropAndTo640:(UIImage *)fromImage
        // moderately optimised!
    {
    float shortDimension = fminf(fromImage.size.width, fromImage.size.height);

    // 1.use CGImageCreateWithImageInRect to take only the top square...
    // 2. use drawInRect (or CGContextDrawImage, same) to scale...

    CGRect topSquareOfOriginalRect =
      CGRectMake(0,0, shortDimension,shortDimension);
                // NOT fromImage.size.width,fromImage.size.width);

    CGImageRef topSquareIR = CGImageCreateWithImageInRect(
                fromImage.CGImage, topSquareOfOriginalRect);

    CGSize size = CGSizeMake( 640,640 );
    CGRect sized = CGRectMake(0.0f, 0.0f, size.width, size.height);

    UIGraphicsBeginImageContextWithOptions(size, NO, 0.0f);
    CGContextRef cc = UIGraphicsGetCurrentContext();
    CGContextSetInterpolationQuality(cc, kCGInterpolationLow);

    CGContextTranslateCTM(cc, 0, size.height);
    CGContextScaleCTM(cc, 1.0, -1.0);
    CGContextDrawImage(cc, sized, topSquareIR );
    // arguably, those three lines more simply...
    //[[UIImage imageWithCGImage:topSquareIR] drawInRect:sized];
    CGImageRelease(topSquareIR);

    UIImage *result = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    result =
    [UIImage imageWithCGImage:result.CGImage
              scale:result.scale
              orientation: fromImage.imageOrientation];

    //consider...something like...
    //[UIImage imageWithCGImage:cgimg
    //       scale:3 orientation:fromImage.imageOrientation];

    return result;
    }

考虑一下这个有价值的类别.....

-(UIImage *)ordinaryCrop:(CGRect)toRect
    {
    // crops any image, to any rect.  you can't beat that

    CGImageRef imageRef = CGImageCreateWithImageInRect([self CGImage], toRect);
    UIImage *cropped = [UIImage imageWithCGImage:imageRef];
    CGImageRelease(imageRef);
    return cropped;
    }

最后，如果您使用的是“宇宙中最有用的代码”，请不要忘记这一点！ iOS UIImagePickerController result image orientation after upload

希望对你有所帮助

【讨论】：