ios - 裁剪后的 iOS 图像返回太大

Question

一整天都在尝试解决这个问题，但没有成功。

差不多，我正在截取 View 的屏幕截图，然后尝试裁剪掉前 50 像素和页脚。问题是，当我这样做时，结果有点夸张，并且质量下降。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;
}

Answer 1

我发现裁剪非常困惑!

我不确定你到底想做什么，但这可能就是......

-(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;
    }

也考虑这个有值(value)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，如果您使用相机，请不要忘记这一点“宇宙中最有用的代码!” iOS UIImagePickerController result image orientation after upload

希望能有所帮助