应用 CIFIlter 后设置 UIImageView 内容模式

Question

感谢收看。

这是我的代码

 CIImage *result = _vignette.outputImage;
self.mainImageView.image = nil;
//self.mainImageView.contentMode = UIViewContentModeScaleAspectFit;
self.mainImageView.image = [UIImage imageWithCIImage:result];
self.mainImageView.contentMode = UIViewContentModeScaleAspectFit;

在这里_vignette 正确设置了滤镜，并且图像效果正确应用于图像。

我正在使用分辨率为 500x375 的源图像。我的 imageView 几乎具有 iPhone 屏幕的分辨率。所以为了避免拉伸，我使用了 AspectFit。

但是当我将结果图像分配回我的 imageView 时应用效果后，它会拉伸。无论我使用哪个UIViewContentMode。它不起作用。无论我给出什么过滤器，它似乎总是适用ScaleToFill。

知道为什么会这样吗？任何建议都非常感谢。

Answer 1

(1) Aspect Fit 确实拉伸图像 - 以适应。如果您根本不想拉伸图像，请使用 Center（例如）。

(2) imageWithCIImage 给你一个非常奇怪的野兽，一个不基于 CGImage 的 UIImage，因此不受图层显示的正常规则的影响。它实际上只是 CIImage 的一个薄包装，这不是您想要的。您必须通过 CGImage 将 CIFilter 输出转换（渲染）为 UIImage，从而为您提供一个实际上有一些位（CGImage，位图）的 UIImage。我在这里的讨论为您提供了演示代码：

http://www.apeth.com/iOSBook/ch15.html#_cifilter_and_ciimage

换句话说，在某些时候，您必须调用 CIContext createCGImage:fromRect: 从 CIFilter 的输出中生成 CGImageRef，并将其传递给 UIImage。在您这样做之前，您不会将过滤器操作的输出作为真正的 UIImage。

或者，您可以将图像从imageWithCIImage 绘制到图形上下文中。例如，您可以将其绘制到图像图形上下文中，然后使用 that 图像。

您不能做的是直接显示来自imageWithCIImage 的图像。那是因为它不是图像！它没有底层位图（CGImage）。那里没有。它只是一组用于导出图像的 CIFilter 指令。

Answer 2

这是 Swift 的答案，灵感来自 this question 和 the solution by user1951992。

let imageView = UIImageView(frame: CGRect(x: 100, y: 200, width: 100, height: 50))
imageView.contentMode = .scaleAspectFit

//just an example for a CIFilter
//NOTE: we're using implicit unwrapping here because we're sure there is a filter
//(and an image) named exactly this
let filter = CIFilter(name: "CISepiaTone")!
let image = UIImage(named: "image")!
filter.setValue(CIImage(image: image), forKey: kCIInputImageKey)
filter.setValue(0.5, forKey: kCIInputIntensityKey)

guard let outputCGImage = filter?.outputImage,
    let outputImage = CIContext().createCGImage(outputCGImage, from: outputCGImage.extent) else {
        return
}

imageView.image = UIImage(cgImage: outputImage)

Answer 3

我一整天都在这上面。我遇到了方向问题，然后是质量差的输出。

使用相机拍摄图像后，我会这样做。

NSData *imageData = [AVCaptureStillImageOutput jpegStillImageNSDataRepresentation:imageDataSampleBuffer];
                UIImage *image = [[UIImage alloc] initWithData:imageData];

这会导致旋转问题，所以我需要这样做。

UIImage *scaleAndRotateImage(UIImage *image)
{
    int kMaxResolution = image.size.height; // Or whatever

    CGImageRef imgRef = image.CGImage;

    CGFloat width = CGImageGetWidth(imgRef);
    CGFloat height = CGImageGetHeight(imgRef);

    CGAffineTransform transform = CGAffineTransformIdentity;
    CGRect bounds = CGRectMake(0, 0, width, height);
    if (width > kMaxResolution || height > kMaxResolution) {
        CGFloat ratio = width/height;
        if (ratio > 1) {
            bounds.size.width = kMaxResolution;
            bounds.size.height = bounds.size.width / ratio;
        }
        else {
            bounds.size.height = kMaxResolution;
            bounds.size.width = bounds.size.height * ratio;
        }
    }

    CGFloat scaleRatio = bounds.size.width / width;
    CGSize imageSize = CGSizeMake(CGImageGetWidth(imgRef), CGImageGetHeight(imgRef));
    CGFloat boundHeight;
    UIImageOrientation orient = image.imageOrientation;
    switch(orient) {

        case UIImageOrientationUp: //EXIF = 1
            transform = CGAffineTransformIdentity;
            break;

        case UIImageOrientationUpMirrored: //EXIF = 2
            transform = CGAffineTransformMakeTranslation(imageSize.width, 0.0);
            transform = CGAffineTransformScale(transform, -1.0, 1.0);
            break;

        case UIImageOrientationDown: //EXIF = 3
            transform = CGAffineTransformMakeTranslation(imageSize.width, imageSize.height);
            transform = CGAffineTransformRotate(transform, M_PI);
            break;

        case UIImageOrientationDownMirrored: //EXIF = 4
            transform = CGAffineTransformMakeTranslation(0.0, imageSize.height);
            transform = CGAffineTransformScale(transform, 1.0, -1.0);
            break;

        case UIImageOrientationLeftMirrored: //EXIF = 5
            boundHeight = bounds.size.height;
            bounds.size.height = bounds.size.width;
            bounds.size.width = boundHeight;
            transform = CGAffineTransformMakeTranslation(imageSize.height, imageSize.width);
            transform = CGAffineTransformScale(transform, -1.0, 1.0);
            transform = CGAffineTransformRotate(transform, 3.0 * M_PI / 2.0);
            break;

        case UIImageOrientationLeft: //EXIF = 6
            boundHeight = bounds.size.height;
            bounds.size.height = bounds.size.width;
            bounds.size.width = boundHeight;
            transform = CGAffineTransformMakeTranslation(0.0, imageSize.width);
            transform = CGAffineTransformRotate(transform, 3.0 * M_PI / 2.0);
            break;

        case UIImageOrientationRightMirrored: //EXIF = 7
            boundHeight = bounds.size.height;
            bounds.size.height = bounds.size.width;
            bounds.size.width = boundHeight;
            transform = CGAffineTransformMakeScale(-1.0, 1.0);
            transform = CGAffineTransformRotate(transform, M_PI / 2.0);
            break;

        case UIImageOrientationRight: //EXIF = 8
            boundHeight = bounds.size.height;
            bounds.size.height = bounds.size.width;
            bounds.size.width = boundHeight;
            transform = CGAffineTransformMakeTranslation(imageSize.height, 0.0);
            transform = CGAffineTransformRotate(transform, M_PI / 2.0);
            break;

        default:
            [NSException raise:NSInternalInconsistencyException format:@"Invalid image orientation"];

    }

    UIGraphicsBeginImageContext(bounds.size);

    CGContextRef context = UIGraphicsGetCurrentContext();

    if (orient == UIImageOrientationRight || orient == UIImageOrientationLeft) {
        CGContextScaleCTM(context, -scaleRatio, scaleRatio);
        CGContextTranslateCTM(context, -height, 0);
    }
    else {
        CGContextScaleCTM(context, scaleRatio, -scaleRatio);
        CGContextTranslateCTM(context, 0, -height);
    }

    CGContextConcatCTM(context, transform);

    CGContextDrawImage(UIGraphicsGetCurrentContext(), CGRectMake(0, 0, width, height), imgRef);
    UIImage *imageCopy = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();  

    return imageCopy;  
}

然后当我应用我的过滤器时，我会这样做（特别感谢这个线程 - 特别是 matt 和 Wex）

    -(UIImage*)processImage:(UIImage*)image {

            CIImage *inImage = [CIImage imageWithCGImage:image.CGImage];

            CIFilter *filter = [CIFilter filterWithName:@"CIColorControls" keysAndValues:
                        kCIInputImageKey, inImage,
                        @"inputContrast", [NSNumber numberWithFloat:1.0],
                        nil];

    UIImage *outImage = [filter outputImage];

//Juicy bit
            CGImageRef cgimageref = [[CIContext contextWithOptions:nil] createCGImage:outImage fromRect:[outImage extent]];

            return [UIImage imageWithCGImage:cgimageref];
        }