CIPixellate图像输出大小变化

Question

我正在用CIPixellate过滤器做一些测试，我让它正常工作，但是产生的图像大小不同。我认为这是合理的，因为我正在改变输入刻度，但这不是我所期望的-我以为它会在图像的正向范围内缩放。

我是误解了/使用了过滤器，还是只需要将输出图像裁剪到我想要的大小。

另外，从头/试和错误来看，inputCenter参数对我来说并不清楚。有人能解释一下这是怎么回事吗？

NSMutableArray * tmpImages = [[NSMutableArray alloc] init];
for (int i = 0; i < 10; i++) {
    double scale = i * 4.0;
    UIImage* tmpImg = [self applyCIPixelateFilter:self.faceImage withScale:scale];
    printf("tmpImg    width: %f height: %f\n",  tmpImg.size.width, tmpImg.size.height);
    [tmpImages addObject:tmpImg];
}

tmpImg    width: 480.000000 height: 640.000000
tmpImg    width: 484.000000 height: 644.000000
tmpImg    width: 488.000000 height: 648.000000
tmpImg    width: 492.000000 height: 652.000000
tmpImg    width: 496.000000 height: 656.000000
tmpImg    width: 500.000000 height: 660.000000
tmpImg    width: 504.000000 height: 664.000000
tmpImg    width: 508.000000 height: 668.000000
tmpImg    width: 512.000000 height: 672.000000
tmpImg    width: 516.000000 height: 676.000000

- (UIImage *)applyCIPixelateFilter:(UIImage*)fromImage withScale:(double)scale
{
    /*
     Makes an image blocky by mapping the image to colored squares whose color is defined by the replaced pixels.
     Parameters

     inputImage: A CIImage object whose display name is Image.

     inputCenter: A CIVector object whose attribute type is CIAttributeTypePosition and whose display name is Center.
     Default value: [150 150]

     inputScale: An NSNumber object whose attribute type is CIAttributeTypeDistance and whose display name is Scale.
     Default value: 8.00
     */
    CIContext *context = [CIContext contextWithOptions:nil];
    CIFilter *filter= [CIFilter filterWithName:@"CIPixellate"];
    CIImage *inputImage = [[CIImage alloc] initWithImage:fromImage];
    CIVector *vector = [CIVector vectorWithX:fromImage.size.width /2.0f Y:fromImage.size.height /2.0f];
    [filter setDefaults];
    [filter setValue:vector forKey:@"inputCenter"];
    [filter setValue:[NSNumber numberWithDouble:scale] forKey:@"inputScale"];
    [filter setValue:inputImage forKey:@"inputImage"];

    CGImageRef cgiimage = [context createCGImage:filter.outputImage fromRect:filter.outputImage.extent];
    UIImage *newImage = [UIImage imageWithCGImage:cgiimage scale:1.0f orientation:fromImage.imageOrientation];

    CGImageRelease(cgiimage);

    return newImage;
}

Answer 1

问题是只对进行缩放。

只需做：

let result = UIImage(cgImage: cgimgresult!, scale: (originalImageView.image?.scale)!, orientation: (originalImageView.image?.imageOrientation)!)
            originalImageView.image = result

Answer 2

正如苹果核心图像编程指南和这个职位所提到的，

默认情况下，模糊滤波器还通过模糊图像像素以及(在滤波器的图像处理空间中)包围图像的透明像素来软化图像的边缘。

所以你的输出图像会根据你的比例而变化。

对于inputCenter，正如约书亚·沙利文在这个在CIFilter上发布的注释中提到的，“它从源图像中调整像素网格的偏移量”。因此，如果inputCenter坐标不是CI像素inputScale的倍数，它将略微抵消像素平方(大部分在inputScale的大值上可见)。

Answer 3

有时，inputScale会不均匀地分割您的图像，这是当我发现我得到不同大小的输出图像时。

例如，如果inputScale =0或1，则输出图像大小非常精确。

我发现图像周围的额外空间居中的方式因inputCenter的“不透明”而异。呃，我还没花时间弄清楚到底是怎么回事(我把它通过点击位置设置在视图中)。

我对不同尺寸的解决方案是将图像重新渲染成输入图像的大小，这样做时我会为Apple Watch提供一个黑色的背景。

CIFilter *pixelateFilter = [CIFilter filterWithName:@"CIPixellate"];
[pixelateFilter setDefaults];
[pixelateFilter setValue:[CIImage imageWithCGImage:editImage.CGImage] forKey:kCIInputImageKey];
[pixelateFilter setValue:@(amount) forKey:@"inputScale"];
[pixelateFilter setValue:vector forKey:@"inputCenter"];
CIImage* result = [pixelateFilter valueForKey:kCIOutputImageKey];    
CIContext *context = [CIContext contextWithOptions:nil];
CGRect extent = [pixelateResult extent];
CGImageRef cgImage = [context createCGImage:result fromRect:extent];

UIGraphicsBeginImageContextWithOptions(editImage.size, YES, [editImage scale]);
CGContextRef ref = UIGraphicsGetCurrentContext();
CGContextTranslateCTM(ref, 0, editImage.size.height);
CGContextScaleCTM(ref, 1.0, -1.0);

CGContextSetFillColorWithColor(ref, backgroundFillColor.CGColor);
CGRect drawRect = (CGRect){{0,0},editImage.size};
CGContextFillRect(ref, drawRect);
CGContextDrawImage(ref, drawRect, cgImage);
UIImage* filledImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
returnImage = filledImage;

CGImageRelease(cgImage);

如果您要坚持您的实现，我建议您至少改变提取UIImage的方式，以使用原始图像的“比例”，而不是将其与CIFilter标度混淆。

UIImage *newImage = [UIImage imageWithCGImage:cgiimage scale:fromImage.scale orientation:fromImage.imageOrientation];