使用CIImage使所有黑色像素透明

Question

我正试图获得类似于只使用CIImage过滤器的彩色遮罩的东西。

基本上，我希望所有的黑色像素都是透明的。我不介意所有非黑色像素最终会有什么颜色，只要它们有最大的alpha。

我在Core Graphics中熟悉的实现这一目标的代码看起来像：

// Convert black sections to transparent using a color mask
const CGFloat maskingColors[6] = { 0, 0, 0, 0, 0, 0 };
CGImageRef result = CGImageCreateWithMaskingColors(image, maskingColors);

我在Core Image中使用了一个彩色矩阵滤波器对其进行了拍摄，但它只是将result设置为nil，因为CIVector值大于1.0f。

// Create color matrix filter
CIFilter *matrix = [CIFilter filterWithName:@"CIColorMatrix"];
// Set filter properties
[matrix setValue:image forKey:kCIInputImageKey];
[matrix setValue:[CIVector vectorWithX:1.0f Y:0.0f Z:0.0f W:0.0f] forKey:@"inputRVector"];
[matrix setValue:[CIVector vectorWithX:0.0f Y:1.0f Z:0.0f W:0.0f] forKey:@"inputGVector"];
[matrix setValue:[CIVector vectorWithX:0.0f Y:0.0f Z:1.0f W:0.0f] forKey:@"inputBVector"];
[matrix setValue:[CIVector vectorWithX:255.0f Y:255.0f Z:255.0f W:0.0f] forKey:@"inputAVector"];
// Get the mapped image
CIImage *result = [matrix valueForKey:kCIOutputImageKey];

注意：就其价值而言，这是一个OSX应用程序

Answer 1

编辑

使用（简单）自定义CIFilter的解决方案。此方法仅适用于OSX，因为iOS不支持自定义过滤器：

CIFilter子类（或多或少是苹果的How To的副本）：

#import <QuartzCore/QuartzCore.h>
@interface MaskFilter : CIFilter {
    CIImage *inputImage;
}
@end
@implementation MaskFilter
static CIKernel *maskFilterKernel = nil;
+ (void)initialize {
    [CIFilter registerFilterName: @"MaskFilter"
                     constructor: (id)self
                 classAttributes: [NSDictionary dictionaryWithObjectsAndKeys:
                                   @"Mask Filter", kCIAttributeFilterDisplayName,
                                   [NSArray arrayWithObjects:
                                    kCICategoryColorAdjustment,
                                    kCICategoryStillImage, kCICategoryInterlaced,
                                    kCICategoryNonSquarePixels,nil], kCIAttributeFilterCategories,
                                   nil]
     ];
}
+ (CIFilter *)filterWithName:(NSString *)name {
    CIFilter  *filter;
    filter = [[self alloc] init];
    return filter;
}
- (id)init {
    if(maskFilterKernel == nil) {
        NSBundle *bundle = [NSBundle bundleForClass:[self class]];
        NSString *code = [NSString stringWithContentsOfFile:[bundle pathForResource:@"MaskFilter" ofType: @"cikernel"] encoding:NSUTF8StringEncoding error:nil];
        NSArray *kernels = [CIKernel kernelsWithString:code];
        maskFilterKernel = [kernels objectAtIndex:0];
    }
    return [super init];
}
- (CIImage *)outputImage {
    CISampler *src = [CISampler samplerWithImage: inputImage];
    return [self apply:maskFilterKernel, src, kCIApplyOptionDefinition, [src definition], nil];
}
@end

完成所有工作的自定义内核（文件名：MaskFilter.cikernel）

kernel vec4 maskFilterKernel(sampler src) 
{
    vec4 t = sample(src, destCoord());
    t.w = (t.x == 0.0 ? (t.y == 0.0 ? (t.z == 0.0 ? 0.0 : 1.0) : 1.0) : 1.0);
    return t;
}

使用Filter的工作原理就像内置的Filter:

CIFilter *filter = [MaskFilter filterWithName:@"MaskFilter"];
[filter setValue:ciImage forKey:@"inputImage"];
CIImage *mask = [filter valueForKey: @"outputImage"];

添加一个参数来选择要用作遮罩颜色的颜色应该没有问题。

旧答案

有了内置的方法和类，我只能想出这个相当不合法的解决方案（它只使用核心图像过滤器）：

// convert all colors so they are brighter or equal to 0.5, except black
CIFilter *binary = [CIFilter filterWithName:@"CIColorMatrix"];
[binary setValue:inputImage forKey:@"inputImage"];
[binary setValue:[CIVector vectorWithX:1 Y:1 Z:1 W:0] forKey:@"inputRVector"];
[binary setValue:[CIVector vectorWithX:1 Y:1 Z:1 W:0] forKey:@"inputGVector"];
[binary setValue:[CIVector vectorWithX:1 Y:1 Z:1 W:0] forKey:@"inputBVector"];
[binary setValue:[CIVector vectorWithX:0.49999 Y:0.49999 Z:0.49999 W:0] forKey:@"inputBiasVector"];
inputImage = [binary valueForKey:@"outputImage"];
// convert to black/white only colors
binary = [CIFilter filterWithName:@"CIColorPosterize"];
[binary setDefaults];
[binary setValue:inputImage forKey:@"inputImage"];
[binary setValue:@2 forKey:@"inputLevels"];
inputImage = [binary valueForKey:@"outputImage"];
// get mask
CIFilter *mask = [CIFilter filterWithName:@"CIMaskToAlpha"];
[mask setDefaults];
[mask setValue: inputImage forKey:@"inputImage"];

Answer 2

它将黑色转换为透明，将任何其他颜色转换为白色

    func filteredImage(cgImage: CGImage) -> UIImage {
        if let matrixFilter = CIFilter(name: "CIColorMatrix") {
            matrixFilter.setDefaults()
            matrixFilter.setValue(CIImage(cgImage: cgImage), forKey: kCIInputImageKey)
            let rgbVector = CIVector(x: 0, y: 0, z: 0, w: 0)
            let aVector = CIVector(x: 1, y: 1, z: 1, w: 0)
            matrixFilter.setValue(rgbVector, forKey: "inputRVector")
            matrixFilter.setValue(rgbVector, forKey: "inputGVector")
            matrixFilter.setValue(rgbVector, forKey: "inputBVector")
            matrixFilter.setValue(aVector, forKey: "inputAVector")
            matrixFilter.setValue(CIVector(x: 1, y: 1, z: 1, w: 0), forKey: "inputBiasVector")
            if let matrixOutput = matrixFilter.outputImage, let cgImage = CIContext().createCGImage(matrixOutput, from: matrixOutput.extent) {
                return UIImage(cgImage: cgImage)
            }
        }
        return self
    }
}