使用CIImage使所有黑色像素透明

Question

我正在尝试使用专门的CIImage滤镜来获得类似于颜色遮罩的东西.

基本上,我希望使所有黑色像素透明.我不介意所有非黑色像素的最终颜色,只要它们具有最大的alpha值.

我在Core Graphics中熟悉的代码实现这一点看起来像:

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

我已经使用彩色矩阵滤镜在Core Image中拍摄了一张照片,但由于CIVector值大于,因此它只是设置result为.nil1.0f

// 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:对于它的价值,这是一个OSX应用程序.

Answer 1

编辑

使用(简单)Custom 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Apple的方法文件的副本):

#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

自定义内核完成所有工作(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;
}

使用过滤器就像内置过滤器一样:

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

添加参数以选择要用作遮罩颜色的颜色应该没问题.

老答复

有了内置的方法和类,我只能想出这个相当不优雅的解决方案(它只使用Core Image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"];