objective-c – 如何获得有意义的CIAreaHistogram输出？

概述我想计算CG Image的直方图. 我正在使用CIAreaHistogram内置的CoreImage过滤器. Justin Mrkva做了something along similar lines.他说： I get the CIImage for the histogram itself, which I then run through a custom kernel (see end of 我想计算CG Image的直方图.
我正在使用CIAreaHistogram内置的CoreImage过滤器.

Justin Mrkva做了something along similar lines.他说：

I get the CIImage for the histogram itself,which I then run through a custom kernel (see end of post) to set Alpha values to 1 (since otherwise the Alpha value from the histogram calculations is premultiplIEd) and then convert it to an NSBitmAPImageRep.

我的问题是：是否有可能获得直方图数据而无需创建自定义内核？如果是这样,怎么样？

以下代码只是尝试渲染直方图而不修改Alpha值：

- (voID)printHistogram:(CGImageRef)img {    NSNumber* buckets = @10;    CIImage* img_ = [CIImage imageWithCGImage:img];    CIFilter* histF = [CIFilter filterWithname:@"CIAreaHistogram"];    [histF setValue:img_ forKey:@"inputimage"];    [histF setValue:[CIVector vectorWithX:0.0                                        Y:0.0                                        Z:CGImageGetWIDth(img)                                        W:CGImageGetHeight(img)]             forKey:@"inputExtent"];    [histF setValue:buckets forKey:@"inputCount"];    [histF setValue:@1.0 forKey:@"inputScale"];    CIImage* histimg = [histF valueForKey:@"outputimage"];    int rowBytes = [buckets intValue] * 4; // ARGB has 4 components    uint8_t byteBuffer[rowBytes]; // Buffer to render into    CGcolorSpaceRef cspace = CGcolorSpaceCreateWithname(kCGcolorSpaceGenericRGB);    CIContext* ctx = [[CIContext alloc] init];    [ctx render:histimg       toBitmap:byteBuffer       rowBytes:rowBytes         bounds:[histimg extent]         format:kCIFormatARGB8     colorSpace:cspace];    CGcolorSpaceRelease(cspace);    for (int i=0; i<[buckets intValue]; i++) {        const uint8_t* pixel = &byteBuffer[i*4];        printf("%d:%u-%u-%u-%u\n",i,pixel[0],pixel[1],pixel[2],pixel[3]);    }}

给出输出(当在彩色照片上运行时)：

0:0-0-0-01:0-0-0-02:0-0-0-03:0-0-0-04:0-0-0-05:0-0-0-06:0-0-0-07:0-0-0-08:0-0-0-09:255-33-6-7

我尝试使用CIcolorMatrix在渲染之前将Alpha值设置为1.0：

CIFilter* biasF = [CIFilter filterWithname:@"CIcolorMatrix"];[biasF setDefaults];[biasF setValue:histimg forKey:@"inputimage"];[biasF setValue:[CIVector vectorWithX:0.0 Y:0.0 Z:0.0 W:1.0] forKey:@"inputBiasvector"];

即使输出格式是ARGB,根据我从核心图像过滤器参考中所理解的,Alpha分量是向量中的最后一个值(因此W：1.0).

但是这产生了以下输出：

0:255-255-255-2551:255-255-255-2552:255-255-255-2553:255-255-255-2554:255-255-255-2555:255-255-255-2556:255-255-255-2557:255-255-255-2558:255-255-0-2559:255-66-11-15

所有的帮助和建议将不胜感激！

编辑：我知道this question似乎相似.但是,接受的答案规定：

The short of it is: you need to read the values as floats,not ints,which means you’ll have to hook up a CGBitmapContext to blit to. Or if you keep everything in CI land,you’ll need another filter to read the data and print something out with it.

但是,看看Justin Mrkva’s question让我觉得应该可以获得整数值…如果我的想法有误,请告诉我.

再次感谢！

编辑2：所有的拳头,感谢DavID和Jstn的评论.对不起,我花了很长时间才回到这里.我在一个项目上昼夜不停地工作(实际上是那个导致我遇到这个问题的项目,但我最终使用了一种完全不同的方法,不再使用CIAreaHistogram).现在我终于有了一些时间,我想回到这一点.即使我本身并不需要它,我仍然想要了解这个东西是如何工作的！

根据DavID Hayward的建议,我做了以下修改.

- (voID)printHistogram:(CGImageRef)img {    NSNumber* buckets = @10;    CIImage* img_ = [CIImage imageWithCGImage:img];    CIFilter* histF = [CIFilter filterWithname:@"CIAreaHistogram"];    [histF setValue:img_ forKey:@"inputimage"];    [histF setValue:[CIVector vectorWithX:0.0                                        Y:0.0                                        Z:CGImageGetWIDth(img)                                        W:CGImageGetHeight(img)]             forKey:@"inputExtent"];    [histF setValue:buckets forKey:@"inputCount"];    [histF setValue:@1.0 forKey:@"inputScale"];    CIImage* histimg = [histF valueForKey:@"outputimage"];    NSUInteger arraySize = [buckets intValue] * 4; // ARGB has 4 components    // CHANGE 1: Since I will be rendering in float values,I set up the    //           buffer using CGfloat    CGfloat byteBuffer[arraySize]; // Buffer to render into    // CHANGE 2: I wasn't supposed to call [[CIContext alloc] init]    //           this is a more proper way of getting the context    CIContext* ctx = [[NSGraphicsContext currentContext] CIContext];    // CHANGE 3: I use colorSpace:NulL to use the output cspace of the ctx    // CHANGE 4: Format is Now kCIFormatRGBAf    [ctx render:histimg       toBitmap:byteBuffer       rowBytes:arraySize         bounds:[histimg extent]         format:kCIFormatRGBAf     colorSpace:NulL]; // uses the output cspace of the contetxt    // CHANGE 5: I print the float values    for (int i=0; i<[buckets intValue]; i++) {        const CGfloat* pixel = &byteBuffer[i*4];        printf("%d: %0.2f,%0.2f,%0.2f\n",pixel[3]);    }}

这给出了以下输出：

0: 0.00,0.00,0.001: 0.00,0.002: 0.00,0.003: 0.00,0.004: 0.00,0.005: 0.00,0.006: 0.00,1.00,0.007: 0.00,0.008: 0.00,0.009: 3.00,0.00

使用各种格式以及如何解析信息会产生截然不同且荒谬的输出.

我很确定问题在于没有正确理解位图数据的表示方式.

还有什么建议？

解决方法 三点建议：

>使用inputScale获取直方图计数.如果inputScale为1,那么如果整个区域具有该bin值,则得到的直方图bin值将为1.0(如果呈现给ARGB8则为255)>传递CI的工作色彩空间来渲染：toBitmap：.在Mavericks上,工作空间是kCGcolorSpaceGenericRGBlinear.在优胜美地,它是线性sRGB.>在OS X上,您可以使用kCIFormatRGBAf来获取浮点数据>在iOS上,您可以使用kCIFormatRGBAh获取半浮点数据

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