“未识别的选择器”当尝试访问CIFilter的outputImage时

问题描述

我第一次尝试Core Image（在OS X，10.7.3上），我跑到一堵砖墙上。我确定这是一个愚蠢的我正在做，只是需要一个更熟悉的框架来指出我。

I'm experimenting with Core Image (on OS X, 10.7.3) for the first time and am running into a brick wall. I'm certain this is something silly I'm doing and just need someone more familiar with the framework to point it out to me.

考虑下面的代码（让我们规定 imageURL 是指向磁盘上的JPG的有效文件URL）：

Consider the following code (let's stipulate that imageURL is a valid file URL pointing to a JPG on disk):

CIImage *inputImage = [CIImage imageWithContentsOfURL:imageURL];
CIFilter *filter = [CIFilter filterWithName:@"CIAreaAverage" keysAndValues:
                                                  kCIInputImageKey, inputImage,
                                                  kCIInputExtentKey, [inputImage valueForKey:@"extent"],
                                                  nil];
CIImage *outputImage = (CIImage *)[filter valueForKey:@"outputImage"];

运行此代码时，最后一行会触发：

When running this code, the last line triggers:

0   CoreFoundation                      0x00007fff96c2efc6 __exceptionPreprocess + 198
1   libobjc.A.dylib                     0x00007fff9153cd5e objc_exception_throw + 43
2   CoreFoundation                      0x00007fff96cbb2ae -[NSObject doesNotRecognizeSelector:] + 190
3   CoreFoundation                      0x00007fff96c1be73 ___forwarding___ + 371
4   CoreFoundation                      0x00007fff96c1bc88 _CF_forwarding_prep_0 + 232
5   CoreImage                           0x00007fff8f03c38d -[CIAreaAverage outputImage] + 52
6   Foundation                          0x00007fff991d8384 _NSGetUsingKeyValueGetter + 62
7   Foundation                          0x00007fff991d8339 -[NSObject(NSKeyValueCoding) valueForKey:] + 392

现在，Core Image Filter Reference清楚地说明了CIAreaAverage 返回包含感兴趣区域的平均颜色的单像素图​​像。事实上，当我检查调试器中的过滤器属性（在尝试 valueForKey：调用之前）时，更令人困惑：

Now, the Core Image Filter Reference clearly states that CIAreaAverage "Returns a single-pixel image that contains the average color for the region of interest." Indeed, even more baffling, when I examine the filter attributes in the debugger (before trying the valueForKey: call):

(lldb) po [filter attributes]
(id) $3 = 0x00007fb3e3ef0e00 {
    CIAttributeDescription = "Calculates the average color for the specified area in an image, returning the result in a pixel.";
    CIAttributeFilterCategories =     (
        CICategoryReduction,
        CICategoryVideo,
        CICategoryStillImage,
        CICategoryBuiltIn
    );
    CIAttributeFilterDisplayName = "Area Average";
    CIAttributeFilterName = CIAreaAverage;
    CIAttributeReferenceDocumentation = "http://developer.apple.com/cgi-bin/apple_ref.cgi?apple_ref=//apple_ref/doc/filter/ci/CIAreaAverage";
    inputExtent =     {
        CIAttributeClass = CIVector;
        CIAttributeDefault = "[0 0 640 80]";
        CIAttributeDescription = "A rectangle that specifies the subregion of the image that you want to process.";
        CIAttributeDisplayName = Extent;
        CIAttributeType = CIAttributeTypeRectangle;
        CIUIParameterSet = CIUISetBasic;
    };
    inputImage =     {
        CIAttributeClass = CIImage;
        CIAttributeDescription = "The image to process.";
        CIAttributeDisplayName = Image;
        CIUIParameterSet = CIUISetBasic;
    };
    outputImage =     {
        CIAttributeClass = CIImage;
    };
}

有 outputImage 有 - 作为类型CIImage！

There's outputImage right there - given as type CIImage!

那么，我做错了什么？我看到的所有文档和教程指出 -valueForKey：是访问属性的正确方法，包括 outputImage 。

So, what am I doing wrong? All the docs and tutorials I have seen indicate that -valueForKey: is the correct way to access attributes, including outputImage.

推荐答案

我相信你的范围是罪魁祸首（不过很奇怪）。当我将区域更改为CIVector *时，它工作。

I believe your extents are the culprit (however strange it is). When I change the extents to be a CIVector* it works.

NSURL *imageURL = [NSURL fileURLWithPath:@"/Users/david/Desktop/video.png"];
CIImage *inputImage = [CIImage imageWithContentsOfURL:imageURL];
CIFilter *filter = [CIFilter filterWithName:@"CIAreaAverage"];
[filter setValue:inputImage forKey:kCIInputImageKey];
CGRect inputExtent = [inputImage extent];
CIVector *extent = [CIVector vectorWithX:inputExtent.origin.x
                                       Y:inputExtent.origin.y
                                       Z:inputExtent.size.width
                                       W:inputExtent.size.height];
[filter setValue:extent forKey:kCIInputExtentKey];
CIImage *outputImage = [filter valueForKey:@"outputImage"];

[inputImage extent]返回一个CGRect，但显然CIVector *效果更好。

[inputImage extent] returns an CGRect, but apparently a CIVector* works better.

这篇关于“未识别的选择器”当尝试访问CIFilter的outputImage时的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！