来自iOS相机的亮度 [英] Luminosity from iOS camera

问题描述

我正在尝试制作应用程序，我必须像这个应用程序一样计算相机的亮度： http://itunes.apple.com/us/app/megaman-luxmeter/id455660266?mt=8

<我找到了这个文件： http://b2cloud.com。 au / tutorial / getting-luminosity-from-an-ios-camera

但我不知道如何直接适应相机而不是一个图像。这是我的代码：

  Image = [[UIImagePickerController alloc] init]; 
 Image.delegate = self; 
 Image.sourceType = UIImagePickerControllerCameraCaptureModeVideo; 
 Image.showsCameraControls = NO; 
 [Image setWantsFullScreenLayout：YES]; 
 Image.view.bounds = CGRectMake（0,0,320,480）; 
 [self.view addSubview：Image.view]; 
 
 NSArray * dayArray = [NSArray arrayWithObjects：Image，nil]; 
 for（NSString * day in dayArray）
 {
 for（int i = 1; i< = 2; i ++）
 {
 UIImage * image = [UIImage imageNamed：[NSString stringWithFormat：@％@％d.png，day，i]]; 
 unsigned char * pixels = [image rgbaPixels]; 
 double totalLuminance = 0.0; 
 for（int p = 0; p< image.size.width * image.size.height * 4; p + = 4）
 {
 totalLuminance + = pixels [p] * 0.299 +像素[p + 1] * 0.587 +像素[p + 2] * 0.114; 
} 
 totalLuminance / =（image.size.width * image.size.height）; 
 totalLuminance / = 255.0; 
 NSLog（@％@（％d）=％f，day，i，totalLuminance）; 
} 
} 
  

以下是问题：

未找到实例方法'-rgbaPixels'（返回类型默认为'id'）
&
不兼容的指针类型初始化'unsigned char *'，表达式为'id'

非常感谢！ =）

解决方案

让我建议一种替代方法，而不是对输入视频帧中每个像素进行昂贵的CPU绑定处理。我的开源 GPUImage 框架内置了一个光度提取器，它使用基于GPU的处理来提供直播来自摄像机的光度读数。

设置它相对容易。您只需分配一个GPUImageVideoCamera实例来表示相机，分配GPUImageLuminosity过滤器，并将后者添加为前者的目标。如果要将摄像头源显示到屏幕，请创建GPUImageView实例并将其添加为GPUImageVideoCamera的另一个目标。

您的光度提取器将使用回调块返回计算时的亮度值。使用以下代码设置此块：

  [（GPUImageLuminosity *）filter setLuminosityProcessingFinishedBlock：^（CGFloat luminosity，CMTime frameTime ）{
 //用亮度
}做一些事情}; 
  

我在这个答案，如果你很好奇。这个提取器在iPhone 4上运行大约6毫秒，用于640x480帧的视频。

你很快就会发现iPhone相机的平均光度是启用自动曝光时，几乎总是约50％。这意味着您需要使用相机元数据中的曝光值来补充光度测量值，以获得任何有意义的亮度测量值。

I'm trying to make an application and i have to calculate the brightness of the camera like this application : http://itunes.apple.com/us/app/megaman-luxmeter/id455660266?mt=8

I found this document : http://b2cloud.com.au/tutorial/obtaining-luminosity-from-an-ios-camera

But i don't know how to adapt it to the camera directly and not an image. Here is my code :

    Image = [[UIImagePickerController alloc] init];
    Image.delegate = self;
    Image.sourceType = UIImagePickerControllerCameraCaptureModeVideo;
    Image.showsCameraControls = NO;
    [Image setWantsFullScreenLayout:YES];
    Image.view.bounds = CGRectMake (0, 0, 320, 480);
    [self.view addSubview:Image.view];

    NSArray* dayArray = [NSArray arrayWithObjects:Image,nil];
    for(NSString* day in dayArray)
    {
        for(int i=1;i<=2;i++)
        {
            UIImage* image = [UIImage imageNamed:[NSString stringWithFormat:@"%@%d.png",day,i]];
            unsigned char* pixels = [image rgbaPixels];
            double totalLuminance = 0.0;
            for(int p=0;p<image.size.width*image.size.height*4;p+=4)
            {
                totalLuminance += pixels[p]*0.299 + pixels[p+1]*0.587 + pixels[p+2]*0.114;
            }
            totalLuminance /= (image.size.width*image.size.height);
            totalLuminance /= 255.0;
            NSLog(@"%@ (%d) = %f",day,i,totalLuminance);
        }
    }

Here are the issues :

"Instance method '-rgbaPixels' not found (return type defaults to 'id')" & "Incompatible pointer types initializing 'unsigned char *' with an expression of type 'id'"

Thanks a lot ! =)

解决方案

Rather than doing expensive CPU-bound processing of each pixel in an input video frame, let me suggest an alternative approach. My open source GPUImage framework has a luminosity extractor built into it, which uses GPU-based processing to give live luminosity readings from the video camera.

It's relatively easy to set this up. You simply need to allocate a GPUImageVideoCamera instance to represent the camera, allocate a GPUImageLuminosity filter, and add the latter as a target for the former. If you want to display the camera feed to the screen, create a GPUImageView instance and add that as another target for your GPUImageVideoCamera.

Your luminosity extractor will use a callback block to return luminosity values as they are calculated. This block is set up using code like the following:

[(GPUImageLuminosity *)filter setLuminosityProcessingFinishedBlock:^(CGFloat luminosity, CMTime frameTime) {
     // Do something with the luminosity
   }];

I describe the inner workings of this luminosity extraction in this answer, if you're curious. This extractor runs in ~6 ms for a 640x480 frame of video on an iPhone 4.

One thing you'll quickly find is that the average luminosity from the iPhone camera is almost always around 50% when automatic exposure is enabled. This means that you'll need to supplement your luminosity measurements with exposure values from the camera metadata to obtain any sort of meaningful brightness measurement.

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