C++ cv::Scalar 未显示预期颜色

cv::Scalar not displaying expected color

提问by Protocole

On an image frame, I use

在图像框架上，我使用

void ellipse(Mat& img, Point center, Size axes, double angle, double startAngle, double endAngle, const Scalar& color, int thickness=1, int lineType=8, int shift=0)

void ellipse(Mat& img, Point center, Size axes, double angle, double startAngle, double endAngle, const Scalar& color, int thickness=1, int lineType=8, int shift=0)

to draw an ellipse and I want to set the ellipse color to green [ RGB value : (165, 206, 94) ]. So I set the parameter const Scalar& colorto

绘制椭圆，我想将椭圆颜色设置为绿色 [ RGB 值 : (165, 206, 94) ]。所以我将参数设置const Scalar& color为

cv::Scalar(94.0, 206.0, 165.0, 0.0); // as BGR order, suppose the value is 0.0 - 255.0
cv::Scalar(94.0/255.0, 206.0/255.0, 165.0/255.0, 0.0); // suppose the value is 0.0 - 1.0

I also tried RGB alternative.

我也尝试过 RGB 替代品。

CV_RGB(165.0, 206.0, 94.0); // as RGB order, suppose the value is 0.0 - 255.0
CV_RGB(165.0/255.0, 206.0/255.0, 94.0/255.0); // suppose the value is 0.0 - 1.0

But the color being displayed is white [ RGB value (255, 255, 255) ] , not the desired green one.

但是显示的颜色是白色[ RGB value (255, 255, 255) ] ，而不是所需的绿色。

What I missed at this point? Any suggestion please. Thank you.

在这一点上我错过了什么？请提出任何建议。谢谢你。

EDIT:

编辑：

Let me put whole related code here. According to OpenCV iOS - Video Processing, this is the CvVideoCameraconfig in - (void)viewDidLoad;:

让我把完整的相关代码放在这里。根据OpenCV iOS-Video Processing，这是以下CvVideoCamera配置- (void)viewDidLoad;：

self.videoCamera = [[CvVideoCamera alloc] initWithParentView:imgView];
[self.videoCamera setDelegate:self];
self.videoCamera.defaultAVCaptureDevicePosition = AVCaptureDevicePositionFront;
self.videoCamera.defaultAVCaptureSessionPreset = AVCaptureSessionPreset352x288;
self.videoCamera.defaultAVCaptureVideoOrientation = AVCaptureVideoOrientationPortrait;
self.videoCamera.defaultFPS = 30;
self.videoCamera.grayscaleMode = NO;
[self.videoCamera adjustLayoutToInterfaceOrientation:UIInterfaceOrientationPortrait];

Then after [self.videoCamera start];called, the (Mat&)imagewould be captured and can be processed in the CvVideoCameraDelegate method - (void)processImage:(Mat&)image;and here are the code to draw an ellipse:

然后在[self.videoCamera start];调用后，(Mat&)image将被捕获​​并可以在 CvVideoCameraDelegate 方法中进行处理- (void)processImage:(Mat&)image;，这里是绘制椭圆的代码：

- (void)processImage:(Mat&)image {

NSLog(@"image.type(): %d", image.type()); // got 24

// image.convertTo(image, CV_8UC3); // try to convert image type, but with or without this line result the same

NSLog(@"image.type(): %d", image.type()); // also 24

cv::Scalar colorScalar = cv::Scalar( 94, 206, 165 );
cv::Point center( image.size().width*0.5, image.size().height*0.5 );
cv::Size size( 100, 100 );
cv::ellipse( image, center, size, 0, 0, 360, colorScalar, 4, 8, 0 );

}

}

Eventually, the ellipse is still in white, not the desired green one.

最终，椭圆仍然是白色的，而不是想要的绿色。

回答by PowHu

Set alpha to 255 can fix this problem. Scalar(94,206,165,255)

将 alpha 设置为 255 可以解决这个问题。标量(94,206,165,255)

回答by Barshan Das

As mrgloom points correctly in the comment, it might be because of type of your image [ the Mat object where you want to draw, i.e Mat &img in ellipse() function]. cv::Scalar(94, 206, 165) is the desired green color for 8UC3 type images. Setting these values in 32FC3 image will result in white color.

由于 mrgloom 在评论中正确指向，这可能是因为您的图像类型[您要绘制的 Mat 对象，即 ellipse() 函数中的 Mat &img]。cv::Scalar(94, 206, 165) 是 8UC3 类型图像所需的绿色。在 32FC3 图像中设置这些值将导致白色。

回答by theroom101

you can use

您可以使用

src.convertTo(src, CV_8UC3);

src.convertTo(src, CV_8UC3);

Where CV_8UC3 means that you use 8 bits unsigned char and 3 color image representation. More information you can find here OpenCV docsafter that your ellipse should be green, if it doesn't help post the whole code.

其中 CV_8UC3 表示您使用 8 位无符号字符和 3 色图像表示。您可以在此处找到OpenCV 文档的更多信息， 之后您的椭圆应该是绿色的，如果它对发布整个代码没有帮助。

回答by Shakir

I was having similar problem and I have managed to fix it by first converting image to BGR. So in your case processImage function would look like as:

我遇到了类似的问题，我设法通过首先将图像转换为 BGR 来解决它。所以在你的情况下 processImage 函数看起来像：

-(void)processImage:(Mat&)image
{
    cvtColor(image, image, CV_RGBA2BGR);
    cv::Scalar colorScalar = cv::Scalar( 94, 206, 165 );
    cv::Point center( image.size().width*0.5, image.size().height*0.5 );
    cv::Size size( 100, 100 );
    cv::ellipse( image, center, size, 0, 0, 360, colorScalar, 4, 8, 0 );
}

The only line which I have included in your code is:

我在您的代码中包含的唯一一行是：

cvtColor(image, image, CV_RGBA2BGR);

If you also log channel, depth and type information in the above function as follows:

如果您还在上述函数中记录通道、深度和类型信息，如下所示：

NSLog(@"Before conversion");
NSLog(@"channels %d", image.channels());
NSLog(@"depth %d", image.depth());
NSLog(@"type %d", image.type());
NSLog(@"element size %lu", image.elemSize());
cvtColor(image, image, CV_RGBA2BGR);
NSLog(@"After conversion");
NSLog(@"channels %d", image.channels());
NSLog(@"depth %d", image.depth());
NSLog(@"type %d", image.type());
NSLog(@"element size %lu", image.elemSize());

you will see before conversion:

转换前你会看到：

channels 4
depth 0
type 24
element size 4

which I think is CV_8UC4 and after conversion it becomes:

我认为是 CV_8UC4 转换后它变成：

channels 3
depth 0
type 16
element size 3

which is CV_8UC3.

这是 CV_8UC3。

I guess one of the reason why it does not work without cvtColor is that the opencv drawing functions don't support alpha transparency when the target image is 4-channel as mentioned in opencv documentation. So by converting CV_RGBA2BGR we take out alpha channel. However having said that I do not managed to get it work if I do:

我猜它在没有 cvtColor 的情况下不起作用的原因之一是当目标图像是opencv 文档中提到的 4 通道时，opencv 绘图函数不支持 alpha 透明度。所以通过转换 CV_RGBA2BGR 我们去掉了 alpha 通道。但是，话虽如此，如果我这样做，我就无法使其工作：

cvtColor(image, image, CV_RGBA2RGB);

In this Red and Blue colors are inverted in the image. So although it seems to work but I am not sure if it is the actual reason.

在这个图像中，红色和蓝色颜色是倒置的。所以虽然它似乎有效，但我不确定这是否是实际原因。