Question

预定义：我的A4纸始终是白色的。

我需要从图像中检测A4纸。我能够检测矩形，现在的问题是我从图像中获取了多个矩形。因此，我从检测到的矩形点中提取了图像。

现在，我要使图像颜色与白色匹配。

使用以下方法从检测到的轮廓中提取图像：

- (cv::Mat) getPaperAreaFromImage: (std::vector<cv::Point>) square, cv::Mat image
{
    // declare used vars
    int paperWidth  = 210; // in mm, because scale factor is taken into account
    int paperHeight = 297; // in mm, because scale factor is taken into account
    cv::Point2f imageVertices[4];
    float distanceP1P2;
    float distanceP1P3;
    BOOL isLandscape = true;
    int scaleFactor;
    cv::Mat paperImage;
    cv::Mat paperImageCorrected;
    cv::Point2f paperVertices[4];

    // sort square corners for further operations
    square = sortSquarePointsClockwise( square );

    // rearrange to get proper order for getPerspectiveTransform()
    imageVertices[0] = square[0];
    imageVertices[1] = square[1];
    imageVertices[2] = square[3];
    imageVertices[3] = square[2];

    // get distance between corner points for further operations
    distanceP1P2 = distanceBetweenPoints( imageVertices[0], imageVertices[1] );
    distanceP1P3 = distanceBetweenPoints( imageVertices[0], imageVertices[2] );

    // calc paper, paperVertices; take orientation into account
    if ( distanceP1P2 > distanceP1P3 ) {
        scaleFactor =  ceil( lroundf(distanceP1P2/paperHeight) ); // we always want to scale the image down to maintain the best quality possible
        paperImage = cv::Mat( paperWidth*scaleFactor, paperHeight*scaleFactor, CV_8UC3 );
        paperVertices[0] = cv::Point( 0, 0 );
        paperVertices[1] = cv::Point( paperHeight*scaleFactor, 0 );
        paperVertices[2] = cv::Point( 0, paperWidth*scaleFactor );
        paperVertices[3] = cv::Point( paperHeight*scaleFactor, paperWidth*scaleFactor );
    }
    else {
        isLandscape = false;
        scaleFactor =  ceil( lroundf(distanceP1P3/paperHeight) ); // we always want to scale the image down to maintain the best quality possible
        paperImage = cv::Mat( paperHeight*scaleFactor, paperWidth*scaleFactor, CV_8UC3 );
        paperVertices[0] = cv::Point( 0, 0 );
        paperVertices[1] = cv::Point( paperWidth*scaleFactor, 0 );
        paperVertices[2] = cv::Point( 0, paperHeight*scaleFactor );
        paperVertices[3] = cv::Point( paperWidth*scaleFactor, paperHeight*scaleFactor );
    }

    cv::Mat warpMatrix = getPerspectiveTransform( imageVertices, paperVertices );
    cv::warpPerspective(image, paperImage, warpMatrix, paperImage.size(), cv::INTER_LINEAR, cv::BORDER_CONSTANT );

    if (true) {
        cv::Rect rect = boundingRect(cv::Mat(square));
        cv::rectangle(image, rect.tl(), rect.br(), cv::Scalar(0,255,0), 5, 8, 0);
        UIImage *object = [self UIImageFromCVMat:paperImage];
    }

    // we want portrait output
    if ( isLandscape ) {
        cv::transpose(paperImage, paperImageCorrected);
        cv::flip(paperImageCorrected, paperImageCorrected, 1);
        return paperImageCorrected;
    }

    return paperImage;
}

已编辑：我使用以下方法从图片中获取颜色。但是现在我将原始图像转换为cv :: mat之后的问题是，当我进行裁剪时，图像上已经有透明的灰色。所以我总是得到相同的颜色。

有没有直接方法可以从cv :: mat图像中获取原始颜色？

- (UIColor *)averageColor: (UIImage *) image {
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
unsigned char rgba[4];
CGContextRef context = CGBitmapContextCreate(rgba, 1, 1, 8, 4, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);

CGContextDrawImage(context, CGRectMake(0, 0, 1, 1), image.CGImage);
CGColorSpaceRelease(colorSpace);
CGContextRelease(context);

if(rgba[3] > 0) {
    CGFloat alpha = ((CGFloat)rgba[3])/255.0;
    CGFloat multiplier = alpha/255.0;
    return [UIColor colorWithRed:((CGFloat)rgba[0])*multiplier
                           green:((CGFloat)rgba[1])*multiplier
                            blue:((CGFloat)rgba[2])*multiplier
                           alpha:alpha];
}
else {
    return [UIColor colorWithRed:((CGFloat)rgba[0])/255.0
                           green:((CGFloat)rgba[1])/255.0
                            blue:((CGFloat)rgba[2])/255.0
                           alpha:((CGFloat)rgba[3])/255.0];
}
}

编辑2 ：输入图片

获取此输出

只需要检测A4白色。

Answer 1

我刚刚使用Google Vision API解决了该问题。

我的目标是从图像中计算出用于建造者的裂缝，因此在我的情况下，用户将在裂缝所在的图像上使用A4纸作为参考，然后捕获A4纸并计算每个像素所占的大小。然后，构建将在裂缝中点击两个点，然后我将计算出距离。

在google vision中，我使用了文档文本检测API，并将我的应用名称打印在完全垂直或水平覆盖的A4纸上。谷歌视觉API会检测到该文本并为我提供坐标。

使用OpenCV从图像中提取颜色

1 个答案: