Merge pull request #10575 from ioxp:getFontScale

modules/imgproc/include/opencv2/imgproc.hpp

@@ -4730,6 +4730,20 @@ CV_EXPORTS_W Size getTextSize(const String& text, int fontFace,
                             double fontScale, int thickness,
                             CV_OUT int* baseLine);
 
+
+/** @brief Calculates the font-specific size to use to achieve a given height in pixels.
+
+@param fontFace Font to use, see cv::HersheyFonts.
+@param pixelHeight Pixel height to compute the fontScale for
+@param thickness Thickness of lines used to render the text.See putText for details.
+@return The fontSize to use for cv::putText
+
+@see cv::putText
+*/
+CV_EXPORTS_W double getFontScaleFromHeight(const int fontFace,
+                                           const int pixelHeight,
+                                           const int thickness = 1);
+
 /** @brief Line iterator
 
 The class is used to iterate over all the pixels on the raster line

modules/imgproc/src/drawing.cpp

@@ -2364,6 +2364,17 @@ Size getTextSize( const String& text, int fontFace, double fontScale, int thickn
     return size;
 }
 
+double getFontScaleFromHeight(const int fontFace, const int pixelHeight, const int thickness)
+{
+    // By https://stackoverflow.com/a/27898487/1531708
+    const int* ascii = getFontData(fontFace);
+
+    int base_line = (ascii[0] & 15);
+    int cap_line = (ascii[0] >> 4) & 15;
+
+    return static_cast<double>(pixelHeight - static_cast<double>((thickness + 1)) / 2.0) / static_cast<double>(cap_line + base_line);
+}
+
 }