如何直角座標到圖像座標FreeType中

Question

近日轉換，我在中國的文字措辭上的OCR，我想用的FreeType（2.3.5）收集字符的樣本，這裏是我的代碼：

FT_Library fontLibrary; 
FT_Face fontFace; 
int fontSize = 64; 

// Initialize 
FT_Init_FreeType(&fontLibrary); 
FT_New_Face(fontLibrary, "C:\\Windows\\Fonts\\simhei.ttf", 0, &fontFace); 

// Setup 
FT_Select_Charmap(fontFace, FT_ENCODING_UNICODE); 
FT_Set_Pixel_Sizes(fontFace, fontSize, 0); 
FT_Load_Char(fontFace, 'H', FT_LOAD_RENDER); 

// Retrieve data 
FT_GlyphSlot & glyphSlot = fontFace->glyph; 
FT_Bitmap charBitmap = glyphSlot->bitmap; 
int charWidth = charBitmap.width; 
int charHeight = charBitmap.rows; 
unsigned char* charBuffer = charBitmap.buffer; 

// Construct image 
Mat fontImage(fontSize, fontSize, CV_8UC1); 
fontImage = Scalar::all(0); 
for (int y = 0; y < charHeight; y++) 
{ 
    int row = fontSize - glyphSlot->bitmap_top + y; 
    for (int x = 0; x < charWidth; x++) 
    { 
     int col = glyphSlot->bitmap_left + x; 
     fontImage.at<uchar>(row, col) = charBuffer[y*charWidth + x]; 
    } 
} 

imshow("Font Image", fontImage); 
waitKey(0); 

// Uninitialize 
FT_Done_Face(fontFace); 
FT_Done_FreeType(fontLibrary); 

的問題是：該字符被未中心圖像對齊，字符圖像的座標看起來很奇怪，在這個例子中，「H」字符的座標（fontSize的= 64）：

bitmap_left = 3 
bitmap_top = 44 
bitmap.width = 26 
bitmap.rows = 43 

然後將轉換爲圖像的座標：

ROI.left = bitmap_left = 3; 
ROI.right = bitmap_left + bitmap.width = 29; 
ROI.top = fontSize - bitmap_top = 20; 
ROI.bottom = fontSize - bitmap_top + bitmap.rows = 63; 

所以在4方向上的餘量是：

ROI.leftMargin = 3; 
ROI.rightMargin = 64 - 29 = 35; 
ROI.topMargin = 20; 
ROI.bottomMargin = 64 - 63 = 1; 

IT IS NOT中心對準!!!

Answer 1

我解決了自己的問題，左頂部圖像的座標存儲在glyphSlot，這裏的博客： http://kang.blog.com/2013/09/21/how-to-convert-the-cartier-coordinate-to-image-coordinate-in-freetype/