如何在FreeType中將笛卡爾坐標轉換為圖像坐標

Question

最近，我用漢字寫OCR字樣，我想使用FreeType（2.3.5）收集字符樣本，這是我的代碼：

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);

問題是：字符在圖像中未居中對齊 ，字符圖像的坐標看起來很奇怪，在此示例中， “ H”字符的坐標為（fontSize = 64）：

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

然后轉換為圖像的坐標：

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;

因此4方向的邊距為：

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

它沒有中心對齊！

Answer 1

我自己解決了問題，圖像的左上角坐標存儲在glyphSlot中 ，這是博客： http : //kang.blog.com/2013/09/21/how-to-convert-the-cartier-coordinate 圖像坐標自由型/