Using Color Values in LEADTOOLS

The standard Windows values for COLORREF represent either red, green, and blue color values, or an index into the bitmap's palette. A COLORREF value with the format 0x00BBGGRR represents the blue, green, and red color values for the specified pixel, where 0xBB is the blue value, 0xGG is the green value and 0xRR is the red value. If 0x01000000 is set in the COLORREF value (0x010000ZZ), the lower 8 bits (0xZZ) represent an index into the bitmap's palette which holds the color value. These COLORREF values can be used with any Windows function and macro that takes a COLORREF parameter. Please note that just because a bitmap has a palette, that does not mean the returned COLORREF value is automatically an index.

In the Document and Medical Imaging toolkits the COLORREF value may represent a 16 bit grayscale value if pBitmap is a 12 or 16-bit grayscale bitmap. So that the value is not confused with an RGB value, the COLORREF_GRAY16 mask (0x04000000) is set. In this case (0x0400YYYY), the lower 16 bits (0xYYYY) of the COLORREF value represent the 16-bit grayscale value. This is not a standard Windows value. Therefore, LEADTOOLS functions will recognize a COLORREF having this format, but Windows functions will not. To use a COLORREF value of this type in a non-LEADTOOLS function, you must do the following:

COLORREF color; 
color = L_GetPixelColor(pBitmap, x, y); 
if(color & COLORREF_GRAY16) 
   // nonstandard colorref value, convert it to a windows COLORREF 
   // get an 8 bit gray value corresponding to the 16 bit gray value 
   L_UCHAR gray = (color & 0xFFFF) >> 8; 
   // use the standard windows RGB macro to get a windows COLORREF 
   color = RGB(gray, gray, gray); 

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LEADTOOLS Raster Imaging C API Help

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