L_LTIMGCLR_API L_INT L_ColorLevelBitmap(pBitmap, pLvlClr, uFlags)
Applies color leveling to an image. It changes the image shadows, midtones and highlights.
Pointer to the bitmap handle.
Flag that indicates the channel being leveled. Possible values are:
|LEVEL_RED||[0x0001] Red channel|
|LEVEL_GREEN||[0x0010] Green channel|
|LEVEL_BLUE||[0x0100] Blue channel|
|LEVEL_MASTER||[0x1000] All channels|
|SUCCESS||The function was successful.|
|< 1||An error occurred. Refer to Return Codes.|
This function is useful for pre-processing images for the purpose of improving barcode recognition results.
Before calling the L_ColorLevelBitmap function, initialize the size and all remaining fields of the LVLCLRINF structures within the LVLCLR structure. These fields tell L_ColorLevelBitmap what constitutes shadows, midtones, and highlights and how to remap the shadows, midtones and highlights.
Control the amount of image balance and leveling by controlling the values of the nMinInput, nMaxInput, nMinOutput, nMaxOutput, and uGamma members of the LVLCLRINF structure contained in the
pLvlClr parameter. Keep in mind the following notes:
The nMinInput member of an LVLCLRINF structure defines what the function interprets as shadows for that color channel. Any value less than or equal to nMinInput is considered a shadow.
The nMaxInput member of an LVLCLRINF structure defines what the function interprets as highlights for that color channel. Any value greater than or equal to nMaxInput is considered a highlight.
The value of the nMaxInput member must be greater than the value of the nMinInput member by at least 2.
Midtones are those values between nMinInput and nMaxInput.
The nMinOutput member is the value to which the shadows will be mapped.
The nMaxOutput member is the value to which the highlights will be mapped.
The uGamma member is used to modify the midtone values
If only LEVEL_MASTER is set in
uFlags, then the rest of the channels will still be affected.
If the image is a grayscale image, set LEVEL_MASTER in uFlags (otherwise, the function will not have any effect).
If nMinOutput > nMaxOutput then the bitmaps shadows and highlights will be inverted.
To update a status bar or detect a user interrupt during execution of this function, refer to L_SetStatusCallback.
This function supports 12- and 16-bit grayscale and 48- and 64-bit color images. Support for 12- and 16-bit grayscale and 48- and 64-bit color images is available in the Document and Medical Imaging toolkits.
This function does not support 32-bit grayscale images. It returns the error code ERROR_GRAY32_UNSUPPORTED if a 32-bit grayscale image is passed to this function.
If the image has a region, the effect will be applied only on the region.
Required DLLs and Libraries
Win32, x64, Linux.
For complete sample code, refer to the CHILD.C module of the DEMO example. This example loads a bitmap and applies image leveling to it.
BITMAPHANDLE LeadBitmap; /* Bitmap handle to hold the loaded image. */
/* Load the bitmap, keeping the bits per pixel of the file */
nRet = L_LoadBitmap (MAKE_IMAGE_PATH(TEXT ("IMAGE1.CMP")), &LeadBitmap, sizeof(BITMAPHANDLE), 0, ORDER_BGR, NULL, NULL);
lvlClr.uStructSize = sizeof(LVLCLR);
/* Specify Image levels */
lvlClr.blue.nMinInput = 20;
lvlClr.blue.nMaxInput = 200;
lvlClr.blue.nMinOutput = 0;
lvlClr.blue.nMaxOutput = 255;
lvlClr.blue.uGamma = DEFAULT_GAMMA;
// Master will cause the image to be Inversed
lvlClr.master.nMinInput = 0;
lvlClr.master.nMaxInput = 255;
lvlClr.master.nMinOutput = 255;
lvlClr.master.nMaxOutput = 0;
lvlClr.master.uGamma = DEFAULT_GAMMA;
/* Level the Blue and Master channels */
nRet = L_ColorLevelBitmap (&LeadBitmap, &lvlClr, LEVEL_BLUE | LEVEL_MASTER);
nRet = L_SaveBitmap(MAKE_IMAGE_PATH(TEXT("Result.BMP")), &LeadBitmap, FILE_BMP, 24, 0, NULL);
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