ReduceToBitonal Method

Description:

Reduces an image from 24, 8, or 4 bpp to 1 bpp. Set Mode to specify how to get the threshold value.

If you set Mode to IG_REDUCE_BITONAL_WEIGHTED, you may also set the values of Weight1, Weight2, and Weight3. These "weights" are used to determine how much influence the values of the red, green, or blue pixels will have on the reduction. For example, if Weight1 (red) = 255, Weight2 (green) = 0, Weight3 (blue) = 0, the whole reduction will depend on the value of the red pixels. The green and blue pixel values will have "no weight."
IG_REDUCE_BITONAL_GRAYSCALE gives the most weight to the value of green. This optimizes for the perception of the human eye, in which blue is the hardest color to see, and therefore requires the least weight.
IG_REDUCE_BITONAL_AVE gives equal weight to all three pixel values.
Here are the formulas used by the three different reduction methods:
IG_REDUCE_BITONAL_GRAYSCALE: value = (red*77 + green*151 + blue*28)/256;
IG_REDUCE_BITONAL_AVE: value = (red + green + blue)/3;
IG_REDUCE_BITONAL_WEIGHTED: value = (red*w1 + green*w2 + blue*w3)/(w1 + w2 + w3);

Use the Threshold argument to set the threshold value for converting pixels to black or white. If the value, as calculated by one of the above reduction methods, is less than Threshold, the pixels will be set to black; if it is greater or equal to Threshold, the pixels will be set to white.

Syntax:

      ReduceToBitonal (ByVal pPage As IGPage, ByVal Mode As
enumIGBitonalReductModes, ByVal Threshold As Long, ByVal Weight1
As Long, ByVal Weight2 As Long, ByVal Weight3 As Long)

Parameters:

Name	Description
pPage	Reference to IGPage Object.
Mode	Specifies what type of reduction to perform.
Threshold	An integer value that specifies what pixel values will be changed to black, and which pixel values will be changed to white. Pixels with values greater than Threshold will be changed to white, and pixels that have values less than Threshold will be changed to black.
Weight1	These values are only used if Mode is set to IG_REDUCE_BITONAL_WEIGHTED. The range of values is 0 - 255. The default values are 255.
Weight2	The range of values is 0 - 255. The default values are 255.
Weight3	The range of values is 0 - 255. The default values are 255.

Return Value:

N/A

Bits Per Pixel:

4, 8, 24-bit input images; 1-bit output images

Sample:

Image Processing and Effects