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#1 Posted : Thursday, April 20, 2017 6:18:25 PM(UTC)

Amin  
Amin

Groups: Manager, Tech Support
Posts: 357


The FeatherAlphaBlendCommand class and equivalent L_FeatherAlphaBlendBitmap() function are used for combining a foreground image on top of a background image using a grayscale mask.

If the mask has abrupt jumps from black to white, the blended pixels at these jumps could have some noise. To reduce that effect, a simple averaging of the mask image before blending will case the edges to become gradual changes, which in turn will produce smoother transitions at the corresponding blended pixels.

The following code was executed twice, the first without averaging the mask and the second with the averaging:
Code:
RasterCodecs rasterCodecs = new RasterCodecs();
//load foreground image
RasterImage imgBlended = rasterCodecs.Load("Blended.bmp");
//load background image
RasterImage imgBackground = rasterCodecs.Load("BackgroundDoc.tif");
//create blending mask
RasterImage imgMask = imgBlended.Clone();
//fill non-white in mask with pure black
imgMask.AddColorToRegion(RasterColor.White, RasterRegionCombineMode.SetNot);
FillCommand cmdFill = new FillCommand(RasterColor.Black);
cmdFill.Run(imgMask);
imgMask.MakeRegionEmpty();
GrayscaleCommand cmdGray = new GrayscaleCommand(8);
cmdGray.Run(imgMask);
InvertCommand cmdInvert = new InvertCommand();
cmdInvert.Run(imgMask);
var DoTheAveraging = MessageBox.Show("Perform averaging of the mask?", "Test Blending", MessageBoxButtons.YesNo);
if (DoTheAveraging == System.Windows.Forms.DialogResult.Yes)
{
   //smooth the mask
   AverageCommand cmdAvg = new AverageCommand(4);
   cmdAvg.Run(imgMask);
}
LeadRect rect = new LeadRect(500, 500, imgBlended.Width, imgBlended.Height);
FeatherAlphaBlendCommand cmdFeather = new FeatherAlphaBlendCommand(imgBlended, LeadPoint.Empty, rect, imgMask);
cmdFeather.Run(imgBackground);

The attached image shows the result in both cases.
blendresult.png

Edited by moderator Monday, April 24, 2017 11:01:52 AM(UTC)  | Reason: Not specified

Amin Dodin

Senior Support Engineer
LEAD Technologies, Inc.
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