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When I render the control to a memory DC, why is the bitmaps RGB values pre-multiplied?

April 26, 2017bitmap CONTROL dc memory pre-multiplied render RGB values

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When I render the control to a memory DC, why is the bitmaps RGB values pre-multiplied?

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The control’s PaintPicture method and the Picture.Render method use GDI+ rendering APIs to paint the image. Those APIs will premultiply the information in the bitmap when the bitmap is at a depth of 32 bit and exists in a memory DC. Though a majority of applications cannot or do not recognize premultiplied values, the control can and does. Recommend using AlphaBlend vs BitBlt when painting from a 32 bit DIB.