Use the GetBitmapPixels helper routine to load the image's pixel values as RGBTriplet structures. Modify the pixel values and use SetBitmapPixels to update the image.

This program uses routines from the book to easily manipulate the pixels as RGBTriplet values.

' Get the picture's image.
GetBitmapPixels Picture1, pixels, bits_per_pixel

' Make RGBTriplet values for the new color.
If use_red Then
    to_pixel.rgbRed = 255
Else
    to_pixel.rgbBlue = 255
End If
use_red = Not use_red

wid = UBound(pixels, 1)
hgt = UBound(pixels, 2)
For Y = 0 To hgt - 1
    For X = 0 To wid - 1
        If (X \ 20) Mod 2 = (Y \ 20) Mod 2 Then
            pixels(X, Y) = black_pixel
        Else
            pixels(X, Y) = to_pixel
        End If
    Next X
Next Y

' Display the image.
SetBitmapPixels Picture1, bits_per_pixel, pixels
Picture1.Picture = Picture1.Image

• Fill a large area one pixel at a time using PSet (slowest)
• Fill a large area one pixel at a time using a Bitmap object in VB.NET (faster)
• Fill a large area one pixel at a time using SetDIBits (even faster)
• Fill a large area one pixel at a time using SetBitmapBits (fastest)