Colour Depth Control

Source Code

vbMedia

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Colour Depth Control

Reduce the number of colours in an image and save bitmaps at the correct colour depth

NOTE: this code has been superceded by the version at the new site.

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Colour Depth Reduction Sample

Download the Colour Depth demonstration project (50kb)

Introduction
A VB StdPicture object can be passed to the SavePicture method in order to save it as a bitmap file on disk. However, this method will usually save bitmaps at the system colour depth, and you cannot specify whether you want to save to a different colour depth.

This sample shows how to colour reduce a DIBSection object using two different techniques and save that to a bitmap file at the correct colour depth.

Saving Bitmaps
The Bitmap file format, unlike compressed formats such as PNG and GIF, is straightforward:

   BITMAPFILEINFOHEADER structure

   BITMAPINFOHEADER structure

   If NumColors       array[0 to NumColors-1] of RGBQUAD structures
   End If

   Bitmap Bits, scan-aligned to a DWORD boundary.

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