SAMPLE: 16 and 32 Bits-Per-Pel Bitmap Formats

• Microsoft Win32 Application Programming Interface (API) included with:

      - Microsoft Windows NT versions 3.1, 3.5, and 3.51
      - Microsoft Windows 95 version 4.0
  

SUMMARY

Windows NT supports the same bitmap formats as Microsoft Windows version 3.1, but includes two new formats: 16 and 32 bits-per-pel.

SEEDIB.EXE is a file in the Microsoft Software Library that contains the source code to an application that demonstrates how to load, display, and save 1, 4, 8, 16, 24, and 32-bits-per-pixel DIB formats. In addition, it demonstrates a simple method of creating an optimized palette for displaying DIBSs with more than 8-bits-per-pixel on 8-bits-per-pixel devices.

NOTE: In order to minimize color loss, SeeDIB uses CreateDIBSection() to do conversions between uncompressed DIBs which have more than 8-bits-per- pixel. This function is not available on Windows NT 3.1.

You can download SEEDIB.EXE from the Microsoft Software Library (MSL) on the following services:

• Microsoft Download Service (MSDL)

        Dial (206) 936-6735 to connect to MSDL
        Download SEEDIB.EXE (size: 58950 bytes) 
  

• Internet (anonymous FTP)

        ftp ftp.microsoft.com
        Change to the \SOFTLIB\MSLFILES directory
        Get SEEDIB.EXE (size: 58950 bytes) 
  

MORE INFORMATION

For DIBs (device independent bitmaps), the 16 and 32-bit formats contain three DWORD masks in the bmiColors member of the BITMAPINFO structure. These masks specify which bits in the pel correspond to which color.

The three masks must have contiguous bits, and their order is assumed to be R, G, B (high bits to low bits). The order of the three masks in the color table must also be first red, then green, then blue (RGB). In this manner, the programmer can specify a mask indicating how many shades of each RGB color will be available for bitmaps created with CreateDIBitmap(). For 16-bits-per-pixel DIBs, CreateDIBitmap() defaults to the RGB555 format. For 32-bits-per-pixel DIBs, CreateDIBitmap() defaults to an RGB888 format.

NOTE: The DIB engine in Windows 95 supports only RGB555 and RGB565 for 16-bit DIBs and only RGB888 for 32-bit DIBs.

Example

The RGB555 format masks would look like:

   0x00007C00  red   (0000 0000 0000 0000 0111 1100 0000 0000)
   0x000003E0  green (0000 0000 0000 0000 0000 0011 1110 0000)
   0x0000001F  blue  (0000 0000 0000 0000 0000 0000 0001 1111)

The RGB888 format masks would look like:

   0x00FF0000  red   (0000 0000 1111 1111 0000 0000 0000 0000)
   0x0000FF00  green (0000 0000 0000 0000 1111 1111 0000 0000)
   0x000000FF  blue  (0000 0000 0000 0000 0000 0000 1111 1111)

Usage

When using 16 and 32-bit formats, there are also certain fields of the BITMAPINFOHEADER structure that must be set to the correct values:

1. The biCompression member must be set to either BI_RGB or BI_BITFIELDS. Using BI-RGB indicates that no bit masks are included in the color table and that the default (RGB555 for 16bpp and RGB888 for 32bpp) format is implied. Using BI_BITFIELDS indicates that there are masks (bit fields) specified in the color table.

2. As with 24-bits-per-pixel formats, the biClrUsed member specifies the size of the color table used to optimize performance of Windows color palettes. If the biCompression is set to BI_BITFIELDS, then the optimal color palette starts immediately following the three DWORD masks. Note that an optimal color palette is optional and many applications will ignore it.

Windows 95

In Windows 95, if the BI_BITFIELDS flag is set, then a color mask must be specified and it must be one of the following:

Resolution Bits per color Color Mask

16bpp       5,5,5           0x00007c00 0x000003e0 0x0000001f
16bpp       5,6,5           0x0000f800 0x000007e0 0x0000001f
32bpp       8,8,8           0x00ff0000 0x0000ff00 0x000000ff