Graphics.GetHalftonePalette Method

Definition

Gets a handle to the current Windows halftone palette.

C#
public static IntPtr GetHalftonePalette();

Returns

IntPtr

Internal pointer that specifies the handle to the palette.

Examples

The following code example is designed for use with Windows Forms, and it requires PaintEventArgs e, which is a parameter of the Paint event handler. The code performs the following actions:

  • Defines interoperability DllImportAttribute attributes for the Windows DLL file gdi32.dll, which contains the necessary GDI functions.

  • Defines the SelectPalette and RealizePalette functions in that DLL as external.

  • Creates an image from an existing image file SampImag.jpg (which must be in the same folder as the example code file) and draws the image to the screen.

  • Creates internal pointer type variables and sets their values to the handle to the graphics object and to the current Windows halftone palette, respectively.

  • Selects and realizes the halftone palette.

  • Creates a new graphics object using the hdc parameter.

  • Draws the image again.

  • Releases the handle to the device context.

The result is two renderings of the sample image: one with the 16-bit palette and one with the 8-bit palette.

C#
[System.Runtime.InteropServices.DllImportAttribute("gdi32.dll")]
private static extern IntPtr SelectPalette(
    IntPtr hdc,
    IntPtr htPalette,
    bool bForceBackground);
[System.Runtime.InteropServices.DllImportAttribute("gdi32.dll")]
private static extern int RealizePalette(IntPtr hdc);

private void GetHalftonePaletteVoid(PaintEventArgs e)
{
    // Create and draw image.
    Image imageFile = Image.FromFile("SampImag.jpg");
    e.Graphics.DrawImage(imageFile, new Point(0, 0));

    // Get handle to device context.
    IntPtr hdc = e.Graphics.GetHdc();

    // Get handle to halftone palette.
    IntPtr htPalette = Graphics.GetHalftonePalette();

    // Select and realize new palette.
    SelectPalette(hdc, htPalette, true);
    RealizePalette(hdc);

    // Create new graphics object.
    Graphics newGraphics = Graphics.FromHdc(hdc);

    // Draw image with new palette.
    newGraphics.DrawImage(imageFile, 300, 0);

    // Release handle to device context.
    e.Graphics.ReleaseHdc(hdc);
}

Remarks

The purpose of the GetHalftonePalette method is to enable GDI+ to produce a better quality halftone when the display uses 8 bits per pixel. To display an image using the halftone palette, use the following procedure.

Applies to

Product Versions
.NET 8 (package-provided), 9 (package-provided)
.NET Framework 1.1, 2.0, 3.0, 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7 (package-provided), 4.7, 4.7.1 (package-provided), 4.7.1, 4.7.2 (package-provided), 4.7.2, 4.8 (package-provided), 4.8, 4.8.1
.NET Standard 2.0 (package-provided)
Windows Desktop 3.0, 3.1, 5, 6, 7, 8, 9