Using the Minmax Part of the Histogram Extension

Using the Minmax Part of the Histogram Extension

The minmax part of the histogram extension lets you find out about minimum and maximum color component values present in an image. Using the minmax part of the histogram extension is similar to using the histogram part.

To determine minimum and maximum color values used in an image, follow these steps:

Specify a minmax table by calling glMinmaxEXT().
void glMinmaxEXT( GLenum target, GLenum internalformat, GLboolean sink)
- target is the table in which the information about the image is to be stored. target must be GL_MINMAX_EXT.
- internalformat specifies the format of the table entries. It must be an allowed internal format (see the reference page for glMinmaxEXT).
- sink is set to GL_TRUE or GL_FALSE. If GL_TRUE, no further processing happens and pixels or texels are discarded.
  The resulting minmax table always has two entries. Entry 0 is the minimum and entry 1 is the maximum.
Enable minmax by calling
glEnable(GL_MINMAX_EXT)
Perform the pixel operations, for example, glCopyPixels().
Each component of the internal format of the minmax table is compared to the corresponding component of the incoming RGBA pixel (luminance components are compared to red).
- If a component is greater than the corresponding component in the maximum element, then the maximum element is updated with the pixel component value.
- If a component is smaller than the corresponding component in the minimum element, then the minimum element is updated with the pixel component value.
Query the current context of the minmax table by calling glGetMinMaxExt():
void glGetMinMaxEXT ( GLenum target, GLboolean reset, GLenum format,
GLenum type, glvoid *values)

You can also call glGetMinmaxParameterEXT() to retrieve minmax state information; setting target to GL_MINMAX_EXT and pname to one of the following values:

GL_MINMAX_FORMAT_EXT: internal format of minmax table
GL_MINMAX_SINK_EXT: value of sink parameter