Color Model

The set of rules for manipulating color values in a processing system is sometimes called a color model. IVL supports a color model that is based on processing pixel values with red, green, blue, and alpha values, hence it is called RGBA mode. The color model is determined by characteristics of the window in which drawing is to occur. For this release of IVL, all windows that support IVL rendering support RGBA mode.

RGBA mode is based on the premise that the system supports the processing of up to four channels of color information simultaneously. The red, green, and blue components are always treated identically.

During processing, red, green, blue, and alpha values are conceptually treated as floating-point numbers in the range [0.0, 1.0]. As pixels are processed and converted into values that can be written into the frame buffer, a component value of 0.0 will be mapped into the smallest displayable frame buffer value, and a value of 1.0 will be mapped into the largest displayable frame buffer value.

In most cases, alpha values are treated the same as the other three components, but there are some differences in how alpha values are processed. However, the IVL specification permits implementations to streamline internal processing so long as doing so does not alter the resultant image. If the underlying frame buffer does not support the storage of an alpha channel, then the implementation may choose not to apply some image processing operations to the alpha data.

Many imaging applications manipulate and display images that contain only a single channel of color information. In IVL terminology, these images are referred to as luminance-only images, or simply luminance images. These luminance images can be thought of as RGBA images where the input luminance value is used as the red, green, and blue component value for each pixel. The alpha value defaults to 1.0 for every pixel.