VisionX V4    Subject Index Ordered Index General Info. Home Color and Multichannel VisionX V4

Multichannel and color files
VisionX images may contain more than one channel of information. The most usual uses of channel information are for color images (3 channels: red, green and blue) and complex numbers (2 channels: real and imaginary). In addition, for color images, an 8-bit index pixel format is available which requires a color table to define up to 256 possible colors. Many VisionX commands, especially those that involve numeric calculations, do not process multichannel or index format images. In these cases vchan can be used to select channels for processing and to reconstruct multichannel files.

Color index images
Color images are usually stored in either a 3 byte (RGB) format or in a byte index-pixel format. For color images a number of commands are available to convert between these two different formats. The following table lists some useful conversion commands. When converting from RGB to color index some information may be lost, three different conversion methods are available. To convert from monochrome to RGB first convert to color index format (vcmap) then convert to RGB (vccvt -i).

Command Function
vchan -c convert RGB image to monochrome
vcmap convert monochrome to color index (add cmap)
vccode convert RGB image to index format
vccvt convert RGB image to index format
vcdith convert RGB to a dithered fixed cmap index image
vccvt -i convert color index to RGB format
vxctable manage color-look-up tables

Color Tables
Color tables used in index images are provided for a number of different color schemes. In general, they specify 256 RGB colors that can be displayed with a color index image. In the v4/etc/ directory color tables in three different formats are maintained: (a) a binary format (.lut) which provide several standard visualization schemes, (b) a comma separated values (CSV) vtk format (.vkc) which provides for color labeling for images visualized by the vtk package, and label maps (.vlc) also encoded in CSV which provide mappings between image labels and specific colors. The commands listed above use the .lut format color tables while the commands listed below use the .vkc and vlc format color tables. The command vxctable will accept all color table formats and will provide a convenient visualization of their contents.

Image Region Visualization
True full color images (RGB) offer higher quality than color index images and are the preferred format for many image visualizations. A byte image used to host image regions (each region associated with a unique pixel value) is called a label map, a label definition file associates a set of label names with region pixel values. Finally, a label color map specifies a text label with a specifc RGB color. This system allows a user to use different coloring schemes for label maps.

For example, this is used for labeling anatomical regions (bones, lungs etc) in CT images of the chest. Different visualizations highlighting specific anatomical regions may be obtained by specifying different label color maps. The commands listed below support this scheme. vlmap manages label maps according to a specific label definitions file. vlctovkc converts a label color map to a vtk format (.vkc) for when a visualiztion is to be created with the vtk rendering package. vcmod modifies or modulates a color map with an intensity image.This is very useful for providing an image based visualization of an image segmentation.

Command Function
vlmap manage regions in a label map
vcmod modify a color region image with image intensities
vlctovkc VTK color file converter