IMAGING GLOSSARYLook-Up-Table (computer hardware)A look-up-table or LUT is a continuous block of computer memory that computes the values of a function for one variable.
The LUT is set up for the function's variable to be used as an address or offset into the memory block. The value that resides at this memory location becomes the function's output.
Because the LUT values need only be initialized once, LUTs are very useful for image processing due to their inherent high speed.
LUT[pixel_value] = f(pixel_value)
LUTs come in various widths, usually in units of bits. An nxm bit LUT has 2n addresses or 256 stored values. Each value is 2m bits wide.
If the second dimension is left off it can be assumed to be equal to the first.
In gray-scale image processing, LUTs are commonly 8x8, and the bit widths are usually assumed.
A linear LUT, sometimes called a NOP LUT or pass through, is a LUT that is initialized to output the same values as the input. NOP_LUT[pixel_value] = pixel_value.
See palette (digital imaging).
Back to Imaging Glossary IndexImaging Categories: | 
