Per-pixel intensity mapping for display colors, tone curves and more
A display LUT is an array of 256 (or 2N) entries, each holding an RGB triplet. Each pixel's intensity indexes the array and returns that pixel's display color. Linear LUTs map proportionally (green: 0→black, 255→bright green). Non-linear LUTs such as 'Fire' use multi-segment color ramps to enhance contrast in particular intensity ranges.
A display LUT does not modify the stored pixel values. Quantitative measurements are always made on the raw intensity data, never on the false-color display.
LUTs serve two purposes. In a multi-channel composite they assign each channel its identity (green for GFP, red for mCherry). They can also enhance visual contrast, revealing features that are hard to see in plain grayscale. Choosing a display LUT is a presentation decision, and it must never be confused with changing the data.
A four-channel multiplex image uses four LUTs: DAPI nuclei in blue, CD3 T cells in green, PD-L1 in red and Ki-67 proliferation in cyan. Each channel is a separate grayscale image, and the LUTs build the false-color composite. The same raw data could be displayed with entirely different LUT assignments.
