Lookup Table (LUT)
A lookup table (LUT) in
computer graphics is an array or data structure that maps input values
(such as pixel intensities) to new output values (colors or brightness) to
replace complex, slow computations with fast memory access. They are primarily
used for color calibration, color grading, and optimizing image processing by
precomputing results.
A Lookup Table (LUT) is a table that stores
actual colors.
- Each
index (0–255) maps to a specific RGB value
- Each
RGB color uses:
- Red
→ 8 bits
- Green
→ 8 bits
- Blue
→ 8 bits
👉 Total = 24 bits per color
Image representation is
essentially the description of pixel colors. There are three primary colors: R
(red), G (green) and B (blue). Each primary color can take on intensity levels
produces a variety of colors. Using direct coding, we may allocate 3 bits for
each pixel, with one bit for each primary color. The 3-bit representation
allows each primary to vary independently between two intensity levels: 0 (off)
or 1 (on). Hence each pixel can take on one of the eight colors.
🔹 Advantages
- ✅ Saves memory
(8-bit vs 24-bit)
- ✅ Faster
processing
- ✅ Useful for
images with limited colors (icons, GIFs)
🔹 Disadvantages
- ❌ Limited to 256
colors at a time
- ❌ Not suitable
for high-quality photos (color loss)
What is Indexed Color?
Indexed color is a
technique used in computer graphics to reduce memory usage of images.
- Instead
of storing full color for each pixel (like RGB),
we store a small number (index) for each pixel. - Typically
uses 8 bits per pixel → 256 possible values (0–255)
👉 Each value is not a color itself —
it is an index pointing to a color.
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