rgb2ansi256

rgb2ansi256 is a small Rust library to convert RGB 24-bit colors into ANSI 256 (8-bit) color codes with zero dependencies and const fn. This crate was ported from ansi_colours C library v1.0.4.

By porting the library, we have the following two benefits:

• No unsafety
• Compile time calculation (no runtime overhead)

use rgb2ansi256::rgb_to_ansi256;

const MEDIUM_SPRING_GREEN: u8 = rgb_to_ansi256(0, 255, 175);

assert_eq!(MEDIUM_SPRING_GREEN, 49);

The documentation

Here is a comparison before/after conversion.

The left window is iTerm2 which supports 24-bit colors (true colors). The right window is Terminal.app which supports only 8-bit colors. Conversion could reproduce 24-bit colors in 8-bit colors well.

Installation

Add this crate to your Cargo.toml.

[dependencies]
rgb2ansi = "0.1"

Benchmark

This is the result of the micro benchmark suite. rgb2ansi256 is slightly faster than ansi_colours.

rgb2ansi256             time:   [150.58 us 151.06 us 151.55 us]
                        change: [-1.2657% -0.9774% -0.6991%] (p = 0.00 < 0.05)
                        Change within noise threshold.
Found 9 outliers among 100 measurements (9.00%)
  5 (5.00%) low mild
  4 (4.00%) high mild

ansi_colours            time:   [158.07 us 158.83 us 159.64 us]
                        change: [-1.3717% -0.7338% -0.1909%] (p = 0.02 < 0.05)
                        Change within noise threshold.
Found 12 outliers among 100 measurements (12.00%)
  3 (3.00%) low mild
  8 (8.00%) high mild
  1 (1.00%) high severe

• Machine: iMac (Retina 5K, 27-inch, 2020)
• ansi_colours: v1.0.4
• rustc: 1.56 (stable)

License

Inheriting from the original C library, this library is distributed under LGPL-3.0 License.