This PR attempts to close #5.

Here's some output using the three accepted arguments for --output with the lighthouse.

#e9e4d7
#858b88
#4576bb
#2c231b
#c53b4e

rgb(233, 228, 215)
rgb(133, 139, 136)
rgb(69, 118, 187)
rgb(44, 35, 27)
rgb(197, 59, 78)

rgb(0.914, 0.894, 0.843)
rgb(0.522, 0.545, 0.533)
rgb(0.271, 0.463, 0.733)
rgb(0.173, 0.137, 0.106)
rgb(0.773, 0.231, 0.306)

rgb01 formats the floats so that there is always 3 digits after the decimal. 3-digits after the decimal was chosen because 1 / 255 is roughly 0.004, so 2 digits would lose some precision. A side effect of this is that you always get 3-digits after the decimal, so a channel at its maximum will print "1.000" which I'm not sure is desirable behavior. It's quite verbose.

Something like:

--output=(hex | rgb255 | rgb01)

where hex is the default, rgb255 gives you an RGB tuple with integer values (0–255) and rgb01 gives you an RGB tuple with float values (0-1).

Plus bump the version of the image crate.

I looked at bumping the version of palette, but then I get issues with the kmeans_colors crate and I can't be bothered to deal with that today.

This flag should return a single colour, filtering for a 4.5:1 contrast ratio and then maxing for saturation. Essentially replicating the logic from docstore: https://github.com/alexwlchan/docstore/blob/main/src/docstore/tint_colors.py

👋🏾 hello Alex! I was working on adding tests for #5 (PR incoming) and I noticed that the test for --no-palette was the same as the test without it. Seems like a copy paste error. I think this test is correct now, it passes!

Also I really like how you structure and name your tests. Tests have been something I am not-so-good-at and I am definitely going to try and mimic the way you do them. I didn't know there was a way to call the binary cargo outputs either! That's very nice.

$ ./target/debug/dominant_colours ./README.md
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: Unsupported(UnsupportedError { format: PathExtension("md"), kind: Format(PathExtension("md")) })', src/main.rs:60:34
stack backtrace:
   0: rust_begin_unwind
             at /rustc/a178d0322ce20e33eac124758e837cbd80a6f633/library/std/src/panicking.rs:515:5
   1: core::panicking::panic_fmt
             at /rustc/a178d0322ce20e33eac124758e837cbd80a6f633/library/core/src/panicking.rs:92:14
   2: core::result::unwrap_failed
             at /rustc/a178d0322ce20e33eac124758e837cbd80a6f633/library/core/src/result.rs:1355:5
   3: core::result::Result<T,E>::unwrap
             at /rustc/a178d0322ce20e33eac124758e837cbd80a6f633/library/core/src/result.rs:1037:23
   4: dominant_colours::main
             at ./src/main.rs:60:15
   5: core::ops::function::FnOnce::call_once
             at /rustc/a178d0322ce20e33eac124758e837cbd80a6f633/library/core/src/ops/function.rs:227:5
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

$ ./target/debug/dominant_colours ./holepunch-clouds.tiff
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: Unsupported(UnsupportedError { format: Exact(Tiff), kind: Format(Exact(Tiff)) })', src/main.rs:60:34
stack backtrace:
   0: rust_begin_unwind
             at /rustc/a178d0322ce20e33eac124758e837cbd80a6f633/library/std/src/panicking.rs:515:5
   1: core::panicking::panic_fmt
             at /rustc/a178d0322ce20e33eac124758e837cbd80a6f633/library/core/src/panicking.rs:92:14
   2: core::result::unwrap_failed
             at /rustc/a178d0322ce20e33eac124758e837cbd80a6f633/library/core/src/result.rs:1355:5
   3: core::result::Result<T,E>::unwrap
             at /rustc/a178d0322ce20e33eac124758e837cbd80a6f633/library/core/src/result.rs:1037:23
   4: dominant_colours::main
             at ./src/main.rs:60:15
   5: core::ops::function::FnOnce::call_once
             at /rustc/a178d0322ce20e33eac124758e837cbd80a6f633/library/core/src/ops/function.rs:227:5
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

Currently:

$ ./target/debug/dominant_colours  ./doesnotexist.jpg
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: IoError(Os { code: 2, kind: NotFound, message: "No such file or directory" })', src/main.rs:60:34
stack backtrace:
   0: rust_begin_unwind
             at /rustc/a178d0322ce20e33eac124758e837cbd80a6f633/library/std/src/panicking.rs:515:5
   1: core::panicking::panic_fmt
             at /rustc/a178d0322ce20e33eac124758e837cbd80a6f633/library/core/src/panicking.rs:92:14
   2: core::result::unwrap_failed
             at /rustc/a178d0322ce20e33eac124758e837cbd80a6f633/library/core/src/result.rs:1355:5
   3: core::result::Result<T,E>::unwrap
             at /rustc/a178d0322ce20e33eac124758e837cbd80a6f633/library/core/src/result.rs:1037:23
   4: dominant_colours::main
             at ./src/main.rs:60:15
   5: core::ops::function::FnOnce::call_once
             at /rustc/a178d0322ce20e33eac124758e837cbd80a6f633/library/core/src/ops/function.rs:227:5
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.