treeform / chroma Goto Github PK

The Oklab->RGB transform is currently broken: in the last matrix multiplication it uses the LMS components instead of the LMS^3 ones it calculates just above.

Minimal reproducible example:

import std/strutils, chroma

proc `$`(c: ColorRGB): string = "#" & c.r.toHex(2) & c.g.toHex(2) & c.b.toHex(2)
proc `$`(c: ColorOklab): string = $c.asRgb

let c = ColorRGB(r: 0, g: 255, b: 0)
echo c, c.asOklab

Expected output: #00FF00#00FF00
Actual output: #00FF00#8D0A7F

hii!

i'm struggling to use this library for some image processing and palette mapping tasks. I've found that transforming to oklab and back significantly brightens and desaturates colors.

import chroma
echo parseHex("F8DB57").to(ColorOklab).to(ColorRGB).color.toHex()
# output:      FCF4BA

Color #F8DB57 turns into #FCF4BA.

Here's some assorted roundtrips:

import chroma
import random
import strformat

proc chip(c: ColorRGB): string =
    ## nice-looking color chip for github-flavored markdown
    let hex = c.color.toHex()
    fmt"`#{hex}` <img valign='middle' alt='blue' src='https://readme-swatches.vercel.app/{hex}'/>"

randomize()
for _ in 1..10:
    let color = ColorRGB(
        r: random.rand(255).uint8,
        g: random.rand(255).uint8,
        b: random.rand(255).uint8,
    )
    let color2 = color.to(ColorOklab).to(ColorRGB)
    echo fmt"{color.chip} -> {color2.chip}"

Output:

#FF1580 -> #1A89CC
#B543B5 -> #E9A8E6
#DBCA21 -> #F1EF99
#28B837 -> #9CE9A0
#E254E2 -> #FBB5F8
#5103BC -> #B06BF8
#3F51B2 -> #A0B0E7
#DB26C5 -> #0196EF
#B44D3E -> #EAAEA1
#803A22 -> #D09E86

Each pair of colors should be identical (before converting to OkLab and after). But for many of these pairs, even the hue is wildly off.

With the doc updates, the additions of the other color spaces and especially the Nim 1.0 release I think it'd be a good idea to release a new version of chroma, so that nimble install gives a reasonably new package.

hey, first of all I appreciate your work for Nim community. you made dozens of useful libraries.

i have a sample image named sample.png: [the background is transparent]

here's my code:

import pixie, chroma

var img = readImage("./sample.png")

func reverse(clr: Color, reverseAlpha = false): Color=
  Color(
    r: 255 - clr.r,
    g: 255 - clr.g, 
    b: 255 - clr.b,
    a: if reverseAlpha: 1 - clr.a else: clr.a)

for i in 0..<img.data.len:
  template clr: untyped = img.data[i]
  # clr = clr.asColor.spin(0).asRgbx # 1
  # clr = clr.asColor.reverse.asRgbx # 2
  # clr = clr.asColor.reverse.spin(0).asRgbx # 3

img.writeFile("./res.png")

1. if I comment out the first commented line [#1] I get the same image: [which is obviously correct - it spins the colors 0 degrees]

2. if I comment out [#2] i get this: [which is correct]
   

3. however, if i comment out [#3] i get this: [which is strange]:
   

I'm really not sure if it's a bug or not, please tell me if I did anything wrong

Hi there Treeform,

You probably know about this one already, but in case you don't: https://bottosson.github.io/posts/oklab/

I'm using this package in clr and would appreciate having a tagged release I could specify in my .nimble file (preferably following Semantic Versioning). I'm currently pinning a commit hash there, but it's better to rely on commits which are known to be stable and compatible 🙂

Support for grey / grayscale uint8, 16, 32, float 32 [0, 1] & alpha

transformations, conversion to: greyscale
equal weight 1/3 * r + 1/3 * g + 1/3 * b
ITU-R BT.709 (HDTV) 0.21 * r + 0.72 * g + 0.07 * b
ITU-R BT.601 (PAL) 0.299 * r + 0.587 * g + 0.114 * b
user defined weight

ITU-R BT.709 (HDTV) as default(?)

convenience operator:
let value = color(0.5,0.5,0.1).gray

in the hope it will trickle into Pixie

This is the root cause of #41.

Running nimble install chroma gets commit b2e7117, which is two years old.

$ nimble install chroma
Downloading https://github.com/treeform/chroma using git
  Verifying dependencies for [email protected]
 Installing [email protected]
  Success:  chroma installed successfully.
$ cat ~/.nimble/pkgs2/chroma-0.2.7-f873f4b97e87a82e27e0b85bf9130fe3e320a2b8/nimblemeta.json
{
  "version": 1,
  "metaData": {
    "url": "https://github.com/treeform/chroma",
    "downloadMethod": "git",
    "vcsRevision": "b2e71179174e040884ebf6a16cbac711c84620b9",
    "files": [
      "/chroma/distance.nim",
      "/chroma/csstint.nim",
      "/chroma/transformations.nim",
      "/chroma/colortypes.nim",
      "/chroma.nim",
      "/chroma/blends.nim",
      "/chroma/temperature.nim",
      "/chroma.nimble",
      "/chroma/names.nim"
    ],
    "binaries": [],
    "specialVersions": [
      "0.2.7"
    ]
  }
}

Title says it all. When running nim js bars.nim I get the following error:

/Users/jamen/.nimble/pkgs/chroma-0.1.1/chroma/distance.nim(10, 32)
/usr/local/Cellar/nim/1.2.6/nim/lib/pure/math.nim(1014, 16) ^
/usr/local/Cellar/nim/1.2.6/nim/lib/system/arithmetics.nim(499, 9) *=
/usr/local/Cellar/nim/1.2.6/nim/lib/system/arithmetics.nim(499, 9) Error: unhandled exception: value out of range

I confirmed that this error does not occur on chroma-0.1.0 (there is no distance.nim). This seems to be specific to macOS since Nim Playground doesn't reproduce this issue.