HCG color model support

I looked to code - too hard...
I beg to help implement HCG color model for your library.
https://github.com/acterhd/hcg-color

[dmilos]

Hello
Thank you for interest for color library.

Adding new model I not so trivial.
Here is possible steps:

• create HCG folder
• copy all files from CMY ( or CMYK, do not use RGB )
• search/replace CMY with HCG.
• Search every place that CMY appear and add HCG. This is tricky.
  -- You have to do the same with files too. Very tricky.
• implement conversion RGB<->HCG
• in example/test folder add testing of HCG, gray, conversion, etc.
  -- generate ::color::make functions and test and test and test and test and
  test ...

... and I guess that is all.

On github Implementation looks simple but there some heavy JS language
usage.
If you can point me to some c implementation I can easily do this for you.
I'll also make branch for HCG

I found this is https://phabricator.kde.org/D1374#10659608

Regards
Dejan

On Mon, Aug 22, 2016 at 4:14 AM, acterhd notifications@github.com wrote:

I looked to code - too hard...
I beg to help implement HCG color model for your library.
https://github.com/acterhd/hcg-color

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[dmilos]

I use use both.

On Mon, Aug 22, 2016 at 9:38 PM, acterhd notifications@github.com wrote:

You using GCC? No Visual Studio?

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[dmilos]

Most important part is conversion RGB<-> HCG.
Everything else is support of that.
I already set that support. See branch HCG.
All I need is RGB<-> HCG.
JS I pretty hazy to me.|
Can you convert to simple c?

On Mon, Aug 22, 2016 at 9:54 PM, acterhd notifications@github.com wrote:

Bad news... I lost formulas for convert HCG/HSV and HCG/HSL. I used
special converter in death-color (destroy to min/max/chroma and recompiling
color model).

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[dmilos]

Perfect.
Thanks.

On Mon, Aug 22, 2016 at 10:54 PM, acterhd notifications@github.com wrote:

typedef struct {
double r;
double g;
double b;
} rgb;
typedef struct {
double h;
double c;
double g;
} hcg;
static hcg rgb2hcg(rgb in);static rgb hcg2rgb(hcg in);

hcg rgb2hcg(rgb in)
{
hcg out;
double min, max, delta;

min = in.r < in.g ? in.r : in.g;
min = min  < in.b ? min : in.b;

max = in.r > in.g ? in.r : in.g;
max = max  > in.b ? max : in.b;

delta = max - min;
out.c = delta;
if (delta < 0.00001)
{
    out.h = 0;
    out.c = 0.0;
    out.g = min;
    return out;
}
if (delta < 1.0) {
    out.g = min / (1.0 - delta);
}

if (in.r >= max)
    out.h = (in.g - in.b) / delta;
else
if (in.g >= max)
    out.h = 2.0 + (in.b - in.r) / delta;
else
    out.h = 4.0 + (in.r - in.g) / delta;

out.h *= 60.0;

if (out.h < 0.0)
    out.h += 360.0;

return out;

}

rgb hcg2rgb(hcg in)
{
double hh, p, q, t, ff, v;
long i;
rgb out;

if (in.c <= 0.0) {       // < is bogus, just shuts up warnings
    out.r = in.g;
    out.g = in.g;
    out.b = in.g;
    return out;
}
hh = in.h;
if (hh >= 360.0) hh = 0.0;
hh /= 60.0;
i = (long)hh;
ff = hh - i;
p = in.g * (1.0 - in.c);
q = p + in.c * (1.0 - ff);
t = p + in.c * ff;
v = p + in.c;

switch (i) {
case 0:
    out.r = v;
    out.g = t;
    out.b = p;
    break;
case 1:
    out.r = q;
    out.g = v;
    out.b = p;
    break;
case 2:
    out.r = p;
    out.g = v;
    out.b = t;
    break;
case 3:
    out.r = p;
    out.g = q;
    out.b = v;
    break;
case 4:
    out.r = t;
    out.g = p;
    out.b = v;
    break;
case 5:
default:
    out.r = v;
    out.g = p;
    out.b = q;
    break;
}
return out;

}

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[dmilos]

What if someone want more precision than two/three numbers?

On Tue, Aug 23, 2016 at 8:07 PM, acterhd notifications@github.com wrote:

Something wrong.
color::hcg hcgi({ 0.0, 50.0, 100.0 });
I can't use doubles :(

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[dmilos]

For example some image processing, no alpha channel.
If you try to find average image pre-converted sequence in HCG you will have huge numerical error.

Full HSX converter, nearly all from worlds!
https://github.com/acterhd/death-color/blob/master/convert/index.js

[dmilos]

Thanks.
I'll take a look.

On Sat, Sep 10, 2016 at 4:25 PM, acterhd notifications@github.com wrote:

Full HSX converter, nearly all from worlds!
https://github.com/acterhd/death-color/blob/master/convert/index.js

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Will support more color models?