Recolour Adjustment - HEX code/RGB/HSL/CMYK etc?

HydroJLW · March 23, 2023

Hi,

I recently noticed when using the recolour adjustment, it gives you the colours on a degree scale with saturation and lightness options underneath.

Everything else in the app works with HEX codes or RGB/HSL/CMYK etc sliders. Is there a reason for this? It seems to make recolouring to a set value, very difficult. Does anyone know if you can set a recolour adjustment to a HEX value (or other RGB/HSL etc) or how the degree scale translates to these other formats?

Thank you

NotMyFault · March 23, 2023

Recolor offers input for hue and saturation as absolute values in the scale 0-360 for hue, and 0-100 for saturation.
lightness is taken from source image. The slider allows relative adjustment +/- 100%

Hex values are mostly used for absolute RGB, which does not make sense here

hex values are 00-FF, equals 0-255 in decimal. You normalize to float 0.0 -1.0 by dividing by 255.

You would need to convert RGB into HSL, take H and S, ignore L

multiply H by 360

multiply S by 100

see https://en.wikipedia.org/wiki/HSL_and_HSV

From RGB[edit]

See also: § General approach

This is a reiteration of the previous conversion.

Value must be in range $R,G,B\in [0,1]$ .

With maximum component (i. e. value)

$X_{max}:=\max(R,G,B)=:V$

and minimum component

$X_{min}:=\min(R,G,B)=V-C$ ,

range (i. e. chroma)

$C:=X_{max}-X_{min}=2(V-L)$

and mid-range (i. e. lightness)

$L:=\operatorname {mid} (R,G,B)={\frac {X_{max}+X_{min}}{2}}=V-{\frac {C}{2}}$ ,

we get common hue:

$H:={\begin{cases}0,&{\text{if }}C=0\\60^{\circ }\cdot \left({\frac {G-B}{C}}\mod 6\right),&{\text{if }}V=R\\60^{\circ }\cdot \left({\frac {B-R}{C}}+2\right),&{\text{if }}V=G\\60^{\circ }\cdot \left({\frac {R-G}{C}}+4\right),&{\text{if }}V=B\end{cases}}$

and distinct saturations:

$S_{V}:={\begin{cases}0,&{\text{if }}V=0\\{\frac {C}{V}},&{\text{otherwise}}\end{cases}}$

$S_{L}:={\begin{cases}0,&{\text{if }}L=0{\text{ or }}L=1\\{\frac {C}{1-\left\vert 2V-C-1\right\vert }}={\frac {2(V-L)}{1-\left\vert 2L-1\right\vert }}={\frac {V-L}{\min(L,1-L)}},&{\text{otherwise}}\end{cases}}$

i made a conversion by procedural texture filters, see

HydroJLW · March 23, 2023

35 minutes ago, NotMyFault said:

Wow - thank you for this, I'll have a read.

I feel like HSL recolour options could be a useful feature...and probably easily added I would have though.

Cheers

Recolor offers input for hue and saturation as absolute values in the scale 0-360 for hue, and 0-100 for saturation.
lightness is taken from source image. The slider allows relative adjustment +/- 100%

Hex values are mostly used for absolute RGB, which does not make sense here

hex values are 00-FF, equals 0-255 in decimal. You normalize to float 0.0 -1.0 by dividing by 255.

You would need to convert RGB into HSL, take H and S, ignore L

multiply H by 360

multiply S by 100

see https://en.wikipedia.org/wiki/HSL_and_HSV

From RGB[edit]

See also: § General approach

This is a reiteration of the previous conversion.

Value must be in range $R,G,B\in [0,1]$ .

With maximum component (i. e. value)

$X_{max}:=\max(R,G,B)=:V$

and minimum component

$X_{min}:=\min(R,G,B)=V-C$ ,

range (i. e. chroma)

$C:=X_{max}-X_{min}=2(V-L)$

and mid-range (i. e. lightness)

$L:=\operatorname {mid} (R,G,B)={\frac {X_{max}+X_{min}}{2}}=V-{\frac {C}{2}}$ ,

we get common hue:

$H:={\begin{cases}0,&{\text{if }}C=0\\60^{\circ }\cdot \left({\frac {G-B}{C}}\mod 6\right),&{\text{if }}V=R\\60^{\circ }\cdot \left({\frac {B-R}{C}}+2\right),&{\text{if }}V=G\\60^{\circ }\cdot \left({\frac {R-G}{C}}+4\right),&{\text{if }}V=B\end{cases}}$

and distinct saturations:

$S_{V}:={\begin{cases}0,&{\text{if }}V=0\\{\frac {C}{V}},&{\text{otherwise}}\end{cases}}$

$S_{L}:={\begin{cases}0,&{\text{if }}L=0{\text{ or }}L=1\\{\frac {C}{1-\left\vert 2V-C-1\right\vert }}={\frac {2(V-L)}{1-\left\vert 2L-1\right\vert }}={\frac {V-L}{\min(L,1-L)}},&{\text{otherwise}}\end{cases}}$

i made a conversion by procedural texture filters, see

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Recolour Adjustment - HEX code/RGB/HSL/CMYK etc?

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