Changing Color components

[logix1390]

I have a bit of an interesting problem which I thought was going to be easy

I have one of Houdini's pictures loaded in : Mandril.pic

I want to change only the red areas to whatever color I want. 

I know there is the hue shift and color correct nodes... but that will hue shift all the colors at the same time.

How do I only Hue shift the red channel to change it to whatever color i want???

vector to float >float to vector doesn't seem to work for this situation ...probably because Cd.x is not a vector...

This is driving me a little crazy... I will attach my scene file with my attempted methods.

Thank you

change_color_component.hipnc

[anim]

just approach it like comp

create mask from your channel and blend original and corrected color using that mask

change_color_component_fix.hipnc

[konstantin magnus]

In a point wrangle create an amount parameter (line 1) and convert the color values to HSV (line 2). Choose a range within the hue spectrum that is supposed to change (line 3). Multiply it by the amount and add the result to the hue component of the HSV color (line 4). Convert the color vector back to RGB (line 5).

float amount = chf('hue_shift');
vector col_hsv = rgbtohsv(v@Cd);
float range = chramp('mask_by_hue', col_hsv.x);
col_hsv.x += amount * range;
v@Cd = hsvtorgb(col_hsv);

change_color_component2.hipnc

Edited January 8, 2019 by konstantin magnus

[logix1390]

thanks guys, this works great