Colour Adjust Sliders

Started by ajcgi, February 21, 2018, 09:21:41 am

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ajcgi

The colour adjust shader has 2 pairs of sliders. When Black is black and white is white, both pairs mimic each other, but if a colour is set, they no longer do. This make us wonder... why? What does the bottom number here represent, numerically?

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luvsmuzik

For a beginner like me, it means when you put close to the full value of a color in either position, it changes the effect of what is being done. At full value black and white the effect is 1. Changing either color to clamp to changes that. Red is pretty close on the color wheel to full value black so your effect seems to be decreased significantly. Pink has quite a bit less effect than red in the end result. Are you using color adjust to stabilize, mix or mask with?

Matt

March 03, 2018, 12:52:53 am #2 Last Edit: March 03, 2018, 12:58:43 am by Matt
In this shader, the lower scalar value is the median of the RGB components. So if the RGB values are RGB(0, 0.1, 0.5)  the scalar value will be 0.1. This applies to white point, black point and gamma.

It's been about 16 years since I wrote this shader (can you believe it?!) but I think the reason it works this way is to allow you to shift the colours up or down without changing the spacing of the RGB values within the colour, and that can be helpful when dealing with negative black points. So let's take the example I gave earlier where the colour is RGB(0.0, 0.1, 0.5) and the median is 0.1. If you change the median to -0.4 all the values will be shifted by -0.5, so they become RGB(-0.5, -0.4, 0.0). This used to be a lot easier to see when the UI showed us all 3 RGB values (that changed before TG2 was released).

The number that's on the same line as the colour swatch works just like colours elsewhere in the program. It is the largest of the RGB components. But I wasn't satisfied with how that worked for black points.

Matt
Just because milk is white doesn't mean that clouds are made of milk.

ajcgi

Interesting. I think I understand that now. Cheers both!

Mid-Knight Acchan

There are two sliders in the gamma setting.
Contents of the saved .tgd file:
gamma = "0.4893650115 - 0.04717500135 0.000624999986"
gamma_adjust = "0.000625"
Are the two gamma settings different from each other?

Matt

'gamma_adjust' is the median of the 3 components of 'gamma'. In the GUI this allows you to shift the colour up or down without changing the spacing of the RGB values within the colour. It's a different way of adjusting the colour than the slider on the same line as the colour swatch. It's probably not very useful for gamma but it might be useful for the other colours in this shader.

Matt
Just because milk is white doesn't mean that clouds are made of milk.

Oshyan

We should probably have a label for that other setting though, in the UI... :D

- Oshyan

eapilot

I see this used in clouds a lot.  Is it used mostly like a levels node in other software to expand or clamp the range of a cloud density fractal or adjust the midpoint the midpoint values using the gamma slider?

D.A. Bentley

Read through this entire thread, and still don't understand.  Much of Terragen is cryptic like this to the "Artist" eyes, so I end up just experimenting until I get the desired result.

If this Color Adjust node is basically a Levels Adjust like in Photoshop, why can't we get a histogram added into the UI? 

Derek