[Nexus 5 Themes and Apps] mag01:
[MENTION=4809179]yorici[/MENTION]

I'll try describe it this way:

1. First approx 6 numbers cover highlights. Here I don't properly know how it works, but it seems that lower values make them brighter, but the effect is quite wide (wide range is affected)

2. Somewhere between the 6th-7th number you reach the middle of the range. Still decreasing values will make colors brighter.

3. 12th value (just before the red peak, for green and blue it's the peak) is the last one where decreasing the value will make things brighter

4. 13th value (red peak, just after the green and blue peak) is the first one where things start behaving the opposite way. Lower value will make colors darker.

5. By the end of the series you reach the darkest area. Here still lower values make colors darker.

Some notes:

- Highlights are tricky, they're covered by just approx 6 values out of those 23 and changing any of them has quite wide effect (on the whole highlights range). Also the effect doesn't seem to be that strong compared to shadows.

- Try to change first blue value (86) to 0 and see the gradients in display tester: Banding, contrast, saturation; 1st and 2nd screens

- That will also show you what I meant by speculating about two processing paths (highlights vs shadows) because you'll see a sharp transition in hte middle of the range.

- Modifying any value inappropriately (not respecting the curve shapes) will cause big distortions in the nearby area. The effect is like the graph B here: http://www2.engr.arizona.edu/~ocpl/images/new/optim_pump_profile.jpg - that means you need to be very careful when doing any changes. Altering just few values just to achieve the desired gamma without understanding what those changes actually do isn't good approach and you'll likely end up with distorted colors somewhere in the range. Gamma isn't the only thing to look at.

- Modifying positives and negatives separately has similar effect. When you modify them both (that's probably better than modify them separately), the effect is cumulative (stronger). There's also some slight offset between positive and negative, for example for red color the negative value affects the colors slightly more on the highlights side of the range.

- In any case if you go too far off with modifications, there will be lots of negative effects visible. Various banding effects, strange lines appearing out of nowhere etc.

Funny thing related to the change in the behavior between 12-13th values:

Change 13th: +5 - results in bright bar with another dark bars on both sides (distortions).

Now to compensate for that you'd normally expect to increase for example the 12th value by approx +5 as well... Wrong, you have to decrease it instead, e.g. : -5 :D

So you start with 12: 100, 13: 100, change it to 12:100, 13: 105 and then to fix the distortion you have to end up with something like 12:95, 13:105 instead of 12: 105, 13:105 (what one would normally expect) :D

As for cyan, you'd need a wide gamut display to get better results as cyan is one of weak spots of ordinary (standard gamut) displays. Have a look at this for example: http://a.img-dpreview.com/reviews/NikonD100/Samples/ColorMode/chromaticity_diagram_gamut.jpg ordinary displays are somewhere near the sRGB coverage.

EDIT: As for the white point, it's normal what you describe. See here for example http://xdaforums.com/showpost.php?p=27815564&postcount=1581 - white point moves on the curve in the middle of the diagram. as for several local maximum points - it probably just goes back to the middle, perhaps by following slightly different curve. You'd need a spectrophotometer to find out.