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Disparity in Numerical RGB Coordinates in Log Mode when using Mouse Versus Trackball

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Desmond Ford
Disparity in Numerical RGB Coordinates in Log Mode when using Mouse Versus Trackball
on May 9, 2013 at 5:53:43 pm

I'm experiencing something odd in Log mode when I use the mouse to make RGB adjustments versus when I use the trackballs of my Tangent Element.

Basically, I'll make the same adjustment with the mouse as I will with the trackball, but the numerical RGB coordinates are way off.

For example, I'll use my mouse to move the little circle inside the highlight wheel so that it rests in the corner of the crosshairs of the Magenta vector. The coordinates will read R: 0.16 / G: -0.07 / B: 0.20

Then I'll reset it and make the exact same move with my trackball to the same (almost exact by eye) location as before. However, the coordinates read completely differentR: 0.04 / G: -0.18 / B: 0.10

Further, there is a stark difference in the numerical coordinate values. Yet the relative position is almost identical in the Highlight Wheel of the Log mode. It looks noticeably different too.

I know what you're thinking: it's impossible to match it up exactly by eye!

So what I do is, I take a frame grab of both adjustments, then I toggle back and forth while looking at the little circle in the highlight wheel, and I can see no movement. It looks to my eye that the little circle has not moved position at all, despite the RGB coordinates below changing back and forth to extremely different values and the image showing a difference via the wipe.

I called tech support but they were unable to make anything of it from my description, so I'm posting it here with screengrabs for clarification.







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Toby Tomkins
Re: Disparity in Numerical RGB Coordinates in Log Mode when using Mouse Versus Trackball
on May 9, 2013 at 6:22:27 pm

Maybe it's related to your control panel sensitivity?


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Desmond Ford
Re: Disparity in Numerical RGB Coordinates in Log Mode when using Mouse Versus Trackball
on May 9, 2013 at 7:21:51 pm

I considered that and even discussed it with tech support, but the trackball sensitivities only affect speed, not position.

The point itself should be uniform whether I arrive via trackball, mouse or pen tablet.


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Dwaine Maggart
Re: Disparity in Numerical RGB Coordinates in Log Mode when using Mouse Versus Trackball
on May 9, 2013 at 8:01:39 pm

Here's what seems to be happening, though I don't know why.

When you adjust the trackball indicator with the mouse, it appears to be also changing the master gain. If you make a panel adjustment and save it in a mem, then make a mouse adjustment to put the indicator in the same place and save a mem, then lower the Master wheel on the GUI, you can get the same values with the indicator at the same point, as you do with the panel.

I thought this might be related to the Lum Mix setting, but it's not.

Perhaps someone on the development team can comment.

Dwaine Maggart
Blackmagic Design DaVinci Support


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Joseph Owens
Re: Disparity in Numerical RGB Coordinates in Log Mode when using Mouse Versus Trackball
on May 10, 2013 at 4:03:31 pm

[Dwaine Maggart] "I thought this might be related to the Lum Mix setting, but it's not. "

Perhaps it is a nod in the right direction. My mental model of how the original daVinci (not Resolve) RGB correction system worked was that it was always trying to maintain "constant luminance" while you were adjusting color balance. Of course, you have to re-adjust all the other factors to maintain the derived "Y'" value while tweaking the RGB, so i cannot see how else that could be numerically achieved. So saying, the "RGB" that achieves a certain Y'CbCr may not be the same RGB you think you were dialling in.

Personally, I don't pay any attention at all to the three-way thingies. How the desired values are achieved, or for some reason transferable in various modes, is irrelevant to the end result. The only time it might become important would be to indicate that I've run out of juice, and "11" is not achievable.

jPo

"I always pass on free advice -- its never of any use to me" Oscar Wilde.


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Margus Voll
Re: Disparity in Numerical RGB Coordinates in Log Mode when using Mouse Versus Trackball
on May 12, 2013 at 6:16:40 am

So in some sense this confirms that on panels one gets more precise adjustments.

I have had this "feeling" a long time but have not investigated it in detail.

--

Margus

http://iconstudios.eu
https://vimeo.com/iconstudioseu/videos

DaVinci 9, OSX 10.7.4
MacPro 5.1 2x2,93 24GB
GTX 470 / Quadro 4000
Multibridge 2 Pro


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