Blackmagic Forum

Hi, I'm very confused by 'Lum Mix' - I have this on my Mini Panel and I must confess I have no idea what it does. I've searched on this forum and on google but I can't find an explanation. Can anyone help?

By the way I have read the explanation for this in the manual (I would post it here except I can't seem to copy text from the manual pdf) and I can't really understand the manual explanation, so hoping someone might be able to offer a simpler explanation!

Perhaps I should mention, I also struggle with y-lift, y-gamma and y-gain and how this differs from just adjusting the lift, gamma and gain on the wheels. I believe the Lum mix is associated with these controls. I have a pretty good understanding of resolve otherwise, but I'm just struggling to get my head around this...

By default, Resolve will manipulate the color channels together even if you're doing something to only one channel, to maintain the levels of the image. This is more intuitive to us, but is accomplished through complicated math. Setting Lum Mix to 0 changes this behavior.

On the topic of Y, check out this thread: viewtopic.php?f=21&t=78837

Many thanks for the link, I had a quick scan through and I think the point one person made that RGB contains all the information so what is Y for was kind of similar to where I'm at right now. I think I'll need to have a proper read through to really get my head around it! I just can't think of a practical situation where I'd need to use Y-lift, Y-gamma, Y-gain or Lum Mix over just using lift, gamma and gain? Would you be able to give an example where any of these might be useful? Thanks again,

So, to really understand what the Lum Mix does, you’ll have have a at least pretty good understanding of color science. If I were to explain it in a simpler way, it would be something like this:

In every color space, each primary (R, G and B channels) does not contribute equally to the luminance (the perceived intensity or brightness of the image). For example, in REC 709, red contribute about 21%, green about 72% and blue about 7% to the total luminance of the image. So, let’s say that we want to color correct a image by reducing the green by 50% and increase the blue with 50%. Since the total contribution of the green and blue channels to luminance are different, the image will be perceived as darker after the adjustment. What the Lum Mix is doing is automatically compensating the values you put in to Resolve, and thus tries to maintain the same luminance all the time, independently of how the color change. If you turn of the Lum Mix (by setting it to 0), you can see what the result would be by just adjusting the R, G and B levels without compensating for the luminance.

In most cases you would leave the Lum Mix on, just because the color adjustments will just feel more intuitive. But using the Y controls can be used creatively, for example to create a silver retain type effect. This can be done by fist reducing the contrast of a image by increasing lift and lowering gain, and then increase the contrast again to the original black and white levels by decreasing Y-lift and increasing Y-gain.

I hope this helps.

The best explanation I can give for Lum Mix would be for you to try it. Leave it up at 100. Now take the Y Gain channel (shown in the Primary Bars display), and drop it to 100. The image should be totally black. Undo that, and change Lum Mix to 0. Drop the Y Gain down to 100, and what you'll see is the luminance values have disappeared, leaving only the chroma portions of the image. Watch the scopes and you'll immediately see what's happening. Page 1948 of the Resolve 15 manual covers the basics.

The RGB Mixer has a similar mode, "Preserve Luminance," where if you turn that on, you can adjust Red-only, Green-only, or Blue-only without the system compensating for luminance levels. There are situations where this is useful.

I agree with Oyvind above that most of the time, leaving Lum Mix set to 100 makes more sense. But there are special occasions where you need to bypass it. I wouldn't suggest doing it unless you're extremely aware of what it's doing.