unexpected behaviour in LAB mode.

[Xzenor]

Hi, so I ran into something I didn't expect.

Ever since I discovered that you can adjust luminosity without changing the color in LAB mode, I've been in love with it. Today though I ran into a weird thing.

For small Dodging and Burning changes I like to make a 50% gray layer, set blending mode to overlay or soft light and then D&B on that layer. Works like a charm, in RGB.

However, in LAB mode the 50% gray layer in overlay or soft light visibly increases the luminosity of the entire picture. Why is that?

I know I can use 2 curves layers for D&B but that's not the point here. I'm trying to understand why this works differently in LAB than in RGB. Does anyone here know why this happens?

[lepr]

Your RGB 50% grey or Grey 50% doesn't convert to LAB (50,0,0). The Colour panel can be set to LAB mode where you can specify LAB (50,0,0) for the grey layer.

[Xzenor]

omg.. I never even noticed that option..

I never imagined it would be this.

But why is there a difference? 50% gray is 50% gray. if the scale is -100 to +100 or -500 to +500, the middle is still zero. What's happening?