Lab color yellow L=100?

[P38942367gj62]

Making my own simple Lab color wheel.

all colors on the middle gray plain L=50,

red, blue, green all work fine

"yellow" on the mid gray plain is brown

it works if I crank it up to L=100.

is this an old fudge to get Lab color on a computer screen?

[davescm]

That diagram is theoretical. As described above, a visible lit colour is restricted within that theoretical space, and a colour represented using three (RGB) primaries, as you see on a screen, even more so. 

Dave

[P38942367gj62]

That could be.

photoshop is using the wrong crayons.

RGB has the lightness baked in

Lab keeps the "colors" and grayscale separate.

photoshop can create a pure yellow

just not a Lab pure yellow

which should lie on the middle gray color plane,

theoretically, I guess,

I like, as designed,

not reproducable in RGB color space,

better.

[davescm]

'photoshop is using the wrong crayons'

Any imaging software, in RGB mode is using Red Green and Blue primaries based on the colour space and an additive process to mix those three. This introduces restrictions. CMYK mode has other restrictions, Lab mode takes away certain restrictions but....

Even though those RGB document restrictions could be overcome in theory, the display of the results on a monitor are still restricted even further by the primaries on that monitor (again RGB additive). So no matter how big the document colour space or what methos is used to represent it, when viewed on a monitor, the view is restricted to colour reproducable in the monitor's RGB space.

Dave

[P38942367gj62]

I agree.

Its RGB all the way down.

what I like about Lab is that it is easier to see / understand

how close two "colors" are.

[P38942367gj62]

We know yellow is off the L=50 plane
we know red and  green are on the L=50  plane

I wonder which color is the last one on the plane?

bigger problem is how could you tell?

Yellow is obvious since defined as maximun positive b.

Are there any defined Lab colors between yellow and red?

yellow and green?

[D Fosse]

@P38942367gj62 

Colors aren't exactly L=50 at maximum saturation, except by accident. That's the whole point.

Yellows are brighter - blues and purples are darker. Look at this one for instance:

[P38942367gj62]

Its more of a mess than I thought.

I think I will just give it up here,

save it for another day.

THANK YOU

for your participation : )

[davescm]

Take a look at 3D representations of various colour spaces on Lab axes. It will quickly show you where limitations exist. Argyll CMS has tools to do this (iccgamut, tiffgamut, viewgam) as do various other tools for colour management.

Dave