6 Replies Latest reply on Aug 19, 2014 3:34 PM by Alp Er Tunga

# How to calculate blend modes in Lab

When calculating blend modes in Lab mode, to which range I should convert the values of the a and b channels?

• ###### 1. Re: How to calculate blend modes in Lab

That question does not make sense.

• ###### 2. Re: How to calculate blend modes in Lab

Can you explain briefly?

• ###### 3. Re: How to calculate blend modes in Lab

No, because the question you asked makes no sense.

Try giving us more information about what you are trying to do.

• ###### 4. Re: How to calculate blend modes in Lab

When calculating the results of the blend modes in RGB, I convert the R, G and B values to 0 - 1 range, then find the result of the blending.

In Lab, I tried to convert the values of the a and b channels to the -1 to 1 range, but I could not success.

For example, let's say I want to find the result of multiplying a layer with itself in Lab ... and the color of layer is L: 53, a: -54, b: 23.

Ps gives the result as L: 28, a: -85, b: 42.

How can we find the same result?

• ###### 5. Re: How to calculate blend modes in Lab

You shouldn't even have to convert RGB values to 0..1 range to calculate the blend modes, assuming you have some basic math knowledge to normalize the result.

LAB is represented with L ranging 0 to 255, and the a* b* channels ranged -128 to 127 (stored with an offset of 128).

For normal mode blending, the range representation doesn't matter.

For Multiply, the offset nature does matter for the a* and b* channels.

• ###### 6. Re: How to calculate blend modes in Lab

Normalizing at the end is ok for RGB ...

But, in Lab, I'm afraid that I can not understand without a real example.

If you have time, can you write the math for my example for a single channel?

a: -54

Multiplied by itself, then it becomes a: -85.

How can we get this result for a?