Transparent vector colours?

[photoken]

PL seems to give an unexpected result when a vector layer is made transparent.

For example, given this as a starting point:

colours 100.png

The blue circle and yellow rectangle are on separate layers. If I reduce the transparency of the yellow rectangle layer to 50%, I get this:

colours 50.png

I expected the area of overlap to be a green, as shown in this vector drawing done in CorelDraw:

cdr.png

[Hoogo]

The maths for the colors are correct.
128/128/255 is light blue
255/255/0 is yellow,
192/192/128 is the color in-between, that's surely a faded yellow.

The light blue of the version of CDraw is a bit different, it's 102/153/255, that's more green and less red.

[photoken]

The maths for the colors are correct.

Hmmm...I suppose.... It just seems weird -- I'd expect that at some point the blue showing through a transparent yellow would look distinctly green.

[Hoogo]

Maybe you too have learned in school with watercolors that you can mix yellow and blue to get green? At least for me, that's somehow "in the flesh", though I know that they were wrong.

Its cyan instead of blue, CMY. Blue and Yellow are complementary colors, mixing them as pure colors will result in grey.

[bkh]

The maths for the colors are correct.

Hmmm...I suppose.... It just seems weird -- I'd expect that at some point the blue showing through a transparent yellow would look distinctly green.

The blue in the Corel example is quite different from the PL example (the Corel blue is closer to cyan, the PL blue has a tendency towards purple). If I use the same blue as in the Corel example, then the mixed colour in PL is the same as in the Corel example.

Cheers

Burkhard.

[photoken]

Yep. When I tested using the same shade of blue in CDR and PL, the results are the same. Too bad I never could remember the differences between additive and subtractive colours....

But that leads to an interesting question: What would be the best way have my example look as if it were a yellow square painted on top of a blue painted square, allowing the colours to "mix"? Still staying with vectors, and (hopefully) allowing me to easily vary the intensity of the colours to achieve different "greens" where the two colours overlap.

[bkh]

But that leads to an interesting question: What would be the best way have my example look as if it were a yellow square painted on top of a blue painted square, allowing the colours to "mix"? Still staying with vectors, and (hopefully) allowing me to easily vary the intensity of the colours to achieve different "greens" where the two colours overlap.

I'd use "multiply" layer mode and make sure the mixed colours are not too "pure" (make sure the blue contains enough green). "Multiply" will also interact with the background, so you may have to put the vector layer into an isolated group (see the sample file).

mixing colours.png

Cheers

Burkhard.

[photoken]

so you may have to put the vector layer into an isolated group.

Thanks for the tip about creating an isolated group -- works well. I found that changing the blending mode (of the yellow rectangle) to "Color" works a little better: its transparency can get a little below 60% before the overlap becomes mostly gray, while "Multiply" poops out around 70%.

overlap.png