Inspiring

Question

Multiply blending mode

Forum|Forum|8 years ago
April 25, 2018
4 replies
16586 views

Hello,

I thought I understood how this worked but apparently I don't.

Illustrator's user guide states: How to edit artwork using transparency and blending modes in Illustrator

Multiply

Multiplies the base color by the blend color. The resulting color is always a darker color. Multiplying any color with black produces black. Multiplying any color with white leaves the color unchanged. The effect is similar to drawing on the page with multiple magic markers.

In CMYK space, if I have an object filled with 30 0 0 0 set to multiply on top of another object filled with 30 0 0 30, I get for the overlap 51 0 0 30 !! I am no longer sure what I was expecting but it would have probably been 30 0 0 30. My question is:

1- how does "Multiplies the base color by the blend color" actually operate on the numbers to get to 51 0 0 30?

I had to check this in Photoshop to get the resulting value. So my second question is:

2- how can I check the resulting colour value directly in Illustrator?

This is for CS4.

Thanks.

This topic has been closed for replies.

angie_taylor

Legend

Also, I seem to remember that with Multiply mode the top layer’s numbers are inverted before being multiplied with the bottom number?

c.pfaffenbichler

Community Expert

Both numbers are translated to a value between 0 and 1 with 0 being »dark« and 1 being »light«.

So for 30% on 30% that would be (1 - 0,7 x 0,7) x 100.

Ton Frederiks

Community Expert

Let's put Pantone aside for a minute. I created a custom swatch in Illustrator with CMYK values and set it to spot, rather than process colour. I then created an object filled with the spot colour (let's call it S) and another object filled with same the CMYK values as the spot colour, but as regular process colours (let's call it P). I then create a third object filled with some process colour that serves as my base object (let's call it B). To my surprise, I can get a different result when I set S and P to mutiply on B. Likewise, I can also get different results when I set S and P to overprint on B. I was expecting the result for S and P to be exactly the same when comparing multiply and multiply together, and then when comparing overprint and overprint together (because S and P have the "same" CMYK values). Please explain what I am missing. Note that I am not comparing multiply with overprint here.

For example, try:

S (spot colour): 30 30 0 0;

P (process colour): 30 30 0 0;

B (process colour): 20 90 10 0.

With Overprint Preview Off, the preview is what is send to a color printer.

With Overprint Preview On, I cannot explain the difference between Spot and Process Multiply.

With Overprint Preview On, Spot Multiply and Overprint is as expected, it is treated as a separate ink, that does not share inks with the background color.

With Overprint Preview On, Overprint Process is correct too. Because the Overprint Process color shares Cyan and Magento with the background color, these inks will not overprint. But the Yellow is not shared and will show, 10% gets added to the C30 and M30.

c.pfaffenbichler

Community Expert

In CMYK space, if I have an object filled with 30 0 0 0 set to multiply on top of another object filled with 30 0 0 30, I get for the overlap 51 0 0 30 !! I am no longer sure what I was expecting but it would have probably been 30 0 0 30.

You might be confusing the setting »Overprint« and the Blend Mode »Multiply«.

This is not the actual math but it might help illustrate nonetheless:

The base Layer’s 30% are the base, you multiplying 30% onto it means that

• 30% of 70% (the difference between the base’s 30% and 100%) get added to the 30%.

(0,3 x 70) + 30 = 51

Ton Frederiks

Community Expert

If you are interested in how Blend modes work, see the PDF Blend Modes Addendum

Blend modes addendum

It is not simple (at least for me) and it seems to convert the colors (RGB or CMYK) to some intermediate HSL representation.

Doug A Roberts

Community Expert

I think that just applies to the Hue, Saturation, Colour, luminosity modes Ton. the other blend modes contain the usual formulas I've seen before.

the key bit here is this:

"The above formulas apply to RGB spaces. Blending in CMYK spaces (including

both DeviceCMYK and ICCBased calibrated CMYK spaces) is handled in the following

way:

• The C, M, and Y components are converted to their complementary R, G, and B

components in the usual way. The formulas above are applied to the RGB color

values. The results are converted back to C, M, and Y.

• For the K component, the result is the K component of Cb for the Hue, Saturation,

and Color blend modes; it is the K component of Cs for the Luminosity

blend mode."

So it does do an RGB conversion.

Doug A Roberts

Community Expert

i can tell you how it works in RGB.

each blending mode is an equation with the colour value of each channel converted to a figure between zero and 1 (zero is 0, 1 is 255)

so a yellow value of 100 is input as 0.39...

multiply, for example, is (background colour x foreground colour).

because both values will be less than 1, you end up with a lower number than you started with. thus, the colour value will be darker (closer to zero).

this doesn't work with the CMYK values, because they're percentages with the darkest value at 100%. I'm not sure, but i suspect the blend mode is actually doing the maths on an RGB conversion of the CMYK colour.

Doug A Roberts

Community Expert

either that, or there's some internal formula for the value of overprinting inks (which is the real-world analogue of Multiply in CMYK).

c.pfaffenbichler

Community Expert

either that, or there's some internal formula for the value of overprinting inks (which is the real-world analogue of Multiply in CMYK).

Equating »Multiple« with »Overprint« would be a mistake; in »Overprint« any Channel of the overprinting object that contains non-0 values takes precedence, those that contain 0 are ignored.

An object of the CMYK color 1/1/1/1 set to overprint on any other CMYK background (like 0/100/100/0) would result in 1/1/1/1.

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