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Question

Multiply blending mode

Forum|Forum|7 years ago
April 25, 2018
4 replies
16467 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.

ceyhun_akgun

Legend

Thank you very much c.pfaffenbichler and theangietaylor (the angie! for a reason) for your input. This really turned my (mis)understanding of multiply and overprint upside-down.

Let me summarise what I gathered from what you said. Please correct anywhere that I may be wrong.

MULTIPLY

-First of all, multiply applies channel to channel (each channel is independent). This is in line with the Adobe document referenced earlier by Ton (Blend Modes Addendum) which refers to multiply as a "separable" blend mode.

-To determine the result of multiply, there is no conversion to any other space. This too is in line with how I read the Adobe document.

-In CMYK, say the the Base object B has values Bc Bm By Bk, and the Top object T has values Tc Tm Ty Tk. T is set to multiply.

For the C channel (Cyan), the operation is:

To simplify, all values are first divided by 100 to get a C value between 0-1. The final result Rc is then muliplied by 100 to get a C value between 0-100.

Rc = Tc*(1-Bc) + Bc

The same operation applies to the M, Y, and K channels.

The Adobe User Guide states for multiply:

"The resulting color is always a darker color". Let's check. Rc = something positive + Bc >= Bc. True.

"Multiplying any color with black produces black". For black, Tk=1. Rc=Tc*(1-Bc) + Bc = some value. Likewise for the M and Y channels. For the K channel, Rk=Tk*(1-Bk)+Bk = 1*(1-Bk)+Bk= 1. So the result is Rc Rm Ry 100. True.

"The effect is similar to drawing on the page with multiple magic markers". That, I can't say!

OVERPRINT

-Overprint applies channel to channel (each channel is independent).

-To determine the result of overprint, there is no conversion to any other space.

-In CMYK, say the the Base object B has values Bc Bm By Bk, and the Top object T has values Tc Tm Ty Tk. T is set to overprint.

No need to alter values (divide by 100) here.

If Tc > Bc, Rc = Tc, else Rc = Bc

The result R would then be composed of values from both B and T, depending on how they compare for each channel.

Another notable aspect is that both effects are profile/colour space -independent. This brings me to cyhun-akgun's statement "When you multiply, the color values in the blend vary. So, the upper color and the lower color do not mix at 100%".

Is what ceyhun is observing a result of printer intervention (RIP), for example, to limit the amount of ink used? That would then not be related to multiply as such but to the printer. ceyhun, do you observe that in Illustrator too or simply in print?

Is there a document you (c.pfaffenbichler or angie) can point me to that fully describes these two operations?

In blending modes, MULTIPLY is the clearest what will be the result.

Multiply and Overprint use are mixed. They are not the same, they do not give the same result.

Apart from digital and offset printing, the small values in the color values for flexo and gravure printing are very important. Points that are never seen due to dot gain values can print out.

Photoshop does not display pixels below 1 in the info panel. But at 0.5% color value, 30% point gain is a very different color value. This is caused by the operations in the CURVE curve in RIP.

For all these reasons, I prefer to print out the blend modes flattened. All color values must be in my control.

Graphic Designer Educator / PrePress Consultant

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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