How does Adobe figure out the multiply value?

[tbowat]

Lets say; I have a object that is colored 40% of pantone 289 and it has a multiply effect applied in Illustrator, then it is placed in InDesign over an object that is colored 87% of pantone 289. Where those %'s overlap the value is 92%. How does Adobe come up with this number?

Thanks

 

[Stephen Marsh]

Adobe, generally state that this is a trade secret and they don't go into the math in depth.

Adobe Help for Multiply blend mode: "Multiply Looks at the color information in each channel and multiplies the base color by the blend color. The result color is always a darker color. Multiplying any color with black produces black. Multiplying any color with white leaves the color unchanged. When you’re painting with a color other than black or white, successive strokes with a painting tool produce progressively darker colors. The effect is similar to drawing on the image with multiple marking pens."

Here are some links that go into blending modes in more depth. Most of the math is based around RGB, so when it comes to CMYK or spot colours things may behave a little different for some modes.

http://dunnbypaul.net/blends/
Blending Modes: The Real Deal | Selections: The Key to Compositing | Peachpit
Layer Blend Modes Explained!
Blend Mode Math, CHOPs etc. - RetouchPRO
DIY Academy: Photoshop: Blending modes - Digital Grin Photography Forum
Adobe Design Center - CS3 Adobe Video Workshop


Stephen Marsh

 

[leonardr]

Lets say; I have a object that is colored 40% of pantone 289 and it has a multiply effect applied in Illustrator, then it is placed in InDesign over an object that is colored 87% of pantone 289. Where those %'s overlap the value is 92%. How does Adobe come up with this number?

All of the math for the various blend modes are specified in the PDF standard (ISO 32000-1:2008).

Also remember that in the case of rendering spot colors on screen (where no actual inks exist), the alternate colorspace (either CMYK or Lab) has to be used. That includes simple rendering as well as blending - so in this case, you are actually seeing the CMYK or Lab values blended together. Only on a real press would you see ink blending.

 

[Glenn McDowall]

(100-87)*((100-40)/100)=(100-92.2) rounded to 92