Multiply Blending Option is applied to all of these objects. in Fig.A each object has different colors. And in Fig. B, those are all the same color. You can see that in Fig. B the multiply option doesn't take any effects.
My question, is this a normal thing Indesign does? Or is this some kind of a bug? Thanks beforehand.
This is the expected behaviour for 'Multiply' in CMYK modus.
You might be expecting a darker cyan, but that's because you are probably used to the Multiply functionality in RGB mode: the more colour you add, the closer you approach black.
In CMYK that is not the case. What CMYK Multiply does, is add more of each ink used until those are at 100%. It will never, though, add any ink not present.
So 100% cyan and 0% of any other ink will never get any darker than 100% cyan. If you'd add 5% magenta, you'd have to Multiply a lot of objects to reach it, but you'd eventually end up with C100 M100 Y0 K0.
Don't forget that 'Multiply', as any blending mode, functions by manipulating the 'numbers' of your colours. Colours, their numbers, and how they work are fundamentally different in each colour mode.
Indesign has a different behavior with the Multiply mode over spot colors or pure inks. The solution is changing the CMYK values as shown on the squares at the right:
InDesign Secrets has an explanation and solution about it:
When you take two process colors (such as magenta or cyan) and overlap them—multiply them, overprint them, whatever you want to call it—the area of overlap gets darker than either of the individual inks. This happens both onscreen and in the printed output.
If you overlap spot colors, some areas get darker and bolder onscreen. But the printed output may be a different situation. Spot colors are more opaque than process colors, and in the case of this particular job, the designer actually overlapped a single spot ink color on itself. The onscreen result was a lovely interaction among the objects. But in the real world, an orange ink overprinting on top of the same orange ink simply cannot result in a darker orange ink
Adobe is quiet about the actual formulas of their blending modes. Multiply in CMYK mode fortunately isn't especially complex. It's calculated per channel, for ex. cyan numbers do not affect the result in magenta channel.
If we have multiple layers and the top layer has blending mode multiply, the resulted image below the top layer is calculated at first. Then the top layer is taken along with th the following formula:
the resulted CMYK value of all layers = (1-X)*M + X ,where
X = the bigger one of the CMYK values when the top layer value and the calculated value from the rest of the layers are compared
M = the smaller one of the CMYK values when the top layer value and the calculated value from the rest of the layers are compared
All CMYK values are presented in scale 0...1, where 1 means 100%
For example, if the top layer has cyan=50% and the rest of the image has cyan value=30%, the resulted cyan = (1-0,5)*0,3 + 0,5 = 0,65
that formula cannot give bigger cmyk values than 1 (=100%) which is already presented without math by others. Your 100% cyan and another 100% cyan gives cyan = (1-1)*1+1 = 1
Unfortunately I cannot give any established source for this formula, it's calculated from few samples by assuming it has nothing else than a sum and product weighted.
