Inspiring

Question

BUG: overprint preview on working for white colors

Forum|Forum|2 years ago
September 12, 2023
2 replies
1048 views

Create a blue rectange, put white spot-color text onto it.
Change text to overprint.

-> in overprint-preview, text should now be some light blue, but it is invisible instead.
solution: spotcolors of p% opacity should change color to (1-p)*below_color + p*spot_color

Bug

This topic has been closed for replies.

Lukas Engqvist

Community Expert

How is your white spot colour defined. You can define a spot colour to have any appearance. (I normally will make it Pink or some bright green depending on colours that do not appear in design).
If you are using a blue rectangle use a colour that will show on blue.
White will show as darker since it is overprinting.

Spot colours may be defined any colour model, but must be displayed as "Overprint" so that you can judge trapping etc. Spot colours that overprint can not display as knocking out what is under.

LordrhavinAuthor

Inspiring

My white is defined as a spotcolor with a CMYK-representation of 0/0/0/0. I know how I can circumvent the bug (give it some other representation), but a bug is still a bug and should be fixed. The internal color model is probably CMYKA (a=alpha), because you cant do tranparancy otherwise, so this is just a mathematical issue. I've doing colormath in multiple additive and subtractive colorspaces for a long time. I know what is going wrong here. You dont even need a fifth color, CMYKW can be translated to CMYK' by allowing K' to be -100 to +100 internally as they basically neutralize each other to K'=0 what then would be K=50 in a pure CMYK colorspace.

E

Eugene Tyson

Community Expert

If you can tell us what you're trying to achieve we can help you out and get it setup right.

E

Eugene Tyson

Community Expert

White is C0 M0 Y0 K0

Set to knockout you see below the blue rectangle - as it 'knocks out the background'

Set to overprint and you see nothing 0% ink.

If you want White - it's best to use an Off White to represent the White

Make it C20 M20 Y20 K20 - as a Spot colour

Then white ink can be applied at the printing stage

You only really need this if printing on transparent stock - like acetate or labels.

If you want to see the paper stock underneath - if it's white - then use Paper

If you use Paper on a transparent stock (like acetate or a label etc) you will see right through the label to your hand.

For this reason - on transparent stocks of substrate - it's best to use a Faux White colour to represent your white text or backgrounds that should be printed with white ink.

LordrhavinAuthor

Inspiring

Its not helpful and wrong. First, white as a spot-color is not CMYK 0/0/0/0, that is just its screen representation in a CMYK-to-RGB setup. Actual white would be C0 M0 Y0 K0 W100 while in case of printing C0 M0 Y0 K0 is just "none".

The thing that is wrong here is the colormodel providing print preview. A Spot-Color is not a CMYK processing color and has to be handled different. As stated the correct way to put a White 80% color in a CMYK-model atop a 50/50/0/0 CMYK-blue would be:

80% * of 0/0/0/0 = 0/0/0/0
+
20% * of 50/50/0/0 = 10/10/0/0

= 10/10/0/0 in CMYK

Lukas Engqvist

Community Expert

I understand what you are saying, and how you would like for spot colours to be dispayed as opaque simulation… Spot colours are used also for metalicts, varnishing and embossing where these are not visible, but still need to be represented on screen, yes it is possible to render a simulation of print, but this is not what overprint preview is.
I would suggest trying a software like Esko Studio. It is pricy but it does the kind of simulation you ask for.

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