Problem with CMYK settings

Scratchpole's picture

Just making an ident for a performance and trying to follow a graphic designers instructions: I set some cmyk values numerically, change values on another colour and when I go back to the first it has changed. Any idea why? I guess it's an RGB/cmyk conversion thing but it's buggin me.

Also what can I do to avoid the outline around my text? Cheers in advance.

Picture 10.png
Picture 10.png279.82 KB
TakeoverlogoFlat.qtz10.92 KB

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mattgolsen's picture
Can you give a little more

Can you give a little more explanation in what you're doing? CMYK should only be used for print AFAIK, so I'm unsure of why you're converting from RGB...

Scratchpole's picture
I am following a print

I am following a print designers colour palette. Using the cmyk sliders for a billboard.I set the numbers to her instructions but when I return to the settings they have changed. Here is the draft qtz for you to take a look at anyway: I'm planning on making the particles subtly sound reactive.

TakeoverlogoFlat.qtz10.92 KB

cwright's picture

This happens because, deep down inside, colors really want to be RGB, and QC stores them as such. When you input them as CMYK, it converts them to RGB internally. When you call up the CMYK editor again, it doesn't have CMYK values anymore, just RGB. so it converts the RGB value to CMYK, and provides those values in the editor (which are different)

It's impossible for RGB's 3 dimensions to map exactly to CMYK's 4, so some rounding/massaging takes place to make it all happy.

If you really need accurate CMYK values, stop what you're doing and get some adobe software -- anything touching the GPU will switch to RGB/YUV behind your back, and you'll lose some data. (I'm not a print nerd, so I don't know how significant that is -- to me, 3 color dimensions seems like enough [or technically, 1 luma dimension and 2 chroma dimensions, as found in yuv]) Remember that QC is aimed at efficiency over accuracy. (adobe's gpu-acceleration no doubt takes cmyk color space into consideration -- qc does not)

gtoledo3's picture

The reason why it's so important is because most machines feature actual cyan, magenta, yellow and black (k). When you see stuff come to print that doesn't have the proper color profile conversions coming across, you can wind up with a confused machine that prints all colors to create black... which typically looks really ugly, and betrays the jitter or lack of alignment of the machine.

IMO, what SHOULD happen is that everything should work in RGB every step of the way, and have a decent r.i.p/color profile setup for the particular print job. It can be cool to do everything in cmyk, but... the cmyk doesn't usually come to print looking right without color profiling anyway, so WHAT is really the point of color switching back and forth a million and one times during the process... Many setups have all kinds of "spot color" options that people never touch, and are a good way of ensuring you get what you want.

I basically see next to no point in "creating" using cmyk in REALITY, but the industry is king of stacked against me on that one. There obviously IS a point if you are trying to sell someone something based in that theory of process...

There is a bit of "rant" in this, and sorry if none of the comments are constructive!

cwright's picture

The "lots of colors = black" hack is actually called "composite black", and isn't related to colorspace conversion. You can do sloppy conversions to produce that (i.e. converting RGB to CMY, leaving K at 0), but that's still a software issue.

I completely agree on when colorspace conversion stuff should happen (exactly twice: once at input, once at output.), but that's a rant for another day.

Either way: doing cmyk in qc is like trying to do raytracing in opengl -- you could make it work with a lot of work, but why would you want to?

gtoledo3's picture
To clarify, I guess what I

To clarify, I guess what I mean is that I've seen certain setups where type "should be" black(k), but it pulls from the other colors (agreed, definitely caused by software being setup/used incorrectly).

To finish my rant, I also take great exception to the thought (that many have) that anything that you see on a computer screen could ever truly reflect real "printed" cmyk values, simply because of the fact that "white" is only a byproduct of the paper used, whereas it is typically "different" on the screen. To get real color reproduction, you typically have to use way more colors, including some that mix "white" into the actual ink or toner.

None of this is helpin' our boy out much though! All I can say, is that if I was working on something that had to get cmyk correct on the screen, and someone anal was going to be comparing it against print output... I would be friggin' crying about now. Actually, I would never agree to it!

Scratchpole's picture
Yes well that cleared it all

Yes well that cleared it all up nicely!?! Anyhow once it hits a 20' screen via stage lighting it'll all be about 20% different and i'll probably use some B/C/S to make it look half decent.

The other question about the outline seemed to get lost though and the only workaround for that i have found is the glowing apple/blur rather than bloom. Thanks for the replies so far.

gtoledo3's picture
I think that outline is

I think that outline is inherent to the bloom filter... hmmm. Doesn't seem like I get it when I take it out of the equation.... you are prob right about using the blur instead, if it doesn't matter too much.

I actually use the bloom and gloom BECAUSE of the outline all the time!