Author Topic: Two questions about colours  (Read 1847 times)

JohnB47

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Two questions about colours
« on: June 18, 2016, 01:42:51 pm »
OK, first question. I'm using Scribus version 1.4.6

With a document open, I choose Edit/Colours, then New. I select whole numbers for the CMYK values, say 50, 40, 30, 20 and give the colour a name, then click OK. Then I immediately go into Edit and find that the colours have changed to 49.80, 39.20, 20.0 and 10.2 If I then reset them to the whole numbers again, some of them stay at the whole number, others revert to an 'almost' value.

Surely this isn't right?

Secondly, a question about the colour wheel. I can see how you drag the little dot around to select a colour but how do you select the colour depth or lightness/darkness? Say I select a certain blue, how do I select a darker or lighter version of that blue?

Thanks for any help.

Nermander

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Re: Two questions about colours
« Reply #1 on: June 18, 2016, 09:58:53 pm »
I am not 100% sure, but I think the numbers issue is because the numbers are percentage (0-100) but are stored as a byte value (0-255).

50% of 255 is 127,5, it will be stored as 127.

But 127 of 255 is 49,80 %.

JohnB47

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Re: Two questions about colours
« Reply #2 on: June 18, 2016, 10:24:13 pm »
Hmmm. OK, maybe so. Seems a bit odd though but not a big deal. I just wondered.

Any idea about my second question - how to select not just colours but lighter and darker versions of those colours? I'm sure its a  really easy answer but I can't work it out. I've read the Wiki on this but can't see it mentioned.

Thanks for the reply.

GarryP

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Re: Two questions about colours
« Reply #3 on: June 19, 2016, 03:18:30 pm »
To add to what's already been said on your first question: The question really is, are you using properly configured colour management?

If you're not then don't worry about it. The difference between, for instance, 50% and 49% yellow will be so small that no-one will notice.

On the other hand, if you are using properly configured colour management then that's another issue which brings up the idea that Scribus can't properly handle colours. For example, if you set a colour to be 50% and Scribus changes it to 49% then I'd say that that was wrong. If an official colour has specific values then Scribus should be able to let you use those specific values. If it doesn't then - to me at least - it's not doing things right. That's just my opinion.

I think the short answer to your second question is that there isn't a way to select lighter/darker colours (it's a fairly limited tool at the moment). (See this wiki page for more information: https://wiki.scribus.net/canvas/Discussion:_Improvements_to_the_Colour_Wheel_and_Solid_Colours although it was created in 2010.)

You might like to try this online tool instead: https://color.adobe.com/create/color-wheel/

You have to copy/paste the numbers into Scribus but you get much more control over what you can do and you can create a palette from an image.

P.S. I created a feature request - https://bugs.scribus.net/view.php?id=12942 - a while ago about letting users copy/paste hex values for colours but I've no idea if that will ever be implemented since it's not been modified since I created it.

JohnB47

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Re: Two questions about colours
« Reply #4 on: June 19, 2016, 07:56:26 pm »
Thanks Garry. That clears things up nicely.

Re first question: No I'm not using properly configured colour management - I wouldn't know how to. It's no big deal but I agree - if a user is offered the opportunity to put in % values, they should stick. Although I take the point made by Nermander.

Thanks for the colour wheel - looks complicated but I've got it working fairly well after a short while.

Just to finish off, I can't see hex values mentioned in Scribus anywhere. If I wanted a value for a particular colour, where would I find it?

Thanks again.

GarryP

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Re: Two questions about colours
« Reply #5 on: June 20, 2016, 02:46:23 pm »
You're welcome.

I don't think anyone could come up with a good reason - that wasn't on a purely coding-side of things - that could justify Scribus changing input values by itself.

Maybe if the values taken together were out of gamut then a warning could be issued but the software shouldn't make changes just because of the way it's been coded. (It makes me wonder how accurate the palettes supplied with Scribus are if percentages get "converted" to byte values in the range 0-255 as mentioned by Nermander.)

That colour wheel is quite complicated and probably has way more functionality than most people need but it's worth using until Adobe start charging for it! (That's just a joke, I hope.)

Currently Scribus doesn't allow hex values for colours, which is a shame. My request was to add functionality to be able to do so. This would allow us to easily copy colours from/to Scribus, GIMP, CSS, etc. (Obviously this would be for RGB colours only but it would still be useful to a lot of people.)

a.l.e

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Re: Two questions about colours
« Reply #6 on: June 20, 2016, 04:05:05 pm »
this is a general problem with scribus: imo, each time a value is converted, scribus should also store the original value (with its unit) so that that value can be used in the context where it's further converted or converted back to it's original value.

not trivial to implement, but there are several places in the code where similar problems arise.

GarryP

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Re: Two questions about colours
« Reply #7 on: June 20, 2016, 04:45:20 pm »
A very quick rummage through the code shows that Scribus seems to use a mix of ints and uchars (and even doubles sometimes) when it deals internally with colours. Probably just how it has evolved over the years with it being easier to code one way than another for particular functions.

I guess it would be a nightmare to unravel it all to make it use floats (to cope with, for example, 45.5% yellow) everywhere but doing so could mean that the original values could be kept "nice and fresh" while quick method calls could be used to convert them wherever needed.

That's probably a massive over-simplification on my part though and it's probably way more complicated than it looks at first what with having to cope with RGB/CMYK/HSV/etc.

Maybe a device-independent colour model - such as L*a*b* - could be used internally? And maybe I'm talking rubbish as I'm out of my knowledge zone now!

All-in-all, this is interesting but very complicated stuff.

JohnB47

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Re: Two questions about colours
« Reply #8 on: June 20, 2016, 07:04:26 pm »
Thanks for that further reply Garry and thanks to a.l.e also. This conversation is way out of my league now, so I'll leave it there.

Cheers.