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Author   Topic : "Digital pigment mixtures"
Chruser
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PostPosted: Sun Jun 13, 2004 8:50 am     Reply with quote
Well, I've been using various image processing times for quite some time now, although I have not started to paint digitally until very recently. I noticed that Painter mixes colours on a pigment basis by default (yellow+blue=green), although it works nowhere as well as real oils/acrylics/watercolours with the simulated tools I've tried so far. In Photoshop, colours don't mix at all on a pigment basis. Not even CMYK (although this is based on actual pigments while RGB is based on light as far as I know) seems to work for pigment mixtures in PS.

First off, I'm wondering if there are any really good pigment-mixturing programs that allow me to paint in them directly. I may be using Painter improperly, but yellow+blue turns into dark gray, with an almost blacked value, and this is if I have some luck with my mixtures. Sometimes, it doesn't mix at all.

Secondly, is it possible to mix pigments like this in Photoshop?

Oh, and to those of you who idle in the sijuns IRC channel, I love you all. In fact, you're all great people. I thought I'd just say something nice so I'd get more help, but feel free to pretend I didn't confess my sins.
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Impaler
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PostPosted: Sun Jun 13, 2004 10:36 am     Reply with quote
ArtRage is a solid program that has pigment mixture built directly into the painting element.

It still doesn't mix like real-life because it uses an additive model, rather than multiplicative. (I think? I could be wrong about this.) There was a lengthy explanation in a big Painter 8 thread, but I seem to have lost it.

Quote:
Secondly, is it possible to mix pigments like this in Photoshop?


Use Mulitiply as your blending mode (it's easier with layers).
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Chruser
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PostPosted: Sun Jun 13, 2004 10:58 am     Reply with quote
Thanks for your help!

Multiply in PS seems to work great for some colour combinations, but hardly all. Yellow+blue turns into a nice, green colour, but yellow+red becomes the same pure red color as I've selected. It seems to be a dominant colour.

And for artrage, maybe it's just my own inability to choose the right colours, but I find it extremely hard to mix well. To use the yellow+blue example again, you seem to need the exact right tints to even give the mixture a stench of green. I, however, haven't studied colour theory thoroughly, so I may just be missing something.
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Jin
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PostPosted: Sun Jun 13, 2004 11:57 am     Reply with quote
Hi guys,

You won't be mixing pigment at all in Painter since it's RGB, light based color, not pigment or ink based color as used in printing.

To get green with RGB colors, mix cyan and yellow.

Painter 8 Mixer Palette Showing Blue/Yellow Mix and Cyan/Yellow Mix Results:



You'll still get orange by mixing red and yellow.

If you mix colors on the Canvas or on a Layer using brush variants that have blending or smearing characteristics, you'll also pick up existing color on the Canvas or on the Layer (including the Canvas' base color before any other color has been painted over it or the Fill command has been used).

In addition, using brush variants that have blending or smearing characteristics, if you paint over transparent areas of a Layer, your brushstrokes will have white around the edges, or at the beginning of the brushstroke. To avoid that, you can either move the Resaturation slider all the way to the right (either on the Property Bar or in the Brush Creator, Stroke Designer tab's Well section) or check the Pick Up Underlying Colors box at the top of the Layers palette.

If you decide to check the Pick Up Underlying Colors box, be sure to first think whether you'll want to add other colors below that Layer at some time in the future. If you do, the colors picked up from below at this point will probably not look so hot if you add contrasting colors below them later on.



Jinny Brown
Painter Classes at TutorAlley Forums
(new registrations and Painter Classes on hold due to family medical emergency)
Tutorials and Painter Info at PixelAlley
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jfrancis
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PostPosted: Sun Jun 13, 2004 12:05 pm     Reply with quote


** Remember in the example above that 35 * 255 = 35 only when the math is done in zero-to-one space � the number 35 is really 35 out of 255 which is really 0.137, and 255 is really 255 out of 255 which is really 1.0 � so 35 * 255 = 255 only because 0.137 * 1.0 = 0.137 � When Adobe expresses colors in 8-bit 0 to 255 space, they foster a poor understanding of many aspects of image arithmetic.

We can see when we express color mixing in terms of simple image arithmetic that when two pigments are mixed (or when two color filters are sandwiched together) or when two digital colors are multiplied, the resulting color is that color which is present in some measure in both source colors. Pure yellow mixed with pure blue would actually yield black, not green, because pure blue filters only allow pure blue to pass, and pure yellow filters only allow pure yellow light to pass, and so there is no green in the final result because neither filter allows green to pass through.

A greenish blue filter allows some green to pass through. So does a greenish yellow filter. That's why Cerulean blue mixed with Hansa yellow yields a green color.
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Warhead82
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PostPosted: Sun Jun 13, 2004 5:52 pm     Reply with quote
hmm, when i used painter 8, i had no problem, i mixed say blue and red together, and got a purpley type colour, and then i did it with real acrylic paint, and i got close to the same colour. I use it as kind of a guide more, than exact accurate colours. But for me it seemed they were pretty close anyhow.

Try making them equal, dont add more red than blue, or blue than red. ETC
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Jin
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PostPosted: Sun Jun 13, 2004 6:51 pm     Reply with quote
Warhead,

Since my spine tingles and my skin crawls when thinking of figuring out color mathematically, I do it intuitively.. experimenting and finding what I want, or liking what I find.

Most colors don't present the problem that mixing blue and yellow do when you're expecting to get green.

Red and blue do make purple.

Red and yellow do make orange.

Cyan and yellow make green.

It's easy enough, anyway, using Painter's Colors palette with its Hue Ring and Saturation/Value Triangle to pick colors without much effort.



Mixing colors is fun but I don't find it necessary unless I'm blending colors and that pretty much takes care of itself.

Yes, I know it doesn't really take care of itself, but it isn't hard, either. Wink

If you want to mix colors, use ArtRage. Ambient's developers worked with Corel to create the Painter 8 Mixer palette and Mixer brush and the brush technology looks pretty similar in ArtRage, complete with a dirty Oils brush that can be cleaned by dipping it in a glass of water (that would not work with real oils, would it now?... oh well, it's a cute little glass anyway).


Jinny Brown
Painter Classes at TutorAlley Forums
(new registrations and Painter Classes on hold due to family medical emergency)
Tutorials and Painter Info at PixelAlley
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Chruser
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PostPosted: Mon Jun 14, 2004 3:11 am     Reply with quote
Awesome stuff guys, thanks a bunch. The only thing I found somewhat confusing was the "so 35 * 255 = 255 only because 0.137 * 1.0 = 0.137" part. Wouldn't 35*255 equal 35 as previousy stated? *scratches head*

Anyway, I emailed the author of ArtRage with a suggestions about oil paint that can be dried permanently on the click of a button, plus some questions about non-rgb colour mixing.

Matt Fox-Wilson wrote:

Thanks for the mail and suggestions! The drying of paint is something that's been up on our whiteboard for a while, believe it or not. The technology in ArtRage actually supports this, but the product itself does not for a number of complicated reasons best not gone in to here. That said, it is something we are looking at solutions for, and while I don't think the 1.1 version will have drying, we are endeavouring to come up with a way to get it in to further releases in the future.

The colour mixing is done using an RGB model currently, and this is something that also needs attention. We'd like to shift to a more realistic paint model (which is either additive, or subtractive, I don't recall which!) and have been putting a bit of time in to looking at that.

Thanks again for the mail, I can see I am going to have to release info on the update version to the forums (Sijun) as time goes by!


DROOL!
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jfrancis
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PostPosted: Mon Jun 14, 2004 7:34 am     Reply with quote
35*255=35 -- you caught a typo on my part; thanks.

On a new topic:

In the world of light, we often forget there is such a thing as PURE yellow light that cannot be decomposed by a prism into red and green. It's around 470 nanometers.

( http://eosweb.larc.nasa.gov/EDDOCS/Wavelengths_for_Colors.html#yellow )

There is ALSO yellow light that is made up from a combination of red and green. Our brains turn it yellow, and prisms can split it back into red and green. In digital art we live in the RGB world so much where yellow is red + green that we forget that there is such a thing as true yellow light.

In the PIGMENT world it is IMPOSSIBLE to make a pure color. If you COULD make pure colors (one wavelength and one wavelength ONLY, and not combinations of wavelengths) then any two pigments you mixed would make nothing but black. Lucky for us, pigments are combinations of wavelengths. When you mix them, whatever they have in common survives the mix.

Cadmium yellow makes a more neutral green than Hansa yellow does when mixed with Cerulean Blue, because Cadmium yellow brings less green and more red to the table.

Cadmium Yellow and Ultramarine Blue would make an even more neutral green because neither has much green in it to begin with.

---

The way theses programs work is they have to establish a mapping between RGB and wavelength. If you type "RGB to Wavelength" into Google you'll see that while it can be done, there is NO objective external formula for the conversion. Color perception occurs in the brain.
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jfrancis
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PostPosted: Wed Jun 23, 2004 6:38 am     Reply with quote
Jin wrote:

Red and blue do make purple.

Red and yellow do make orange.


* A purplish red and a purplish blue make a vibrant purple because they have so much purple in common.

* An orangey red and a greenish blue make a more neutralized purple, because each brings so little purple to the table to begin with.

* A pure red and a pure blue (if possible to achieve in real world pigments) would make not purple at all, but black, since neither pure red nor pure blue contains any (~400-440 nanometer) pure purple. Purple would not be manufactured in the pure red / pure blue mixing process. It would have to be present to begin with -- as it is in real world red and blue pigments.

* An orangey red and an orangey yellow make a vibrant orange, because they both have so much orange in common to survive the mix.

* A purplish red and a greenish yellow make a more neutralized orange, because each carries so little orange to begin with.

* A pure red and a pure yellow (if they existed in pigment form) would make not orange at all, but black.

Programs like artrage and painter simulate "impure" pigments that reflect colors containing multiple wavelengths.

SONY has invented a new movie screen that only reflects the tight bands of red, green, and blue that its projector emits. Other wavelengths of r, g and b (and hence other ambient colors) are reflected poorly, so the screen looks black to all other light, but reflects a bright tv or movie image -- even in a bright room.

article out about it just today (which is why I bring this up again-- it's fresh in my mind) --

http://slashdot.org/articles/04/06/23/1236235.shtml?tid=137&tid=196
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jfrancis
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PostPosted: Mon Aug 16, 2004 9:37 am     Reply with quote
http://slashdot.org/articles/04/08/16/1418207.shtml?tid=196&tid=1&tid=218

RGB to become RGBCMY

"The basic color elements of television have not changed much since 1954; a half-century after RCA introduced the first color set, the RGB (red, green and blue) system used then still prevails. But Israeli company Genoa Color Technologies has broken the RGB barrier by adding one to three primary colors such as yellow, cyan and magenta, thus expanding - from 55 to 95 percent - the coverage of the visible color gamut. The promised result of this multi-primary color (MPC) technology is a television picture that, with its truer, more vibrant color and brighter image, looks more like cinema than video. Also covered in IEEE Spectrum."

--kind of intersting post today on Slashdot.org
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