Why is RGB so important

I am following this thread with interest. Let me first say I work in print (commercial offset and have experience with digital output as well). 

I cannot fathom why RGB values are being asked for as printers (the boxes/machines that do the printing, not the people) do not print in RGB. RGB is additive in that you add Red Green and Blue (typically on a screen of some form) to get white, however printing is subtractive in that we remove the colours (lets use process CMYK) Cyan, Magenta, Yellow and blacK to get white. Same applies with multi colour inkjet.

Secondly if you are able to get the colour defined as a known number from any one of the colour books out there (I use the Pantone system or PMS) then we can extrapolate equivalent RGB breakdowns from these known numbers, as well as web equivalents, etc

Finally the RGB colour gamut is larger than that if most other printing models (one of the most common used is the CMYK system, and yes I am aware or Hexachrome and indeed expanded gamuts of inkjet technologies) so it is possible that an RGB defined colour is not reproducible during conventional printing processes.

So unless I am missing something can some one please tell me why RGB? I haven't touched upon calibration of the devices used to view and reproduce these colours so whilst you can key the appropriate values into any compatible program there is no guarantee that what I see is same as what you will see

Respectfully

Simon

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What's you're saying is that RGB deals with light and CMYK deals with pigments - Old Physics shocker, when it's light, Red and Green makes...Yellow!  When it's pigments, red and green makes...Brown!

With so much being done on a computer nowadays, I can certainly see the benefit of having everything in RGB.  It is extremely easy to convert from RGB to CMYK, versus converting form "Hunter Green" to either one. seeing as how it's software to do the conversion.

RGB is what most basic computer programs think in - which makes sense because the screen is light, not pigment.

It might be really nice if all of our paints had the CMYK/RGB equivalents on the sides.

RGB - the good and the bad

RGB color is being used more because publishing is going digital, and RGB is the color model for SCREEN displays as opposed to CYMK, which is an ink color model for use with paper.

The problem with RGB is screens can have different color settings and various devices can show color differently. Just walk into any video store and look at the picture on the different screens. You will notice different devices render the colors differently.

So having a given set of colors for "official" railroad colors in RGB doesn't help much unless it also includes the monitor profile to match and the monitor used to match the colors has been correctly calibrated. Adobe, for instance, has a set of standard RGB color profiles.

For screen calibration you need a device like this one from Amazon: http://amzn.com/B006TF3746. This is a cheapie calibrator. If you want something like the pros use, there's also this one: http://amzn.com/B007TCISXI. The pro calibrator will enable you to match your inkjet output precisely to your monitor, for instance.

Calibration nightmares

Want to talk about color calibration issues?

I tried an experiment once.  I painted a scrap with some freight car brown (Actually, Krylon primer).  I then scanned that scrap on my flatbed scanner, copied a region of the scanned image, used that to make a larger image, and then printed the result on a photo printer.  The resulting color was not even close!  In order to use the two together, I ended up weathering them both so heavily that the difference was hidden.

It's not just monitors which have calibration issues!

Why RGB

I used RGB values because that is the standard used by both my graphics editing program, and my CAD programs to define a color.  It was also the only values for color I could find as a reference on the internet.  The B&O values I've given, gave good results on printing compared to the color swatches my friend came up with.  These were store paint cards matched to an existing building.  You use what you can find.  Heck, printing the same graphic on different papers (plain, cardstock, photo gloss/matte) gives you different results, in some cases.