Beyond RGB Color Matching

[cedarwoodron]

I have successfully used straight-forward RGB color matching on a number of occasions when trying to get a particular paint color for a given prototype; however, recently, I have been trying to match what would appear to be a red oxide primer paint color (RGB= 140-42-29) for purposes of printing decals on white decal paper (which I then apply to the painted surface and blend the inevitable white edges of with a brush tipped in the same color).

I used the Trainz list of RGB colors (Sample Railroad Colors)- which I downloaded and printed out- to develop a subset of "reds" based on their visual affinity to a painted (red oxide primer) styrene sample strip, but when I printed that subset sheet out, using bright white paper, it seems as if all of those samples I chose vary only slightly from each other- and are not really close to the sample color strip. I tried scanning the painted chip and adding it to the subset sheet, but again, a similarity to the other chosen colors was the only result. I know that there is also another adjustment to a given RGB color for hue, saturation and lightness (HSL), but I have no clue as to how to go about that (toning down or up the given color?).

Does anyone here on the forum use this HSL adjustment in modeling?

[BroadwayLion]

You are mixing Apples with Space Junk. RGB colors are monitor colors, that is subtractive (light passing) colors (Primary colors = Red, Blue, Green). The accuracy of these colors depends on the accuracy of your monitor. A professional print shop would use monitors costing thousands of dollars and can be precisely adjusted. But then they would not be using the RGB schema, instead they would be the CYMK additive (opaque) colors (Primary colors are Yellow, Red and Blue) for which your printer has precise formulas for mixing the ink for his press. Indeed, the .pdf files that you pass to your printer (when using the x2 settings on your .pdf application) will have the exact CYMK codes embedded in the .pdf so that he will not have to guess at what color you actually specified.

Ok on the monitor they will look, but they translate best to the press. When you, lowly primate that you are, try to print them on your printer, you are at the mercy of the quality of your printer. One with six ink tanks is better than one with three ink tanks. And look at your ink tanks They are labled C Y M and Black or K.

The bottom line is "You cannot get there from here!"

The bottom of the botom line : LION says perfect color matching is STOOPIT, as soon as the train leves the paint shop it begins to fade and collect dirt, so that it will not match any other car on the consist anyway. And as for printing decals, nobody even thinks that the model was made with the degree of accuracy that you need to match a swatch from your printer. Far better is to make a frame around your decal, perhaps a black or white border, so that the rivet counters will not notice the subtle shades of dirrerence. The briliance of your white paper will also affect the quality of your finished product.

ROAR

[dstarr]

I take it that your real problem is color from your printer doesn't match a paint chip?  Your objective is to create white lettering decals by using a white decal paper and having the printer fill in the background around the white lettering with a boxcar red that matches the paint on the car? 

   RGB and HSL are different "color spaces"  .  RGB is encoded as three strengths (values) per pixel, one for red, one for green and one for blue.  HSL, Hue, Strength, Lightness, encodes each pixel as a value for hue (angle on the color wheel)  a measure of how much white is added to move the color from white, thru a hint of color, to a really saturated color, and lightness, (brightness).  You can get the same colors in any color space.  HSL is a nice for adjusting colors,  you can alter the Hue variable to change the color without altering the Saturation of the color, or you can alter the Saturation to fade the color out, or in, without changing the color.   Your computer can convert from one color space to another, given the right software.   Was I trying to match a color by trial and error and by eye, I'd prefer to do it in HSL colorspace.(Also known as HSI, HLS, and HSV colorspace).  I don't have this kind of software mayself, but I assume that you can find image manipulation software that can convert from one color space to another.  At a guess, GIMP can do it, GIMP can do anything,  if you can figure out how GIMP works, given the miserable documentation.  

You should not expect the color on your monitor to match exactly the colors from your printer.  They will be close, but not so close as to give a flawless color match.  Color of paper is important in printers.  Does the color look the same printed on white paper as opposed to the white decal paper?  I'd bet it doesn't.  

   All I can recommend, is to make a LOT of test color patches by fiddling with the colors and printing them out until you get a good match.  Fiddling in the HSL color space will be a little easier than fiddling in the RBG color space, but you can get the job done in either. 

[cedarwoodron]

So perhaps tweaking the hue may give me some greater matching flexibility (given full saturation)?

Looks like a second set of hue variations of those samples closest to the plastic swatch chip might move me closer to a desired match.

Cedarwoodron

[RDG Casey]

Be aware too that there are colors out of the CMYK spectrum in printing. The more vibrant colors are made with PMS colors that use a base of transparent white. Since a normal inkjet printer does not print white it is impossible to reproduce some colors. I would guess opaque paints would have some white in them as well making the same scenario.