Part 1: A Look at Color Proofing
This tutorial gives some background on color proofing and explains what to do when the color you print doesn't match the color you chose on screen. There will be future tutorials that expand on the topics mentioned here.
Step 1: How Color Works
In previous articles we have mentioned that Stratasys J750 users might find that the color they selected on their monitor doesn't match the color on the part they are printing. We explained that this is because computer monitors use the RGB color gamut while printers (both 2D and 3D) print using the CMYK color gamut. Each gamut has its own slightly separate range of colors.
We also explained that printing software (both 2D and 3D), therefore uses a color profile to remap the colors that fall outside the CMYK gamut.
One way to make the colors match is to take the RGB color that you would like to create and, using a software package like Adobe Photoshop®, compare that RGB color to the CMYK color the printer will output instead.
After you see the colors on screen side by side, you can adjust the color that will be printed till it best matches the on screen RGB color. This process is called color proofing.
Color proofing helps avoid surprises and can simulate which colors can be printed with a good match and which will be mapped differently.
This is a good time to note that no printer, whether 2D or 3D, can reproduce the full range of colors that can be represented on a monitor. A monitor is based off a light source and printed objects are not. Certain vivid and fluorescent colors will simply never look as bright without a built-in light illuminating them.
Step 2: Soft Proofing
Soft proofing involves displaying the desired RGB color on screen and matching it against a simulation of its CMYK translation on screen (for example, with Adobe Photoshop®).
A number of adjustment techniques can be applied to achieve the soft proofing process. After adjusting the J750 proofed colour a closer match to the RGB Red can be achived
Remember that the original RGB value selected here only exists on screen. A computer moditor uses a light source to reproduce colour many of these highly saturated colours are impossible to print on any platform 2D or 3D
We will be publishing additional tutorials on how to carry out these adjustments in the future.
In addition to using a powerful software package like Photoshop to view and accurately adjust colors basic soft proofing can be achieved through the use of GrabCAD Print where an indication of the actual color to be printed will be displayed on screen
Step 3: Hard Proofing
Hard proofing involves taking the desired color, usually off screen via a physical color sample or swatch (but we’ll explain what to do if you do not have that in a future tutorial), and printing hard copies of that color via GrabCAD Print until the colors match to your satisfaction. This can also be referred to as color matching.
Step 4: Which One To Use
Should I use soft proofing or hard proofing?
Soft proofing is faster and cheaper, because you can easily simulate the original and desired color on screen in order to compare them.
Hard proofing is more absolute and accurate, because you can hold the two colors in your hand and compare them off the screen.
Typically, both methods will be used for both 2D and 3D printing. Printer operators will first soft proof and then do a test print to see the color in real life before committing to a full-size print.
We do not recommend either of the following compromised methods of color proofing:
1) Taking the hard copy of the desired color and matching it against colors printed on paper in 2D, instead of colors printed on objects in 3D.
2) Matching a physical color chip against a color you display on screen.
Step 5: A Note About Rendering Intent
We also mentioned in our previous piece on color that there are a number of techniques a pre-printing software like GrabCAD Print can use to remap colors from RGB to CMYK; two common methods are through absolute rendering or relative rendering. Adobe Photoshop® can show you the difference between the two rendering intents.
Let’s look at what is going on behind the scenes when these rendering intents are applied. The animation below shows how colors within both the RGB and CMYK color spaces are remapped when these rendering intents are applied
In this example we are simulating what occurs when translating colors using the Absolute and Relative rendering intents. We have some colors that fall within both color spaces and some that are only within the RGB color space.
The applied rendering intent will remap the colors that are outside of the CMYK gamut to colors that can be printed within the CMYK color space.
With the Absolute rendering intent applied the colors are moved from outside the CMYK gamut to the nearest color within the CMYK gamut and the colors that fall within the CMYK gamut stay in their original position. This can result in a part where some of the colors may look slightly off and the remainder will look fine. (Depending on the colors selected there could be no noticeable change with this rendering intent applied.)
If we look at the Relative rendering profile we can see that all the colors move in a proportional manner inwards into the color space so this will result in a part that on its own looks very good and has the colors in proportion to each other however when one takes the printed part and compares it to a real life physical object containing some printed colors it may be obvious that all the colors are off.
For the most accurate colors we recommend using the Absolute profile however parts may look more cohesive with the Relative profile. As a result we recommend carrying out sample prints to determine which profile is most suitable to use for your application
Please leave a comment if you have any questions, we would love your feedback. If you found this helpful or interesting, check out part 2 on this topic.