Are the colors on your prints asking for a fix? Do the hues look brilliant on the screen, but the print—Mamma Mia! Conversely, do your colors scream instead of sing? Color plays an important role in our lives. It affects our moods and our pocketbooks, our appetites and our relationships. Since color is so significant to our everyday existence, knowing how to control it in our prints is essential.
The information in this article offers information and guidelines to help you achieve the best color relationships for your prints with a few commonly used tools and techniques.
Calibrate, Calibrate, Calibrate
If I’ve said it once, I’ve said it a thousand times: A calibrated workflow is the only way to get predictable color from your printer. The best way to calibrate your monitor is to purchase a colorimeter and measure the black, white and RGB values that the calibration software projects onto the screen. The software will produce a profile that your monitor will use to display images so that you can be confident that you are working in the best possible color environment.
Choose a Printer
For the best color images, a professional, large-format inkjet printer is a good choice. These devices usually can print up to eight colors and sometimes even more. They can be purchased in a variety of widths, from 13 inches to 72 inches, and even larger. Among the most popular printers are those made by Epson, Canon, H-P, Mimaki, Mutoh and Roland. They accept a huge variety of substrates in both sheet and roll form. Their ink-sets often contain two shades of cyan and magenta, one shade of yellow and two types of black, photo (for glossy prints) and matte.
Although inkjet printers use cyan, magenta, yellow and black ink, under no circumstances do you convert your images to CMYK mode. The raster image processor (RIP) that converts the RGB values of your pixels into the CMYK dot densities reconverts CMYK values back to RGB and then to CMYK potentially creating really weird color relationships. Convert RGB images to CMYK only when you plan to print color separations for offset lithography.
Use a spectrophotometer to scan a target image that has been printed by your printer on the substrate of your choice (see Figure 1). The target image contains swatches that describe the color capabilities of your printer and substrate and the spectrophotometer measures the wavelength and luminance of each swatch. If you don’t have a spectrophotometer choose one of the RGB ICC (International Color Consortium) profiles provided by the printer’s manufacturer that was loaded with the driver. You can access the profiles and assign them to the image in Photoshop’s Assign Profile dialog box (see Figure 2) found under the Edit menu (Check out the September, 2015 Digital Eye article, “Tips for Color Management”. It tells you how to follow these steps in more detail).
With a calibrated monitor, and a printer profile assigned to the image, what you see on screen is as close to the print as you can get … or is it? Usually when you assign the profile you’ll see color shift. Sometimes the shift will be minor, requiring a vibrancy or saturation enhancement. Sometimes the shift can be extreme.
Before adjusting color, it’s a good idea to duplicate the document so that you can compare the adjusted image to the original, side by side on the desktop. Granted, you can compare the images by looking at the default snapshot of the original in the History panel but that doesn’t allow for side-by-side comparisons, which I think is a better way to compare. Name the new document with the printer, substrate and date; for example: Epson11880 PremiumGlossyPhoto_12-01-15
It is usually a simple matter to enhance color, and there are countless ways to do it in Photoshop. The techniques you choose depend on the problems you need to correct.
For minor color shifts, the most direct color correction is a saturation adjustment. Saturation can suffer when the profile is applied as in Figure 3A. In this case I assigned an Epson StylusPro 4910 Archival Matte profile. Applying a saturation adjustment directly to the image can be destructive. Destructive is a term used to denote the non-reversible application of a process when the image is saved and closed. Sure, you can always reverse any step with the History panel, but why not attach the adjustment to its own non-destructive layer and have access to the settings with no fuss. If the Adjustments panel is not showing, choose Window>Adjustments. With both images visible on screen, choose the Hue/ Saturation (H/S) icon in the Adjustments panel. In the Properties panel (Figure 3B) drag the saturation slider all the way to the right. Woah! Too much!
Okay, now, drag it back until the image looks as close to the pre-profile original as possible as in Figure 3C. I also darkened it a bit with the Lightness slider. Compare this image to the original (Figure 3D). It may not be a perfect match because you’re looking at an image within the color gamut of the target printer and substrate. There are subtle variations in the color of the wigs and flesh tones of the mannequins, nevertheless, it’s a pretty close match and a vast improvement over the image prior to the adjustment.
In the Layers panel a Hue-Saturation Adjustment layer is generated that gives you the ability to go back at any time during the workflow and readjust the hue saturation and brightness (see Figure 4). Furthermore, the adjustment layer is accompanied by a layer mask that can mask off the correction where you don’t want it to appear.
Perfection is Elusive
In a perfect world a simple saturation adjustment is all you would have to do at the most to achieve perfect results. Unfortunately, more often than not a simple saturation adjustment is not enough. The image has acquired a radical color shift when a profile was assigned and needs further correction. I’ll address two of the most common problems that occur. First, the image's contrast has deteriorated, and secondly the image has acquired a significant color-cast as the example in Figure 5 shows.
In this case I applied an Epson Stylus Pro 11880 Premium Glossy Photo profile. These problems often occur together and can be stubborn to correct. Ideally, you will be able to correct both of these problems with one adjustment layer.
Adjusting Levels is a good approach to improving contrast and eliminating color-casts. Levels can work in sync with the Hue-Saturation adjustment you first performed, but for the time being, turn off the eye next to the HS adjustment layer to conceal the affect. Click on the Levels icon and if the image needs a contrast adjustment, drag the white Input slider to the left and the black slider to the right. Play with these sliders until the contrast is improved, then drag the gray midtone slider to the right to darken the image or to the left to lighten it (see Figure 6). Now click the eye next to the Hue Saturation layer to see the results and compare it to the un-profiled image. Make any additional adjustments to tweak the color.
Targeting a specific channel can help reduce color-casts. You can systematically eliminate red, green or blue casts and cyan, magenta and yellow casts. Oddly enough these colors are completely related and are adjustable in the Levels panel. Here is the theory behind this operation:
- If you have a blue cast, reduce blue by adding yellow. If you have a yellow cast, add blue.
- If you have a green cast reduce green by adding magenta. If you have a magenta cast add green.
- If you have a red cast reduce red by adding cyan, if you have a cyan cast add red.
Sound odd? Well maybe, but these colors are opposites on the RGB spectrum. To add a channel's color in the Levels panel, drag the white input slider to the left. To increase the color’s opposite, drag the black slider to the right. Then lighten or darken the color with the grey slider.
To eliminate a blue cast for example, expand the channels menu in the Levels panel and choose Blue. To eliminate blue, drag the black slider in the blue channel to the right. The image will begin to appear more yellow. Drag it until it is too yellow. Now, drag it to the left and stop dragging when color is balanced. You can adjust the red, green and blue channels this way until the image’s color is perfectly balanced when compared to the original un-profiled image. Figure 7 shows each color channel’s Levels adjustments applied to the profiled image.
To get even closer, I performed a final Curves adjustment on each of the color channels (see Figure 8A and Figure 8B). Curves enabled me to tweak the more stubborn areas and bring them closer to the original.
These techniques will help you recover from the shock color shifts that result from changing an image’s color profile. You can now see the image on-screen as closely as possible to how the image will look when the color is optimized and image is printed to your chosen substrate.