About Color Gamut
More often than not, when printing to the color printers we are asked, "Why didn't the color on my print out come out like the color on the computer screen?" Or, "How come the scanner didn't pick up all the colors in my photograph?"
Ahh...The Mystery of Color
When working with digital images, we use color models to describe these colors. There are a number of them: RGB, CMYK, Lab, etc., and each of them uses a different way of describing colors. In the various color models, there are color options known as color spaces. For instance, RGB, contains sRGB, Adobe RGB, Apple RGB, etc. The CMYK model also has various color spaces to work in. These spaces have a limited range of reproducible colors. This range of colors is known as gamut.
The various devices work within their own limited color gamut. Not one of them can reproduce the total range of colors seen by the human eye. To make things even worse, no two devices have the same color space. Although they all use RGB to define color, they interpret it differently.
When using Photoshop (or other image-producing software), image color values are actually being adjusting numerically. These numerical values are not really colors at all. They only have a very localized color meaning in the color space (gamut) of the device that is reproducing the color.
So whenever your image is moved from one device space to another device with a different color space (i.e., scanner-> monitor-> printer), which can only reproduce colors in its gamut, the image colors will change (i.e., pretty blue on screen, dark purple in print). The color change happens because each device has mathematically interpreted the RGB or CMYK values according to its own color space (gamut).
Because each device has a different color space, it’s impossible for all the colors you see on your monitor (RGB color space) to match the output from your desktop printer (CMYK color space). Their gamuts are different.
While color monitors are only capable of displaying certain parts of the visible color spectrum, color dye pigments used in the printing process are capable of reproducing even fewer of those colors.
Additionally, some of the colors produced by inks cannot be displayed on a monitor, and some colors displayed on a monitor are not reproducible using inks on paper. And on top off all that, different monitors can display the same image very differently.
What can you do to fix this problem?
Even though it’s impossible to match all colors on all devices, using a color management system is one good way to help achieve something close to consistent and predictable color between devices. Luckily Photoshop has a very good color management system built into it. The following is a list of basic steps that you can do to help ensure what you see on the screen is what you get in your print (WYSIWYP).
1. Calibrate your monitor using the Adobe software included in Photoshop, Apple’s monitor calibration software, or third-party equipment and software.
If well-matched printed output is your main objective, this change is really important. This is one of the most over looked settings by the majority of Photoshop users. By default, this setting is set to the much more limited sRGB space used for web-based images. This setting can be changed in all Adobe products, so your images will appear the same throughout your workflow.
3. Be sure you install the proper software that comes with your printer or download and install the software for other printers you print to. This software installs drivers that tell your software how to convert your monitor color space to that particular printer’s color space. Remember, all printer spaces are not the same! They are all very different and using the right one will make a huge difference in your final image.
4. In addition to the driver software, you will generally get paper profiles as well. All paper is not alike. Each manufacturer produces different varieties, which have their own type of white (some are yellowish, some grayish, etc.).
Also you need to consider paper surfaces. Different surfaces can dramatically change the way colors appear in a print because of the way they accept or absorb color. Some surfaces are capable of displaying more color than others. For instance, glossy surface paper displays a different range of color than a matte paper can.
These profiles will generally be for the papers that the printer manufacturer recommends using in that particular printer. They are usually made by that particular printer's manufacturer (e.g., Epson, Canon, HP, etc.). In general, these profiles are the best ones to use, because their inks and papers are made to work together and there are many stability issues (e.g., waterproof, longevity, etc.) to consider before changing paper products. That said:
5. When using third party art papers, ALWAYS download or ask your paper supplier for their paper profiles. Most of the art paper makers have profiles made for all the most popular photo printers.
NOTE: If you send your files to a professional CMYK production printer, ask them for their drivers and paper profiles.
In general, you will be working in RGB throughout the printing process. While color printers inks are actually CMYK, they are expecting RGB images to come through them. The conversion takes place in the printer and your software. Sometimes when working on images that will be sent to a publisher, you will need to convert your image to the limited CMYK gamut. You can preview any color changes using Soft Proof in CMYK mode and turning on Gamut Warning. All of these options are available in the View Menu. Instructions for doing this follow.
It is extremely important to remember that any gamut changes you make to the image will be applied for the chosen proof space only, and it is permanent! You will always want to edit your image on screen in RGB and save it. Use a duplicate of the original image for gamut correction, and save with the proof type attached to the duplicates name should you wish to print the file again on that printer with that paper. (for example, Filename-CMYK.psd).
NEVER make this type of gamut correction on your corrected original. Remember all gamuts are not the same. What is out of gamut in one profile is within gamut on another.
Some Tricks For Fixing Bad Gamuts
Most of the color imaging software available today will give you a warning when your colors or a specific color is out of gamut. If you suspect a color to be a problem, many graphics programs will have a way to indicate that it is. In Photoshop you can use Gamut Warning in a number of ways to adjust problem areas.
In Photoshop you can sample the questionable color with the Eyedropper tool. This option works best if the image contains only small areas of problem colors.
If large areas of color need adjustment, the problem areas of color can then be selected and adjusted.
First find all the problem areas in your image.
1. Under the menu item View -> Select a Proof Setup,
2. Under the menu item View -> Select gamut warning.
Once the problem area is located, there are a couple of ways to bring the problem areas into the chosen proof gamut.
A very basic option
1. Select the Sponge tool. It’s grouped with the Dodge and Burn tool icons in the toolbar.
2. Select the smallest brush size for the problem area. Set the pressure setting to a low number (in the Tool options bar).
3. Mouse over the problem spots with the Sponge tool, and it will replace the unprintable color with one close to the color but printable (in Gamut).
For detailed and illustrated instructions on this process, please see the Photoshop Sponge Tool Gamut Correction pages.
A more advanced option: The Hue and Saturation option
1. Select your profile and turn on Gamut warning.
2. Add a new Hue and Saturation Adjustment Layer from the layers window.
3. Use the drop-down options to select the predominate offending color to adjust.
4. Use the add to sample eyedropper and drag it over the out-of-gamut regions in the image (covered in gray).
5. Move the Saturation slider to the left to decrease the selected areas of saturation.
Repeat the process if you have other colors in your image that are out of gamut.
Note: By using an Adjustment Layer instead of the menu command, you are making a change that can be removed or adjusted at any time. You can create an adjustment layer like this in a single image for all your most used profiles. Just name each layer with the profile name, so you know which to turn on and off as needed. Since these layers do not add to your image file size, it is a better option than having many files with similar names taking up hard drive space.
For detailed and illustrated instructions on this process, please see Gamut Correction with Hue and Saturation.
Using Color Range and CMYK Out of Gamut
If you are using a professional printer, you can find and select all the CMYK out-of-Gamut colors at once using the Color Range command in the Select menu item. Remember that this option will select the working CMYK range, which is determined by your selected option in the preferences. Your selection may not be the same CMYK environment that your professional printer uses. So as always, when working with a professional printer, talk with them to find out what they are using, make a copy of your image, and edit it according to their recommendations using soft proof.
1. Open your image in Photoshop.
2. In the View menu -> choose Soft Proof -> select your CMYK profile.
3. In the Select Menu -> choose Color Range -> the Dialog box appears.
4. In the drop-down box -> choose Out of Gamut -> OK.
5. When the Dialog box disappears, all the out-of-gamut colors are selected. Use the Hue and Saturation method above to make corrections.
If you are wondering if it is collecting all the colors, you can turn on gamut warning as well, and you will see that it does collect the range.
NOTE: This quick Color Range trick only works with the CMYK gamut. If you use this option while soft proofing in another profile (like Epson or Canon paper profiles), it will not work. It will always select the CMYK gamut set up in the working CMYK profile.
Prints Too Dark
How to Change the Gamut Warning Color
The default gamut warning color is set to gray. This setting works well for most color images. I have included the instructions in case you need or want to change it.
1. Choose Photoshop > Preferences > Transparency & Gamut.
2. Under Gamut Warning, click the color box to activate the Color Picker.
3. Pick a new warning color, and then click OK.
4. If you want to change the opacity of the warning color you can change the Opacity value in text box. It can range from 0 to 100%.
5. Click OK.
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