Why can't you print RGB?

RGB (Red, Green, Blue) is not suitable for printing because it is based on the additive color model, which is used for light, not pigments or dyes. Here's why you can't print directly with RGB and what makes printing different:

1. Additive vs. Subtractive Color Models

• RGB (Additive Color Model): RGB is used for light-based displays, where colors are created by adding different intensities of red, green, and blue light. The more light you add, the closer you get to white, which is the combination of all three colors at full intensity.
• CMYK (Subtractive Color Model): Printing, on the other hand, uses the subtractive color model (CMYK - Cyan, Magenta, Yellow, and Key/Black). In this model, colors are created by subtracting light using pigments. When you mix pigments, they absorb certain wavelengths of light and reflect others. The more colors you mix, the darker the result gets, which is why you need black ink to achieve full richness in colors.

2. Why RGB Doesn’t Work for Printing

• RGB works with light: Screens (like monitors, TVs, and smartphones) emit light, so they rely on the RGB model to mix and display colors. When you use RGB, the screen emits light directly to your eyes, and mixing red, green, and blue light creates the entire color spectrum.
• Printing relies on pigments: Printers use inks or toners, which absorb (subtract) specific wavelengths of light to create colors. CMYK is specifically designed for this purpose because it works by subtracting wavelengths from white light.

3. Color Gamut Differences

• RGB has a broader color gamut: RGB can display a wider range of colors than printers can reproduce because it works with the full spectrum of light.
• CMYK has a more limited color range: Printers can’t reproduce all the colors that RGB displays. Some colors, especially bright or neon colors, are outside the printable range (gamut) of CMYK.

4. The Process of Conversion

When you want to print something that was created in RGB (such as on your computer screen), you need to convert the image to the CMYK color space before printing. This process ensures that the colors are represented accurately within the limits of what can be printed.

• Software like Adobe Photoshop can perform this conversion, but the final print may look different from what you see on the screen because of the difference in color models and gamuts.

5. Color Accuracy and Print Proofing

To achieve the best print results, color proofing is required to adjust the RGB image for printing. A printer will often produce a soft proof (a simulated version of the print) on the screen so that you can adjust the colors before final printing.

Conclusion:

You can't print directly with RGB because RGB is based on the additive color model used for light, while printing relies on the subtractive color model (CMYK) that uses pigments. RGB is great for digital displays, but to print an image, it must be converted to CMYK to match the limitations and characteristics of physical pigments. This difference in color models explains why printed colors can appear different from what you see on screen.