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RGB and CMYK
RGB and CMYK are two fundamental color models used in various applications, from digital displays to printing. Understanding the differences between them is crucial for anyone working with visuals.

Colour Gamut: What is it?

In order to better understand colours, you need to know what a colour gamut is.  Basically, a color gamut refers to the range of colours that can be accurately represented by a device such as monitors and printers.  It is the colours that the output device can produce.  Devices with a larger gamut, such as monitors, can produce much more colours than devices with a smaller gamut, such as printers.  Each device will have it's own unique colour gamut and as such represents colors slightly (or even dramatically) different.

RGB (Red, Green, Blue): The colours of light

RGB is an additive colour model.  This means that colours are created by adding different intensities of red, green and blue light together.  When all three colors are combined at their full intensity, they produce white light.  When all are absent, you get black.

Think of it like this:

  • Your computer monitor, TV and smartphone screen all use RGB.  Each tiny pixel on your screen contains sub-pixels that emit red, green and blue light.  By varying brightness of these sub-pixels, millions of different colours can be displayed.
  • Stage lighting often utilizes RGB.  By mixing different colored spotlights, lighting designers can create a vast spectrum of hues on stage.

Key characteristics of RGB

  • Additive: Colours are formed by adding light
  • Used for digital displays: Screens, cameras, scanners
  • Produces a wider gamut of vibrant colors: Especially bright greens and blues
  • Color values range from 0 to 255 for each channel: Pure red, for example, is 255 red, 0 green, 0 blue

CMYK (Cyan, Magenta, Yellow, Key/Black): The Colours of Pigment

CMYK is a subtractive color model.  This means that colors are created by subtracting (absorbing) light.  When light hits an object, certain wavelengths are absorbed by the pigments and others are reflected.  The reflected wavelengths are what we perceive as color. In CMYK, the inks absorb different parts of the visible spectrum.

Why "K" for black?

While theoretically combining 100% cyan, magenta and yellow ink should produce black, in practice, it often results in a muddy brown.  This is due to impurities in the inks.  Therefore, a separate black (Key) ink is added to achieve true blacks, provide richer shadows, and reduce the amount of coloured ink needed for darker tones, which saves costs and allows for finer details.

Think of it like this:

  • Your home printer uses CMYK ink cartridges.  When you print a document or a photo, the printer lays down tiny dots of cyan, magenta, yellow and black ink
  • Commercial printing presses also rely on CMYK.  Magazines, brochures, billboards - all are printed using these four inks.

Key characteristics of CMYK

  • Subtractive: Colours are formed by subtracting light (absorbing certain wavelengths)
  • Used for printing: Printers, presses, anything with ink on a physical surface
  • Produces a narrower gamut of colours compared to RGB: Especially for very bright or neon shades
  • Color values are expressed as percentages: Pure cyan, for example, is 100% cyan, 0% magenta, 0% yellow, 0% black

When to use which

The choice between RGB and CMYK is determined by your final output

For anything that will be displayed on a screen

For outputs such as websites, digital art, social media graphics, videos etc, use RGB. Designing in CMYK for screen display will result in duller, less vibrant colours

For anything that will be printed

Brochures, business cards, posters, t-shirts, documents etc. should be designed using CMYK. Designing in RGB for print outputs can lead to unexpected color shifts and less accurate representation of your vision once printed.  Printers simply cannot reproduce the full spectrum of RGB colors.

The conversion challenge

Converting between RGB and CMYK is not always straightforward.  When you convert an RGB image to CMYK, some colours that exist in the RGB gamut (like very bright greens or blues) may not be reproducible in CMYK.  This is known as "out-of-gamut" colors, and they will be shifted to the closest CMYK color in the gamut.  This will result in a noticeable color shift, and may even produce a completely different color.

Tips for a smoother workflow

Start in the correct color mode

If you know your final output will be print, it's often best to design directly in CMYK from the beginning, or at least be aware of potential color shifts.

Soft proofing

Many design software programs offer a "soft proofing" feature that simulates how your RGB design will look when converting to CMYK.  This allows you to make adjustments before printing.

Use pantone colors for critical branding

If color accuracy is paramount for your brand (e.g., a specific logo colour), consider using Pantone (spot) colors, which are pre-mixed inks that offer consistent color reproduction across different printing methods.

In conclusion

Understanding the fundamental differences between RGB and CMYK is essential for achieving accurate and vibrant colours in all your visual projects, whether they live on a screen or in print.  By choosing the right color model for the right application, you can ensure your colors always look their best.

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