Despite a good deal of confusion – and unfortunately, misrepresentation – in the digital signage industry, bit depth is actually an important metric for purchasers, advertisers, and content creators to consider.
Bit depth, sometimes referred to as color depth or color capacity, can be a very technical, in-the-weeds concept. We’ll keep it fairly simple here and describe the basics so you can better understand the term.
Bits Are Binary Values
A bit refers to a binary value (0 or 1), or simply off or on. For example, a normal light switch is binary, but a dimmable light switch has multiple levels.
For imagery, one bit is black and white (no shades of gray). Two-bit expands to four total shades (white, black, white-gray, and black-gray). Each additional bit doubles the number of shades from before. Two more bits, for example, quadruples the number of color levels.
The Bit Color Chart in Figure 1 shows how color levels increase exponentially with each added bit.
FIGURE 1 – BIT COLOR CHART
Additive Color vs Subtractive Color
Additive color (used in displays) is different than subtractive color (used in printing). If you’ve ever bought ink cartridges for your printer, you will be familiar with the CMYK colors – cyan, magenta, yellow, and key (black). These are the literal opposites of RGB colors – red, green, and blue.
In additive color, red and blue make magenta. Blue and green make cyan. Green and red make yellow. Equal parts RGB make white. Subtractive color flips this, as magenta and yellow make red, cyan and yellow make green, and magenta and cyan make blue. Equal parts CMY makes black. This might not be intuitive, but it is absolutely true. Consider this: when a display is showing RGB as 255/255/255, it shows white. When the display is off, it’s black. If you’re printing, the paper alone is white and putting equal parts CMY on the same spot will make it black, in theory. (In reality, it’s brownish due to pigment quality.)
But what do these color calculations have to do with bit depth and digital displays, you ask?
Bit Depth and LED Displays
An LED display is generally built with red, green, and blue diodes. Each of these channels is capable of multiple shades (depending on bit level), which creates a wide spectrum of available colors.
But what if each channel had only one bit of control, on or off? Simply put, this wouldn’t be very effective. It would allow for just eight colors (red, green, blue, cyan, magenta, yellow, white, and black) for each pixel. As you can imagine, this would be a very rudimentary display. The good news is that except for some extremely basic informational displays, virtually all digital signage today outperforms these basic color levels.
Bit depth for color is expressed as either bits per component, channel, or color. All three share the abbreviation “bpc” and are interchangeable. It’s confusing, but unfortunately the industry standard.
If each channel has four bits of control, the total number of color levels per channel is 16 (24). Therefore, the color capacity of the display is 4,016 colors (16 x 16 x 16).
Is More Better?
By logical extension, more bits would be better, right? Yes, but only to a point. Many LED displays are eight-bit per channel (24-bit total), which generates about 16.7 million total colors (256 x 256 x 256).
However, according to David G. Myers in his 1995 book Psychology, the typical human eye can discern about 7 to 10 million shades of color. Thus, more than 16 million should be plenty. This is why 8- to 12-bit color is the standard for LED displays, TVs, computers, and a host of other displays.