Color Depth (65k, 262k, 16.7M colors)

Color depth is the number of colors that can be used for each pixel on the display. This can range from 8- bit color, 16-bit high color to 24-bit true color. The range of color is determined by how many bits of red, green and blue (RGB) each pixel is assigned to the frame buffer.

A pixel’s color value is measured in bits-per-pixel or bpp. These colors are then color mapped from the signals in a variety of combinations. Memory, frame buffering, and bandwidth can be trade off’s for higher color depth and should be considered when choosing color depth of the display. Below are some typical color depths and their characteristics.

Figure 1: Color Depth (65k, 262k, 16.7M colors)-1

A 16-bit color depth known as “High color” can contain 5 red bpp, 6 green bpp, and 5 blue bpp. This is also referred to as RGB-565. Alternatively, the 16-bit color depth can assign RGB-555 with one unused bit. The RGB-565 color depth will result in a range of 65k different colors. (25+ 26 + 25 = 216 = 65.5k colors).

These 16-bit RGB values are typically transmitted as hexadecimal values ranging from black RGB (0,0,0) = 0x0000 (no color) to white RGB(1,1,1) = 0xFFFF (all colors) and everything in between. Below are definitions for a variety of 16-bit colors.

Figure 2: Color Depth (65k, 262k, 16.7M colors)-2

The RGB data is stored in the frame buffer which is memory allocated in RAM to periodically refresh the display. Higher color depth (higher bpp) means that more memory will need to be used to display the image. The frame buffer memory needed is the total number of bits or bytes for one frame. This is calculated as pixel area x number of bits/pixel.

For example: a 240×320 resolution display using 16-bit color will require a minimum of

Figure 3: Color Depth (65k, 262k, 16.7M colors)-3

153.6 kB of memory allocated per frame. This can result in a large portion of memory being used depending on the size of the display and the color depth chosen.

The size of the frame buffer and how often it is refreshed is called the bandwidth. Typically displays will have a refresh rate of 60Hz, this results in a bandwidth of (153.6kB x 60Hz) 9.2 MB/second. Larger displays with higher color depth would need a controller capable of higher speeds and memory storage.

Figure 4: Color Depth (65k, 262k, 16.7M colors)-4 & 5

The difference in picture quality between 6bpp (262k colors) and 8bpp (16.7M colors) is very minimal as it pertains to visible color range. Unless using the display for very high precision graphics it may be a good option to opt for a lower bpp ratio to conserve memory and optimize the speed of your device.

DISCLAIMER

Buyers and others who are developing systems that incorporate FocusLCDs products (collectively, “Designers”) understand and agree that Designers remain responsible for using their independent analysis, evaluation and judgment in designing their applications and that Designers have full and exclusive responsibility to assure the safety of Designers’ applications and compliance of their applications (and of all FocusLCDs products used in or for Designers’ applications) with all applicable regulations, laws and other applicable requirements.

Designer represents that, with respect to their applications, Designer has all the necessary expertise to create and implement safeguards that:

(1) anticipate dangerous consequences of failures

(2) monitor failures and their consequences, and

(3) lessen the likelihood of failures that might cause harm and take appropriate actions.

Designer agrees that prior to using or distributing any applications that include FocusLCDs products, Designer will thoroughly test such applications and the functionality of such FocusLCDs products as used in such applications.