Synthetic Images
Camera Bit Depth
The bit depth relates to the number of light intensity values a single pixel may take. In a digital camera, each CCD sensor stores a number, which indicates the amount of light that contacted it while the sensor was exposed. Due to the limitations of computers, these numbers are limited by the amount of bits which describe each sensor reading, or the value of a pixel. To understand bit depth, we must first recognize that current computers may store only ones and zeros. The number of ones and zeros per sensor output (bits) determines bit depth. In other words, bit depth describes the number of values each pixel may take. If the image has bit depth of one, the image may take two values: 0 or 1. However, if an image has a bit depth of 2, four different values may be stored: 00, 01, 10, 11. Similarly, if an image has a bit depth of 3, eight different values may be stored: 000, 001, 010, 011, 100, 101, 110, and 111. This pattern continues where the number of values each pixel may take is described as:
Most PIV setups use (original or converted) black and white images as they allow more information about the amount of light to be recorded. As a result, we will focus on black and white images. Figure 1 demonstrates the effect of bit depth (number of bits in parentheses) on a single particle image.
Figure 1. Demonstration of the effect of bit depth on a single particle image (particle image diameter of 10 pixels). As shown, a greater bit-depth allows researchers to gather more information. This added information adds to the quality of PIV correlations.
Author: Jack Elliott
Date Published: June, 2022