Digital Photography Live

Understanding Bit depth

We have heard of the terms bit depth and resolution and even megapixels. Often people use them interchangeably. This is wrong as they although related to the effective resolution of the camera system, are different in their inherent meanings. Let’s take one of them, bit-depth and have a deeper look into what it is.

Digital photography is all about numbers representing different shades of color. In the earlier days of black and white digital photography, processing systems embedded in computers and powering the overall image processing could only play around with 1 or 0 (two numbers). These were essentially 1 bit computer systems which could produce only 1 number at a time. These were assigned to black and white and each pixel thus could have only one of 2 possible tonal shades. Gradually as computer systems and along with that processing engines improved, 2 bit 3 bit and gradually 8 bit image processing systems became a reality. A 2 bit processing engine could represent 4 shades represented by the numbers 00, 01, 10, and 11. A 8 bit processing system could create a image file that has 256 combinations or colors (2 x 2 x 2 x 2 x 2 x 2 x 2 x2). In order to represent a picture that has the optimum number of colors in it (which is required to create a picture with no color jerks) is 250. As such an 8 bit image processing system is the basic requirement for color digital photography.

We also need to understand that at the heart of the image processing system is the camera sensor. This is that one element of the camera which has light sensitive photodiodes and which captures the reflected light from the subject. Now each photodiode is like a chamber which captures the light. However these chambers are not designed to capture all the light waves. Only three primary colors, red, blue and green are captured. We have discussed about Bayer Pattern elsewhere on this website. It is the most common forms of filter patterns that is used in modern digital camera sensors. It captures more of the green light then the other two primary colors due to the fact that the human eye is more susceptible to the green color.

A RAW file shot using an 8 bit image processing system has all the information to be able to convert it into a 24 bit image using a photo editing software. What it basically means is that each of the primary channels (or color channels) can capture 256 shades and thus has the potential to be converted into a 24 bit (8 x 8 x 8) image after post processing.

Modern digital camera technology has not stopped at 8 bit though. Camera manufactures have been churning out equipments which have still higher resolution of 12 bit and 14 bit. This means during post processing a photographer has a lot of tonal information in the image (if it has been shot in RAW). These are however heaver in file size and can easily overrun the buffer of the camera during shooting and also the memory card if one has to do a long shoot. Shooting RAW is thus advantageous when the photographer wants to preserve the full information that is captured so that he can produce the best quality pictures during post production and publishing.