Well, in a perfect world, the above would be true. However, we all know that nothing is perfect in this world and there are degrees to which perfection can be achieved. The reality is that the camera electronics can degrade the quality of an image captured by a CCD image sensor if it is not designed properly. The degree to which the camera’s electronics can accomplish the goal of preserving the fidelity of a captured image after readout from the image sensor is what distinguishes the cameras from manufacturers.
There are many different tests that can be run on a camera to determine various aspects of its imaging performance. Bias frame analysis is one of these tests. Bias frames are dark frames taken with the camera’s shortest exposure setting. Either the camera’s front is covered or its shutter is closed when taking a Bias frame. No light should have hit the camera’s image sensor during the Bias frame exposure. Analysis of a camera’s Bias frame is a good way of evaluating key parameters of a camera’s performance such as readout noise and pixel defects.
Below we have bias frames from four different brands of cameras that all use the same image sensor chip. In this case it is the KAI-04022 CCD chip from Kodak. As you can see there are a lot of differences between the images from the cameras. From this you can see that the above myth is disproved. If the myth was true, then all four Bias frames would look nearly identical since all four cameras use the same image sensor chip. |