11.1 Image Interpretability in the Imaging Chain
Once the image is processed and displayed, it is ready for viewing. Understanding how the image will be viewed and interpreted is the final stage of the imaging chain, but this knowledge influences the design of the other imaging chain elements. Our focus here is the visual interpretation of an image by a human, but the interpretation may also be performed by a computer. For example, the intended use of the image may be for automated detection algorithms and not for viewing at all, in which case the optimal design of the imaging chain will probably be different than one designed for viewing the images.
11.2 The Human Visual System
To better understand how image information is interpreted by the viewer, we need to understand the human visual system (HVS). The HVS can be treated as another imaging chain (Fig. 11.2), starting with the radiometry from the image display, then substituting the eye for the camera, the brain for the image processor, and the cognitive visualization of the image for the display.
The pupil of the eye acts as the aperture of the camera; thus, the OTF for the eye can be modeled as a Gaussian function that is dependent on the pupil size,1 i.e.,