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# Contrast Phenomena / Image Framing

[Laboratory]

A main objective of Image Processing is to help a user interpret an image. In order to seek this objective it is important to have some understanding of the Human Visual System (HVS). The HVS is responsible for transferring data into information by a viewer. It is interesting to note that perceived information may be represented by attributes such as brightness, color shades, and edges. It is known that a typical observer can discern from one to three dozen distinct levels of grey or intensity variations. If color is added, then a typical observer can discern thousands of color shades and intensities. In addition, most of the information is concentrated in the fine details, that is, abrupt changes or edges.

There is an interesting phenomena of the HVS that is called simultaneous contrast. It relates the perceived brightness of a region to its background. A region will become darker as the background becomes brighter and vice versa.

This phenomena can be visualized in the image shown below

Simultaneous contrast phenomenon

### Image Framing

The basic tool to create the image to illustrate the simuntaneous contrast phenomenon is the one which permits the addition of a frame around the image. In the figure below, on left is the original image and on its right, the same image was framed with a border o constant grey level value and constant width. The parameters of such tool are the desired output image size, the position of the original image in the output image and the grey level value for the frame.

a)original; b)framed image
a) | b)

### Buiding the Simultaneous Contrast Phenomenon Image

To build the image shown in the simultaneous contrast phenomenon, one can use the same tool used to frame the image in the last description to create each individual framed grey square and use the inset tool used in the lesson Comparing Images Visually to put the four grey boxes together.

- Lab: Contrast Phenomena / Image Framing