Changing Brightness in an Image: Continuing with a Visual Illusion Experiment – Part 4

In this video, i’ve adapted the previous video by altering brightness to see what effect this has (if any) on the illusions. The video is best viewed full screen. My findings which the reader can check are that

1. If the image is very bright or very dark one of the effects is lost – the apparent leaching of colour onto the lighter side of the circle. To see this effect you will need to look closely at the circle moving in the upper right screen. The left side of the circle is slightly lighter and when the circle moves to the left it becomes momentarily darker. Since the circle must remain invariant throughout (including the shading) this effect represents an illusion.

2. There was a slight ‘shimmering’ of the circumference of the dark circle (lower left). The circumference consists of alternating white and black segments which is supposed to produce a weak movement effect when the circle is stationary. Perhaps this is not the best video demonstration and I may need to reproduce this as a single video (1 circle as opposed to 4) so as to show this effect more readily.

By altering the brightness of the circle videos I generated two hypotheses

1. The alternating black/white circumference is more likely to show a movement effect if the circle is darker in colour. This probably maximises the contrast at the circle boundary.

2. There colour leaching effect is dependent on a minimum number of graded colour shades to achieve this effect. When the brightness is increased or reduced there are effectively less shades of grey (which also results from the resolution and colour properties of the image) and the leaching effect is lost. A secondary hypothesis might be that the likelihood of this effect is directly proportional to the number of colour shades in the image although this would obviously require further testing.

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