Why is the blue river water green

Started Sep 30, 2020 | Questions thread
rc53 Contributing Member • Posts: 607
Re: Why is the blue river water green

Charles2 wrote:

ld_bl wrote:

It looks to me like the surface of the water is simply reflecting the green foliage above the water line at that angle.

Agree - and it shows the difference between how a sensor sees and how our eyes see. The latter go to a brain that "sees" there is a reflection, subtracts it, and discovers the real color blue of the water.

Less common than the case when the eye and brain see the color of an object by subtracting the cast of nonwhite light shining on it. The camera sensor does not do that.


There is no problem with the camera. Our brain "knows" that the water should be blue, and we "see" it as blue. The camera sees is as "green".

This is a perceptual problem; a common example is when trying to photograph a bride in the shade, or on grass. Her white dress will be illuminated by reflected bluish light from the shadow, or green light from the grass. But we "know" her dress is white. Seeing the print later we don't have this "frame of reference", and our brains don't alter the colour of the dress, or in this example, the colour of the river.

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