Can't see the screen in the sun? Blind by light at night? Let's tell you the secret of the human eye's light sensitivity, and why don't you use the brightness of the lighting effect to display the status. This article will take you through the nonlinear characteristics of the human eye and its impact on the interface design of smart devices.
This article will provide complete answers to the following questions:
- Why is it difficult to see clearly when the brightness of the mobile phone is the highest outdoors at noon?
- Why don't you turn on the lights late at night, and the brightness of the mobile phone is the lowest?
- What is Gamma?
- Why don't you use the brightness of the lighting effect to indicate the status?
These questions do not seem to be closely related, but they always revolve around the same knowledge point, that is, the principle of light sensitivity of the human eye. As designers, we often hear about hue, gradation, saturation, lightness... However, few people have studied the effect of light intensity on the human eye, and this article will tell you a new knowledge point, which is more suitable for students who have needs for hardware interaction design
1. The candlelight phenomenon of the human eye
Imagine a picture of lighting a candle in a completely sealed dark room, and if nothing else, this candle will be very conspicuous and become the focus of the roomIf you already have a hundred candles in front of you now, and the whole room is already bright, lighting another candle at this time may not determine how much the room is brighter.
Similarly, if we play with our phone in the middle of the night, even if the brightness is adjusted to the lowest, it will naturally feel very harsh; However, outdoors at noon during the day, even if the brightness of the mobile phone is adjusted to the maximum, it is natural to not be able to see the content of the screen clearly (the problem of screen reflection will not be discussed for the time being)
The above two phenomena are due to a basic photosensitivity principle of the human eye: the light sensitivity of the human eye is nonlinear, which is a very excellent property that organisms have evolved over tens of thousands of years.
This sensation can be described as the sensitivity of the human eye to light becomes weaker and weaker with the intensity of the light. There are many nonlinearities in the human senses, such as hearing, smell, etc.
Anthropologists speculate that this trait allowed our ancestors to spot suspicious beasts in the dark of night, and then not to be unable to tolerate the glare of the scorching sun during the day. It allows ancestors to survive in different environments.
2. Understand linearity and nonlinearity
Let's dive into linearity and nonlinearity.
I can use a DSLR camera to give people a better understanding of light sensitivity. How the camera simulates the human eye's perception of light:
Light passes through the lens into the image sensor CMOS, which is equivalent to light passing through the lens of the human eye into our retina.
The image sensor in the camera receives photons and converts them into charged particles, which then accumulate into voltage, and finally correspond to the gray value of the image. The more photons, the higher the brightness, and they are linear.
So the raw data taken by the camera is like this, the picture on the left, the reason why you haven't seen it is because the camera adds a layer of processing in order to make the photo closer to the human eye, and corrects it to the picture on the right. Similarly, the light received by the human eye should have been like the one shown on the left, but the long evolution has allowed humans to convert linear perception into nonlinear perception.
Human Eye Sensitivity = Light Intensity ^(1/x)
Linear to nonlinear only needs to be calculated once to the power of the power, where x is a variable, and for the human eye, this value is fixed at 2.2.
Such a correction relationship has to be gamma correction, and this x is the gamma value that we can adjust.
So what we usually talk about in the field of image and optics is gamma that is actually correcting that straight line into a curve.
Gamma correction is widely used in our daily life, such as the rendering adjustment just mentioned, PS common tools color levels, curves, and then display adjustment are all adjusting gamma, all of which are adjusting the relationship between linear and non-linear.
Finally, we are looking at two cases to further deepen everyone's understanding of photosensitivity.
The grayscale bar in Photoshop ranges from 0 to 255, and if you use absolutely accurate colors to represent this range, it will look like this:
This adjustment bar is not visually uniform, and that is because it needs to be absolutely evenly distributed, because our vision is not linear, so the vision looks uneven. A uniform gradient should look like this:
So Photoshop actually did a visual optimization, optimizing the expression of the computer's standard linearity into a nonlinear effect of the human eye.
3. Personal experience
I bought a cooking pot, probably like this, he has 2 gears, and he used the brightness of this light to represent the gear, when the bottom gear is a little darker, when the high gear is a little brighter.
This design has caused me a lot of trouble, because sometimes when I use it at night, even if I open it to resist, it looks very bright, and when I use it during the day, I still can't see it clearly.
Therefore, one of the principles that I have personally summarized is that in the design of lighting effects, we should avoid directly using the brightness of the lamp to convey information without contrast.
For the function of this level, the information can be conveyed by graphics, quantities, or hues.
For the function of this level, the information can be conveyed by graphics, quantities, or hues.
This article was originally published by @Kushim's on Everyone is a Product Manager. Reproduction without permission is prohibited.
Image from Unsplash, based on the CC0 license
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