Everybody knows

There are many things that everybody knows, which nonetheless are not true.

More precisely, there are many questions you can ask of a hundred people at random, and they will all give the same answer, and that answer will be wrong.

To be fair, there are people who have no opinions about things. So let’s set some ground rules: A person can opt out of answering your question – they can just say “I don’t know”, or even “I don’t even understand what you’re talking about.” In that case, you can just ask somebody else your question, and keep on going from person to person until you’ve accumulated a hundred answers.

Here’s one such question: If you want to show the color black on a computer screen, you specify the color 0,0,0 (red and green and blue all zero). If you want show the color white on a computer screen, you specify the color 255,255,255 (red and green and blue all 255).

But what if you want middle gray, containing half the brightness of white? What color should you specify?

Just about anybody who chooses to answer this question will say something like 128,128,128 – and that’s a perfectly logical answer.

But it turns out to be wrong. The right answer turns out to be “it depends”.

In fact, on many computer monitors 128,128,128 will result in something considerably darker than half the brightness of full white. On my LCD screen of a Lenovo ThinkPad, half brightness occurs at around 170,170,176.

What I mean by that is that if you make a fine checkerboard pattern where half the pixels are black and the other half are white, and you compare this with a solid color, on my computer you need to set the solid color to around 170,170,176 to get the same overall visual brightness.

You’ll probably get somewhat different results on your computer monitor, but you can see the general idea for yourself. Look at the following image and squint, so that you can’t really see the details of the checkerboard. On my computer screen the solid gray areas look pretty close to the average shade of the checkerboard:

black/white checkboard versus 170,170,176


In contrast, on my computer 128,128,128 produces something waaaay too dark:

black/white checkboard versus 128,128,128


Of course, on your computer screen the second one might look right. The “correct” answer varies from screen to screen.

This means that lots of people who make images with computers are getting things very wrong. They think that to make something half as bright as white they always need to use 128, and to get a quarter as bright as white they need 64, and so forth. If you ever wonder why so many computer graphic images have an odd “fake” look, that’s one of the reasons.

Can anybody think of something else that “everybody knows”, where the conventional wisdom is wrong?

2 Responses to “Everybody knows”

  1. Ben Kanegson says:

    “Can anybody think of something else that “everybody knows”, where the conventional wisdom is wrong?”

    Here might be a few…

    “I live in an apartment. I can’t have a big dog.” Not so. In fact, medium sized dogs tend to be the athletes that require lots of outdoor exercise. Giant breeds tend to be lethargic. They can fit anywhere a person can.

    “South American countries are Hispanic”. Actually Brazil, the largest and most populous South American country, is Latin but not Hispanic. They speak Portuguese. Some in the US are aware of this but the vast majority are not. On our forms which offer check offs for ethnicity, we find options for Caucasian, African-American, Asian, Hispanic, and American Indian/Inuit. But many Brazilians find no appropriate label.

    “The US Government recently took over the 9 largest banks and bought into them for $25 billion each. A step toward socialism.” Well, each bank got $25 billion pretty much unconditionally, and they are using the capital for their own purposes, such as buying out smaller banks (which is contrary to the intent of anti-trust legislation and post depression financial regulations, which limited banks geographically and separated them by functional sector to create firewalls). So in the recent merger of government and banks, it is actually the largest banks which are taking over the government, not the other way around. A step toward fascism.

    Technically, the merger of banks and US Government actually happened with the creation of the Federal Reserve which is not federal and has no reserves (also contrary to conventional wisdom), but this latest action is a punctuation of the central bank’s power. The reason this is so pernicious is that the $225 billion they have created with a simple keystroke and granted to themselves will have to be repaid with the sweat and toil of all the working tax payers for at least a generation.


  2. sally says:

    the checkerboard hurts my eyes.

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