"I'm waking up. After a rather bad night, at last I could sleep for a while. Control+S, save... damn, it doesn't work."

Horror tales

If time goes fast, it means you are doing nothing.

If time goes slow, you are doing much... but of no use.

Only if you look back a year, and you already lost the score of how many times you felt pride... there has been some use to your life.

JarFil

Many fiction tales have us delighted with slimy and "awful" monsters, born to the swamps, muddy pits and other places. Whay they haven't told us, and marketing tries to erase from our minds at all cost, is the fact that the first one dripping slimy beast, is the human being itself.

There's out on the ("civilized") world, an extended belief or way of thought most curious, which puts as on top of all the animals, calls us "superior beings", and believes in absolute cleanliness and tidiness. What a piece o bullshit.

The truth is that we're a bunch of slimy and dripping beings. All of us outpour liter after liter of sweat, saliva, mucus, feces, urine and wax through the ears. We are filled with sticky dirty blood stuck under pressure, lymph full of waste, stomach acids, bile, and a swarming wealth of bacterias int the intestines. If that was not enough, half the humanity drips vaginal secretions quite an amount of time each year.

We should look at ourselves from time to time, even if (specially if) we don't like whatever we see.

Of course, watching -civilized- extraterrestrials fleeing in dread and disgust at the mere sight of any of us, doesn't sell as much as making it the other way around. We humans must be the best ones, the most educated and civilized. Nobody likes to see how provincial, bad-mannered and awful one is, no matter how true that might be even according to his own opinion.

One of the basic questions when choosing a digital camera, deciding at what resolution would we like our photos, or how to pint them, is the one about "how many Mpx is a human eye able to see".

Well, first thing would be to tell you that Mpx are an abstract unit, translatable to plain surface units, while the eye "sees" in units of spheric vision angle. To join both units, we need one more: the distance from the eye.

For example, if at a given distance the smallest point an eye can see has a width of 1cm, at double that distance it would not see anything smaller than 2cm in width, while at half the original distance will be able to distinguish points of only 0.5cm.

Once that is said, let's suppose a "normal" distance: 30cm from the eye. When we look at a printed photo that's more or less the normal distance, while on a PC screen it's usually more like 60cm or more, and on a TV it rarely goes below the 200cm (2 meters).

So with just that, we already can see that on a TV we barely make out points 6.66 times wider than on a photo, which -taking into account we are talking about both width and height- means we will see 44 times less points than on a photo. If on a printed photo we would see 44Mpx, on a TV we wouldn't see even 1Mpx.

Now, let's take a look at the eye.

Insinde the ete there are about 100 millon light detectors (100Mpx), but they aren't distributed homogeneously; over 30Mpx are at the fovea, on an circular area of about 15º in diameter. But even there are they evenly distributed, and we are talking about 30Mpx "monochrome". A photo is taken in 3 colors (red, green, blu), so the equivalent of the fovea would be arout 10Mpx.

At the eye there is another severe limitation: the optic nerve, with barely 1 million fibers. Clearly, you can't match 100M detectors t 1M fibers, so the information that gets transmitted is "pre-processed" inside the ete. Border detection, contrasts, relative colors and others, it's all done in the eye befor it even reaches the nerve (which is the reason behind some optical illusions). In the end, only 1M impulses reach the brain from each eye, even when we need to provide the eye with a bigger amount of points so they get converted in the right impulses.

To compensat, we have two eyes (2M impulses) and both are trembling all the time to get more detail from where there is none. In a way, the mind is constantly interpolating low resolutions signals, using the fact that they come from sensors with a much higher resolution. In the end, the brain is quite capable to capture about 2Mpx for each position that is looks at.

But... and this is the "big BUT"... ¡we rarely look at the same point for a long time!

Usually we first watch one place, then another, then one more... an thus all the time, scanning each image at a pace of 2Mpx for each position. Defects due to blurry vision not accounted.

So, the end result would be more or less:

A human sees abouit 2Mpx for every 15º of visual field diameter.

Applied to a photo, the upper limit would be at about 2Mpx in a 8x7cm area at a distance of 30cm, or in other words:

• ~6Mpx on a 15x10cm photo at 30cm (~500dpi)
• ~5Mpx on a 17" TV at 2m
• ~4Mpx on a poster at 2m to 10m (~40dpi)

Luckily, to appreciate a given photograph there is no need to reach these maximum levels, and we well might do well enough with 4 or even 16 times less. Even if it turns out to be less realistic