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Pixels and Resolutions
Name: Herbert
Status: Educator
Age: 16
Location: N/A
Country: N/A
Date: Around 2001
Question:
Presently there is quite a bit of talk about pixels. Each
digital camera manufacrer claims there camera has 3 million pixels,
another 3.5 million, on and on. This reminds me of the 50's & 60's when
Hi-Fi audio manufacturers claimed there equipment had a wider bandwidth
than its competitor. So the question is what is the resolution of the
human eye, and can the figure be quoted in pixels?
Replies:
I will answer as much as I can, but your questions about the limits of the
human eye should really be directed to a specialist in the theoretical
limits of the human eye. Right now that is a question that has been
researched quite well, and there are several formulas to help predict that.
From what I understand, the resolution of the human eye is not measured
directly in pixels, but by the angular difference between two points of
light that can be resolved. Here is a very good article on that:
http://www.madsci.org/posts/archives/may97/864446241.Ph.r.html
From this article, if I have done the math right, I understand that a
typical person has a maximum resolution of about 17000 point sources per
inch. This doesn't really equate to pixels, but, pixels can be changed into
pixels per inch, and that should be close enough.
Digital cameras do brag about their resolution, because, well, it really
does matter. It matters because their resolution is so poor compared to a
real cameras, or a decent printer that it is pathetic.
For example, a really good digital camera might have a resolution of 2160 x
1440. If you made that into a 4x5 picture, you have a resolution of about
400 pixels per inch. Which isn't bad, but photo quality printers print at
2400 pixels per inch. If you decided to make it into a 8x10 photo, you end
up with about 200 pixels per inch. This was considered excellent quality 10
years ago, but is very poor quality by todays standards.
So, compared to the human eye, a real camera, or good printed material,
digital cameras aren't there yet. They do use a wide variety of software to
try and enhance the quality for printing, but there is still room for
improvement.
That doesn't mean digital cameras don't have a use. If you need pictures in
a digital form to be displayed on computer screens, then you have something.
A computer screen has a resolution of about 72 pixels per inch, and digital
cameras are definitely better than that. Also, since it is basically one
step from taking the picture to downloading it onto your computer, you get
better results than if you took a picture, developed it, and then scanned it
in, not to mention much faster results. With the popularity of the web,
digital cameras are great for creating images to place on a web site.
I hope this helps.
--Eric Tolman
http://www.madsci.org/posts/archives/may97/864446241.Ph.r.html
From this article, if I have done the math right, I understand that a
typical person has a maximum resolution of about 17000 point sources per
inch. This doesn't really equate to pixels, but, pixels can be changed
into pixels per inch, and that should be close enough.
It would seem to me that if the resolution of the human eye is one
arcminute at 10 inches, then the maximum resolution of the human eye is
found as follows:
You find the circumference of a circle of radius 10 inches, which comes to
62.83 inches. One 1/21600th (or 1/60th of a degree) of this is 0.002908
inches, the minimum possible perceptible distance by the human eye at 10
inches.
To get this much resolution, you need 343, not 17,000 pixels per inch.
Of course if you get even closer, the story changes, but what the
resolution of the human eye is at some other point that 10 inches I am not
sure.
Even taking a hypothetical one inch of distance with the exact same eye
resolution we still only get 3400 dpi, far short of 17,000.
Thanks,
-Josh Hug
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