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Q: What does interpolation mean in regards to digital cameras? ( Answered 5 out of 5 stars,   1 Comment )
Subject: What does interpolation mean in regards to digital cameras?
Category: Miscellaneous
Asked by: mmo-ga
List Price: $5.00
Posted: 12 Oct 2004 10:11 PDT
Expires: 11 Nov 2004 09:11 PST
Question ID: 413722
When I'm reading descriptions of digital cameras for sale online I
have seen many references to the word interpolation, where the camera
might be advertised only 3 megapixels but it says you can get pictures
up to 6+ megapixels with interpolation, I don't understand what
'interpolation' means and would like to know more. Here's a quote from
one of the websites I was looking at: "Trendy Digital Camera with 3.2
Mega pixel and Continuous 4x Digital Zoom.  Image resolutions up to
6.4MP (interpolation)."

Also I don't understand much techical talk, I understand that I could
probably look up the definition somewhere and get it but I fear I
still won't 'get it' or understand the tech talk, so I knew I could
probably come to Google Answers again and find someone who understands
what this is about they could explain it to me in simple and easy to
understand laymans terms, thanks!
Subject: Re: What does interpolation mean in regards to digital cameras?
Answered By: aht-ga on 12 Oct 2004 12:51 PDT
Rated:5 out of 5 stars

You're right that there are a lot of technical definitions out there;
since you asked for a lay-person's description of what interpolation
really means, let me explain it in my own words instead.

We'll start with the digital camera primer from "How Stuff Works":

On this page (the 11th page of the primer), it briefly mentions that:
"This process of looking at the other pixels in the neighborhood of a
sensor and making an educated guess is called interpolation."

So how does it really work?

Well, think of the sensor in a digital camera as being like you
standing behind a screen-door (you know, the mesh kind), and looking
outside. Each square of the mesh represents one pixel. Each pixel has
a different value for color and brightness. All of the squares in the
mesh (ie. the entire screen door) combine to form the actual picture.

Remember that each square, or pixel, can only have one value for color
and one for brightness, though. So, if you took a smaller part of this
screen, and stretched it to double its size, with each square still
having only one color and one brightness, now all of a sudden your
picture is rather fuzzy and made up of these big squares. This is
where interpolation comes in. The computer in the camera looks at each
of these bigger squares, and tries to divide it into four smaller
squares. If it did this by just assigning each smaller square the same
color and brightness as the original bigger square, though, your
picture is still going to be fuzzy. So, what the computer does is it
steps back (figuratively speaking), and looks at what's going on in
the other big squares around the one it's trying to divide up. It
tries to smooth the color and brightness changes so that the end
result is that the whole picture looks smooth and less fuzzy.

The problem with interpolation, though, is that it is all just
guess-work by the computer. Since the value of each square is a single
color and brightness, what happens if there is a piece of detail that
happened to fall exactly between two of the original squares, and was
not captured by the camera? Well, that detail gets lost, since
interpolation can only guess at what "should be" between the original

Is interpolation only used in the situation you described? Actually,
no. All digital cameras use a form of interpolation to function. You
see, in the sensor in the camera, you actually have a grid of little
individual sensors, each capable of sensing only one of either red,
green, or blue. When you click the shutter, all of these sensors are
simultaneously exposed to "the picture" that you're trying to take.
Each sensor picks up a certain level of brightness in the color that
it can detect (red, green, blue). The computer then looks at the
entire grid of sensors and their values, and calculates what the value
of each pixel (the squares in our screen-door example) should be. This
can get very complex right away, so I won't go into any deeper level
of detail than this; just remember that this is a form of
interpolation used just to figure out what color and brightness each
pixel should already have in the first place.

Also, you'll have seen that some digital cameras have optical zoom,
some have 'digital zoom', and some have a combination of the two.
Optical zoom is exactly that; the optical lenses in the camera are
used to zoom into the picture before the picture ever reaches the
sensors, so as far as the sensors are concerned, it's like you walked
closer to the picture itself. With digital zoom, though, it's all
interpolation. When you ask the camera to zoom in, it simply stretches
out a smaller portion of the 'big picture', and then makes educated
guesses to try to fill in the details between the original pixels.

Does this explanation help? If there is any part of this that is still
'fuzzy' to you, please let me know using the Request Clarification
button above!


Google Answers Researcher

Clarification of Answer by aht-ga on 13 Oct 2004 09:04 PDT

I'm glad that you found the description useful, and thank you for the tip!


Google Answers Researcher
mmo-ga rated this answer:5 out of 5 stars and gave an additional tip of: $2.00
That was a really fantastic explanation, thanks so much for taking the
time to explain it to me in a way that I would understand.


Subject: Re: What does interpolation mean in regards to digital cameras?
From: pinkfreud-ga on 12 Oct 2004 13:04 PDT
What a great answer! 

I have a background as a computer graphics artist, and the concept of
interpolation is one about which I've been asked by friends and
relatives. I always tend to get too technical in trying to explain.
The next time someone asks, I'm going to refer them to aht's answer.

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