How does a digital camera work - Part 4

Note: Please forgive the long hiatus between blog posts. Much has transpired, including a bout of Lyme Disease that took me off the grid for quite a while. I am back, planning a new adventure, and will be posting on a more regular tempo again. Thanks to all who have been ever so patient.

 In Part 1 we saw how millions of tiny bits of silver can make up an image. In Part 2 we explored color filters and their role in seeing some things and not others. Part 3 showed how light levels could be converted into proportional electrical energy.

The scenic information created by the photo sensor we created had two major problems. It lacked relevance and persistence. My friend could point the sensor wherever she wanted and could create a picture of the scene before her in her mind. However, she could never be sure she was pointing at the same spot twice in a row with much precision. One spot had very imprecise relevance to any other spot.

Additionally, even if a perfect picture could be constructed it was only as good as her memory. As they say, "Out of sight, out of mind!"

Let's see if we can fix both of these problems, relevance first. When a movie wants to show the view through a telescope or periscope it shows a black screen with a circle of light in the middle.

What if we lined up 10 rows of 10 tiny telescopes in a 10x10 grid? We would carefully align them in parallel to cover areas that conjoin one another. We would then put a light sensor behind each one of them. The result would be a real picture like the one we imagined before but with circles instead of squares.

spac	spac	spac	spac	spac	spac	spac	spac	spac	spac
.	.	.	.	.	.	.	.	.	.
.	.	.	.	.	.	.	.	.	.
.	.	.	.	.	.	.	.	.	.
.	.	.	.	.	.	.	.	.	.
.	.	.	.	.	.	.	.	.	.
.	.	.	.	.	.	.	.	.	.
.	.	.	.	.	.	.	.	.	.
.	.	.	.	.	.	.	.	.	.
.	.	.	.	.	.	.	.	.	.

Now my friend can see the tree, a cloud, and a stream in a meadow! We have achieved relevance!

This is a major advance but let's face it, one of the great assets of photography is the ability to look at an old picture we took in the past. Whether it's the old photo album you have on the shelf or a picture gallery on your phone the whole purpose of taking a picture is to preserve the moment.

Let's start by calling each square/circle a picture element to give it a common name. In fact, we could shorten picture element to pixel to make it easier to remember and for me to type. Now let's number each pixel from 1 to 100 startling in the upper left and ending in the lower right. All that's left to do is to get a note pad and write down the value of each pixel from 0 - black to 5 - white in the picture above.

1..17   - 4
18      - 5
19..23  - 4
24      - 1
25..26  - 4
27..29  - 5
30      - 4
...
91..94  - 3
95..96  - 2
97..100 - 2

and on and on - I'm sure you get the idea.

Any time I wanted to recreate this picture all I would have to do would be to get out my note pad and color in the squares/pixels according to the values I had written down previously. Thus we have attained persistence.

Believe it or not, this is all that a digital camera does. It has a grid of sensors that register light and write the values to the memory chip. When you want to see the picture you camera or computer goes to the chip and reads the values and displays them on the screen.

Because a digital camera is nothing but a computer with a lens it can do these things very fast. Since the sensors are microscopically small there can be millions of them. Mega (millions) Pixels (picture elements), get it?

Are more (mega)pixels better? To some degree, yes. But there is an upper limit dictated by the laws of physics. 10-12 megapixels is usually as many as you need for fine prints up to 13x19". The quality of the lens and the sensor are really more important as they capture the best details and the truest colors.

Now you know how a digital camera works. I hope that this has illuminated the subject and captured your interest. Post a question and I'll answer it promptly.

TOMORROW - A NEW ADVENTURE!!

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