Photography Basics - How Does an Imaging Sensor Work?

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This article is a short excerpt from a book I am writing called, Moving Beyond Point-and-Shoot Photography: The Next Step – Learning to Use a DSLR or Interchangeable Lens Camera, due for release by Rocky Nook in the spring of 2012 in print and most eBook formats.

What is an Imaging Sensor?

In the old days of photography people used various light-sensitive chemical coatings on some sort of base material to make an image. The first real photograph was made in 1826 by a man in France named Joseph Niépce. He set up a box with a lens—called a camera obscura—in an upper-story window of his estate and put a polished pewter plate coated with an petroleum-based substance called "bitumen of Judea" inside the box. He uncapped his lens and let the light from the sunny day outside shine on his coated plate for eight hours. The sun shining though the lens exposed and hardened the sun-exposed parts of the bitumen, while areas that were darker on the image were not hardened. He then took the plate and used a solvent to remove the softer bitumen. What was left was the world’s first geniune photograph made with a camera box and lens. You can read more about this historic event and view the first image at the following web address:

http://www.hrc.utexas.edu/exhibitions/permanent/wfp/

By the 1850s photography had caught on as something enthusiasts of the time could accomplish. It was a lot of work since there was no place to buy pre-made photography supplies. The photographer had to coat his or her own base material with a light-sensitive substance and then process it later into a photograph.

As time went by photography became more and more popular. Companies stepped up and provided pre-made cameras and film to take pictures. Now, any enthusiastic person could be a photographer. For many years the medium of photography was carried by film, either as a negative or a transparency.

In 1888 a man named George Eastman created “The Kodak Camera.” His motto was “You press the button, we do the rest.” Within a year, it became a well-known saying and photography exploded in popularity. The point-and-shoot camera was born! Following is a link to Kodak’s website where you can read about the early development of photography and film-based cameras:

http://www.kodak.com/global/en/corp/historyOfKodak/historyIntro.jhtml

Enthusiasts of the time went beyond Kodak’s method of you press the button and we do the rest. Many had what is called a darkroom, where toxic chemicals were used to “develop” the film for use and the film was placed in an enlarger for printing paper-based prints. Those were the prints of yesteryear. Enthusiasts had to work harder than photographers satisfied with the point-and-shoot method.

Around the year 1999 photography changed in a major way. Companies, such as Nikon, introduced professional digital SLR cameras. Instead of using film, the image was captured with an electronic “chip” inside called an imaging sensor. At first, the images captured did not have the resolution of film and most people didn’t take digital cameras seriously. However, by the year 2002, Nikon and Canon were releasing more consumer oriented and affordable enthusiast DSLR cameras, along with less costly point-and-shoot models. The rest is history.

The camera you now have or desire is based on digital technology. Instead of using film, chemicals in a darkroom, and an enlarger to make prints; the digital camera uses an imaging sensor to capture the image, a memory card to store the images, and an inkjet printer for prints. The whole process is more flexible, faster, yet in some ways, more complex.

How Does an Imaging Sensor Work?

The imaging sensor size in your DSLR or ILC provides potential image quality unobtainable by even the best of the point-and-shoot cameras. Many do not realize why a large-sensored camera can make such high-quality images in comparison. Let me explain.

A CMOS chip imaging sensor found in a Nikon D7000 camera

What is a Megapixel?

All digital cameras have an imaging sensor that uses very tiny light-gathering points called pixels—an abbreviation of “picture-elements” (pix-els). There are millions of these tiny light-gathering pixels on the imaging sensor. Each pixel captures a tiny part of the image of your subject. All the pixels working together capture the full image.

You have heard the word megapixel if you have been doing digital photography for very long. Camera companies use the megapixel rating of their cameras as a major sales point. Most people think that the more megapixels, the better the image; however, that may not be true.

The word megapixel simply means million of pixels. The size of the imaging sensor and the number of megapixels on it determine the maximum resolution (size) of the images you can create with the camera. However, there is a tradeoff in quality when too many pixels are added to a sensor. The problem with a point-and-shoot camera is that the sensor is very small and the millions of pixels are very, very tiny. That can cause some problems, as discussed in the next section.

What about Imaging Sensor Size?

To make a comparison, a point-and-shoot camera has an imaging sensor about the size of your little fingernail. Imagine cramming millions of pixels into a space the size of your little fingernail. Those pixels are so small that they’re not very light sensitive. For a point-and-shoot camera to make a good picture, especially in lower light levels, the power must be turned up on the pixels. That degrades the image by introducing stray spots or graininess in the image, called noise.

You know how static sounds when you turn up a radio to hear a station that is slightly out of range. The static is noisy sound that degrades your radio-listening experience.

Digital image noise is similar to static on a radio, except it is visual. Noise is random specks of grainy-looking dark or light colors that were not in the scene you photographed. Noise is one of the reasons people realize they need better cameras and move into the DSRLor ILC world.

You may remember what noise looks like in images you’ve taken with your old point-and-shoot camera in darker ambient light conditions. The grainy look of the images was not pleasant, was it? A point-and-shoot camera has a much harder time making high quality images because there are too many pixels crammed into too small an imaging sensor size. If you have a point-and shoot camera with 14 megapixels, that means the camera manufacturer packed 14 million pixels onto a tiny little imaging sensor. Noisy images are the result!

On the other hand, a DSLR or ILC has an imaging sensor nearer the size of a big postage stamp. That’s quite a difference! The same number of pixels put into a larger sensor area means the pixels can be much larger and can gather light much more efficiently. The images from your DSLR can be sharper; and have better color, contrast, and dynamic range ( how much light range from dark to light its sensor can capture).

The DSLR/ILC’s photos can be enlarged more efficiently and with higher quality. You’ll be amazed at the difference and so will your friends and family.

If you already have a camera, check its user’s manual to see what size imaging sensor it uses. The larger the sensor, the bigger the pixels can be, and the higher the potential quality of the image it captures. Point-and-shoot cameras have tiny pixels and lower image quality, DSLR/ILC cameras have bigger pixels and better image quality.Pixel size is a strong determining factor in image clarity and lack of noise. As discussed previously, the larger the pixel, the better it can gather light. Sometimes more megapixels is not the best thing for your photography. If a camera manufacturer comes out with a new model with “even more megapixels” and they haven’t increased the size of the imaging sensor—beware!

When there are millions of extra pixels jam-packed into even a larger DSLR/ILC sensor, the pixels must be smaller in order to fit the available space on the sensor. When the pixel size approachs the size of a point-and-shoot camera’s pixels, image degradation can result.

Thankfully, camera manufacturers are usually balanced about this and don’t push the pixel sizes down too far. They know noise will result and people will be unhappy. There was one major camera manufacturer who recently reduced the number of pixels in one of its cameras because people were complaining about noise.

Just don’t be fooled by the hype in advertising. The number of pixels is an important factor in maximum image size, and the size of the pixels is an important factor in maximum image quality. Just be aware of the trade off between the size of the sensor and the number of pixels. More megapixels can sometimes make for a lesser quality image. Interesting, huh?

Keep on capturing time...
Darrell Young



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