Whether pro or amateur, if you've made the switch to a digital camera you're probably surprised and perhaps a bit baffled about all the technological choices before you. Should you shoot jpeg, tiff or RAW? How do I download and edit all those photos I'm taking? How do I manipulate my photos to get a great print? How do I get my prints to look the same as they do on my monitor? This series of articles will present the information you need to answer your questions and gain confidence with digital photography.
Before we start talking about an actual "workflow" it's best that we have a common understanding about how a digital camera creates a photograph. We need to know exactly what "pixels" are and how they affect your digital photographs.
Pixels
Digital cameras use either a Charged Coupled Device (CCD) or Complementary Metal Oxide Semiconductor (CMOS) to record the light coming through your camera's lens. Theses chips (from here on, "imaging chip") are constructed of millions of tiny little light sensors called pixels, which are arranged in a rectangular grid. This grid occupies the position in your camera where the film frame would be in a traditional camera. Pixels then, are the basis of all that follows in digital photography.
Your camera's manual will tell you the dimensions of its imaging chip. The imaging chip of a two-megapixel camera will usually have a height of 1200 pixels and a width of 1600 pixels. If you multiply these numbers you get 1,920,000 pixels or roughly two megapixels. Pixel wise the wider or longer your imaging chip is the more pixels your camera will have.
How the pixels are handled from the time you press your camera's shutter in large part determines the quality of the photography you'll see on your computer monitor or printed on paper. When the camera's shutter button is pressed the camera's shutter opens and the imaging chip is provided electricity so the pixels can begin recording the amount of light hitting them. Each pixel acts much like a little solar panel in that it builds a charge as the light continues to shine on it. When the electricity to the imaging chip is stopped and the shutter is closed your camera records the amount of the charge that has built up on the pixel as a twelve-bit binary number (twelve digits of 0 or 1) and saves the numbers from all the pixels to create your photo "file". The fact that the little bits of light hitting each pixel have now been converted to a number is the source of the "digital" in digital photography.
Megapixels
The term megapixel baffles many digital photographers but it is quite a simple concept. If you count up all the pixels on your camera's imaging chip and divide by one million (mega) you arrive at the megapixel number for your camera. There is a difference between the actual number of pixels on your camera's chip and its "effective megapixels". This will be explained later but the difference does not measurably affect your final photograph.
A misconception abounds about megapixels that says the higher the megapixel count of your camera the better its photographs will be. This is not necessarily true! As long as you have enough pixels for the size of print you are making your photos will look great. In the example of the two-megapixel camera if you are printing your photos on a home printer at 200 dots per inch you will have enough pixels for a nice 6" by 8" photo. That dimension was calculated by dividing 1200 and 1600 by 200. Simple as that. If you want to print your photos at 360 dots per inch as do many professionals, you will only be able to squeeze out approximately a 3 1/3" by 4 1/2" print. You can see that the reason you may want more pixels is to create larger prints. But, if you only print in the 8' by 10" size or smaller you may find that a two or three-megapixel camera works just fine for you.
How your photo is created
A little known fact is that the imaging chips in digital cameras do not recognize color. That's right. Each pixel on your imaging chip is only recording the level of light that hits the pixel not which colors are hitting it. To introduce color information to the imaging chip each pixel is covered with a green, red or blue filter that only allows that color of light to hit the pixel. Therefore the digital number generated by each pixel contains the information for only one color. The filters are placed on the chip in a particular pattern and roughly half the filters are green to accommodate the fact that humans are more sensitive to green light.
We know that digital photos are made up of red, green and blue information (RGB) and each pixel in a digital photo file needs to contain information for all three colors. Therefore each pixel needs a way to obtain the information for the two colors it has not captured. In other words, a pixel covered with a green filter needs to find the blue and red information that would have hit the pixel in the absence of the filter. This leads to one of the major components that determine the quality of a digital photograph, algorithms.
In order to create the missing two channels of information needed by each pixel a digital camera contains a software program containing mathematical algorithms that create the missing color information by sampling the data from pixels surrounding it. These algorithms are complicated and powerful mathematical instructions and they are different for each camera manufacturer. The quality of these algorithms can greatly affect the color fidelity of your photographs. The amazing aspect of this process is that between the time you click your camera's shutter button and the time it writes the photograph to your memory card the software algorithm's have created the two thirds of the information required for each pixel. This is truly a marvel.
In our next article we'll look at the next step in the workflow process, saving your pixels to your Lexar memory card. Your camera provides you many options for file formats to save your photograph. Choosing the right file format can make the difference between a barely acceptable photograph and a great photograph. See you next time!
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