Digital cameras operate much the same as classic cameras. Both camera types need to have a lens with which to focus on the image, a shutter with which to let light into the camera and an aperture with which to adjust the amount of light that comes into the camera.
Traditional and digital photography differ once the light comes into the camera. The traditional camera will capture the image on a film. The digital camera will capture the image on a device that is called an image sensor.
The image sensor is an electronic device that is composed of electrodes (also known as photosites). These electrodes measure the intensity of the light. The CCD (charge coupled device) is the most common image sensor available. Other sensors include the CMOS and the Foveon.
The digital camera gets its megapixel (also known as millions of pixels) rating from the number of photosites the image sensor has. Every photosite is connected to a pixel in the final photo. This means that a camera that has 6 megapixels will have an image sensor that is 3008 pixels in width by 2000 pixels in height.
The light that connects with the image sensor will be changed into electrical signals. These signals are then amplified and moved to an A/D (analog to digital) converter. This A/D converter will change the signals into binary numbers. These binary numbers are then computed by a computer that is inside the body of the camera. After the numbers have been converted the image result will be saved on a memory card.
Photosites will only measure light intensity. They won’t measure color. If you want to create a color image each and every photosite will need to be covered by a filter which is colored. The colors will be green, blue, or red, which are the three primary colors. These primary colors can be blended to create all other colors including the color white.
These colored filters are then placed on a grid. There will be twice as many green colored filters as there will be blue or red. The reason for this is that your eye is doubly as sensitive to light that is green. The filters will be arranged in what is called a “Bayer” pattern. There will be one row of red, one row of green, one row of red (etc). This is followed by a pattern of blue, green, blue, green, etc.
Remember that every photosite can only be used with one colored filter. This means that you need to use computer processing to create an image that has a full color range. Every pixel will be analyzed and a composite color will be produced after they have all been calculated. If a red pixel is in the middle of green and blue pixels, the red pixel will actually be white. This is because white is what you get when you combine red, blue, and green. The name for this process is “demosaicing”.
Once the demosaicing is complete the image will be adjusted to match your camera settings. Most digital cameras will have adjustable settings for contrast, brightness, and color saturation. Once you make the adjustments many cameras will also add an algorithm for sharpening to make the image even clearer.
The last step before you store the image onto the memory card is “compression”. Most digital cameras will use what is called a JPEG format for compression. The compression process reduces the file size by getting rid of extra data. The data can not be recovered, therefore the JPEG process is called a “lossy” format.
Most digital cameras will allow you to save any uncompressed images as TIFF files, also known as raw data. The raw data is what the photosite data was before the demosaicing process. The TIFF files can be transferred to your computer where you can use software to process it with most of the same functions as the camera only with much more control.
Paul Lines is a teacher and has a keen interest in digital photography. His free online photography tips are viewable at http://www.digitalphotographytraining.net. Visit his page to learn new techniques in Digital Photography.
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