subject: Discover How Your Hdr Photography Image Is Created In Your Digital Camera [print this page] These articles explain how a digital camera makes a photograph. First of all it's important to know what "pixels" are and what they do when you are using HDR software or other methods of photo editing.
The light coming through the lens of a digital camera is recorded by a Charged Coupling Device (CCD), or a Complementary Metal Oxide Semiconductor (CMOS). Millions of minute light sensors called pixels put together in a rectangular grid make up these imaging chips. The grid is located in the camera in the place occupied by a film frame in a traditional camera. Pixels are at the foundation of everything that occurs in high dynamic range (HDR) photography and also in normal low dynamic range photography.
Information about the dimensions of the imaging chip for your camera can be found in the camera manual. A two-megapixel camera will normally have an imaging chip 1,200 pixels high and 1,600 pixels wide. Multiplying these numbers gives a figure of 1,920,000, which equates to approximately two megapixels.
Pixel wise the wider or longer your imaging chip is the more pixels your camera will have assuming the size of your pixels stays constant. A high-end professional digital camera like the Nikon D3s has a 4256 pixel by 2832 pixel CMOS sensor and the Canon EOS 1Ds Mark III has a 5616 pixel by 3744 pixel CMOS sensor. Both of these imaging chips are full-frame chips which indicates they are the size of a 35 mm photo frame.
How the pixels are handled from the time you press your camera's shutter in large part determines the quality of the photograph 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 (analog) hitting each pixel have now been converted to a number is the source of the "digital" in digital photography.
Although the term mega pixels may seem puzzling, it's a straightforward idea. Mega means one million. By counting the pixels on the camera imaging chip, and dividing it by one million you find the megapixel number for your camera. On the Nikon D3s there are about 12.1 million pixels, so it is a 12.1 megapixel camera.
People are often surprised to learn that the imaging chips in a digital camera do not discern color. The pixels only record the level of light hitting them, not specific colors.
In order to supply color information, each pixel is given a red, green, or blue filter, so that only that color of light will reach the pixel. This means that each pixel only collects information on one color. These filters are arranged on the imaging chip in a certain pattern, in which approximately half of them are green, as we are more sensitive to green light.
Digital photographs are composed of red, green and blue information (RGB) and each of the pixels in any digital photo file must contain information on all these colors. Other non RGB color models will be dealt with later.
Accordingly, every pixel needs to be able to collect information on the two colors it does not contain. For example, a pixel with a red filter needs to access the green and blue data that the filter has blocked. This is done via algorithms, which largely control the quality of a digital photo.
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 generate the missing color information by sampling the data from surrounding pixels. These algorithms are powerful, complicated 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 extraordinary feature when shooting jpeg photos is that in the time between the click of the shutter and the arrival of the photograph at the memory card, the software algorithms have already provided the two thirds of information needed by each pixel and compressed the file to jpeg. This is indeed a wonder.
