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How does a digital camera works – the image sensor

If you took next to a modern movie camera and a digital camera, you will find that their interiors are very similar in efficiency, in most cases. In fact, until the time of the actual recording of a picture film and digital cameras work very similarly. Yes, it applies to many of our discussions about the functions of aperture and shutter speed the camera. The big difference between film and digital cameras is the presence of the image sensor instead of film. Film draws light and chemical sensors detect the light image electronically.

Digital cameras use an image sensor instead of film to take a picture, eliminating the need for a film transport mechanism. This makes it much easier for manufacturers of digital cameras are very small building, and enable innovative exterior design, which would not be possible with a film camera.

With the exception that an image sensor replaces film, the interior of a digital camera is very similar to the interior of a modern film camera. The light is still traveling through the lens and TTL (through the lens) meter calculates the correct exposure.

When the shutter is activated by light, thereby making the movie or in the case of digital camera, the image sensor to capture the image. At this point, the movie camera to take his job, chemical evolution, when the processed film. The digital camera has more work to do.

The Imaging Sensor (continued)

Film responds to light at a chemical level and requires further processing with photochemistry, to develop the image so that it can be seen. An electronic image sensor responds to light, requiring further processing, so that the data can be collected, how to see a digital photo.

An image sensor is a silicon chip, the millions of tiny electrodes photo sites contain known. The photo pages are arranged in a grid, and there is one photosite for every pixel of the image with the camera. The total number of photo sites is the determining factor for the resolution of the image sensor. The resolution is determined by a number and the time megapixels, to say the only other way in which many millions of pixels of the sensor specified. A five-megapixel camera, it has about five million photo sites or pixels on the image sensor.

Most image sensors can be divided into two main categories: CCD (Charged Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor). The two sensors are slightly different in terms of how to read information. CCD sensors reads, the camera will cost the individual photo pages line by line, like a book, while expenses of photo sites on the CMOS sensors are read simultaneously.

As the light is converted into an electrical response

The two squares represent two individual photo sites (pixels) on the surface of the image sensor. More light falls on the tip, resulting in more electrons (shown in blue) to collect them. When interpreting the analog-digital converter of the camera, leading to a higher value for the clear digital sound.

If the exposure is complete, the computer measures the camera in the amount of electrical charge, electrons, or accumulated at each pixel position. This electrical charge directly correlated to how much light hit that particular pixel. This first set of information about exposure is the raw data by the image sensor. We will talk more about the importance of this raw data later.

The A / D converter

With the first song, the stress response of the photo pages to the camera, the data are processed by an analog-digital converter (A / D converter), which translates the voltage number into a digital value. Most digital cameras for consumer use an 8-bit A / D converter. This means that the electric charge of each pixel in a number between 0 (black) to 255 (white) is transformed, creating a single image with 256 color gradations.

Many prosumers (consumers with professional equipment) and professional 35mm models, but the A / D converter 14-bit images, which translates to 16,384 tones process. Images that can use more than eight bits are only accessible if you have the RAW file option.

The Creation of Color Image
If sophisticated and technologically advanced as the image sensors of digital cameras can be, they have no images in color. The truth of the matter is that today’s sensors are color blind, and they can only see the world in shades of gray. The pixel values ​​represent brightness they produce alone. With the exception of the Foveon X3 image sensor (which, as I write this, is currently only available on the Sigma SD10 camera), although the image sensors are currently used to capture gray scale images.

To determine the color values ​​in an image, each pixel on the sensor also has a color filter. These filters are arranged in a certain pattern, with most cameras with filters alternating green and red and blue and green, in every other row of pixels on the sensor. This arrangement is known as a Bayer pattern. The Bayer pattern has twice as many green filters as red or blue because the human eye is particularly sensitive to light-wave frequencies in the vicinity of green that falls in the middle of the visible spectrum.

So the image by the A / D converter is processed in a grayscale file, where each pixel has a value of only red, green or blue. Looking at a color picture, however, each pixel values ​​for all three colors. To assemble the puzzle and determine the missing color values ​​is a process of color interpolation. Interpolation is the addition of new data based on existing information.

In essence, the computer sees the camera, every pixel and the surrounding color values ​​and makes a very good educated guess as to what should be the lack of color numbers. Obviously this is a call bet is a simplification, and there is no justice for the extremely complex mathematical algorithms, which play a role in the final, full-color stills.

The color filter pattern on a pixel image sensor captures alternately red, green and blue. Twice as many green pixels as red or blue record. A complex system of color interpolation, then takes the resulting color image.

Wow, so all that sounds very technical, but the premise is pretty simple. Remember, in terms of something familiar. For example, if you were looking in a magazine photo with a magnifying glass, you see the pattern of dots that are actually creating the image. Unlike a true continuous model as a traditional black and white or silver-gelatin photos are raster images of tiny dots, which are generally small enough to see our eyes, a half-tone fool together. Cheap newspaper publications are often coarse dot pattern, which are visible without a magnifying glass. Digital images of the same function, but the grid points is called the image of small squares, even pixels that are the same size, but can vary in color and tone.

Additional in-camera processing
Included in the image from the sensor was processed by the A / D converter and interpolated into a full-color image, the camera can apply additional processing. Whether this extra processing is done (and what it means) depends on the individual camera and some custom settings. Normally the camera will use what we like to call “secret recipe”. This is is basically a list of guidelines for brightness, contrast, color saturation and sharpness adjustments for each camera.

Some of the settings can not be changed by the user or totally disabled.

Most cameras can adjust the sharpness, contrast, brightness and saturation. For more flexibility, it is often best, such adjustments later in image editing software and not when the picture. Photoshop is basically a more productive software package in relation to the internal software used in digital cameras. (Note:. If the settings are not changed in the camera, these so-called firmware)

After the last round of in-camera processing, you have the file and the metadata (information about the photo) is written to the memory card in the chosen file format (usually JPEG). At this point, the camera is processed on a different picture. This all happens very quickly, of course, so you do not really notice the incredible work going on in your camera. But it’s pretty amazing when you really stop and think about all the steps, if you focus on a subject and press the shutter release occur.

Another feature of a CMOS, which distinguishes it from a CCD is the only major power consumption when the transistors between on and off. Therefore, CMOS is extremely energy efficient and can dissipate heat better.
CMOS technology is used in many commercial applications and as a result, produce it economically. Until recently, CCDs produced a superior image quality and a higher dynamic range. CMOS sensors are now improved and produce similar image quality of CCDs. In fact, has become the standard CMOS in the coming years due to the economics of production and efficient use of energy.

Before you actually take a picture, the camera is the sensor data prepared by the elevation of the surface of the sensor obtained with electrons. When the shutter opens, so that light hit the lens on the sensor, the electrons gather on the pixels in an appropriate response to the amount of light that strikes each pixel. More light falls on a given pixel means to collect a larger number of electrons.