The digital camera
The digital camera is an impressive creation of the engineering art that contains mechanical, electronical and optical elements, microprocessors and software. This technology was derived from the utilitarian American technique, which, during the Cold War in 1960 needed image sensors for the spying planes. At the beginning the Americans worked with analogical photos, which were transmitted by planes on earth through radio waves. Then the images were digitalized and so the digital camera was created, and introduced at the middle of the 90's.
The digital camera photography
Five years ago a digital camera was a
kind of toy. Nobody dreamed to compare it with a serious camera. This attitude
changed. If you spend between 500 and 1500 $, today, you can buy a fantastic
photographic device, one which in reality can offer a photographic quality that
rises at the standards offered by the best reflex cameras. Even the
professional cameramen have begun to use the digital cameras. There's no doubt
that a high quality digital camera is more efficient, interesting and flexible
tool than an ordinary one, at least for a fan cameraman, computer expert.
1. Introduction notions
Light capturing
At a higher level, there are no big differences between a digital camera photo and an analogical one. The exposition in both cases means capturing and stocking bright images. Only this is achieved in different stocking ways:
Film, which can be black and white or colored, positive (slide) or negative;
Image sensor (CCD or CMOS) and RAM memory;
All cameras capture light through a little tube called objective. The light sensitive environment is behind the objective. 525h75f
Film or image sensor
In an ordinary camera, the image is captured and stocked on a film. You can see the result when the film is developed. The developing is a pure chemical process (analogical also).
With a digital camera an image sensor captures the image, which is also an analogical unit. But the digital camera transforms immediately the captured image in digital dates (0 and 1), which are stocked in a Ram memory.
The memory card is the basis of the future evolutions a photo is subdued to (for example, the transfer on a computer or a printer). While an ordinary film contains 24 or 36 expositions, cards can have different dimension types, and an almost unlimited capacity. And if a film can be used only once, a card is used much more frequently. It can be kept several years and can be kept for hundreds of thousands of expositions.
2. The diaphragm
We must measure the light quantity sent by the objective to find the film/sensor zone. The idea is to find the correct quantity of light so that the photo would be neither overexposed nor underexposed.
The traditional camera objective is larger than the digital camera objective.
The objective's diaphragm
The cheapest camera usually has an
immobile diaphragm: the objective can't be regulated. The sophisticated cameras
still have a variable diaphragm that is the objective opening device can modify
its size, just like our eye ball enlarges or diminishes in accordance with the
light conditions.
Altering the diaphragm size, one can regulate the light quantity that passes through the objective. The larger the opening device, the more light will be allowed in the sensible zone (film/sensor).
Clarity
In the classical photography the fact that the medium objective achieves clear photos is always underlined. Before making a photo one focuses the objective at a certain distance.
Clarity expresses how much of your subject zone will be clear. High degree clarity is when the whole zone beginning with the first plan and ending with the wanted subject's background will be clear.
You can manually adjust the clarity, or the camera will do it with the help of the Auto focus function.
3. The releasing speed
The light quantity can be adjusted by the diaphragm's opening device and by altering the exposition time.
The tripping device
The tripping device's opening on a longer period of time allows a larger quantity of light to enter.
An automatic camera will setup alone the time of exposition.
The shortest time of releasing is 1/8000 second. The longest time can be chosen between 1/8, 1/4, 1/2 and 1 second.
The better the camera is, the more flexible the releasing speed is.
4. The objective
The objective is a very important part of the camera. It is a tube that leads the light inside the camera. The objective is formed from glass or plastic lenses and can be immobile or exchangeable.
The objective has a larger focusing distance and different properties.
The objective lens
The objective can be simple (with one lens) or complicated, with more grouped lenses.
The reflex cameras use extremely big and heavy lenses. Both the objective and the lenses of a digital camera are usually small, owing to the very small zone of the image sensor. A digital camera is almost a micro camera compared to a reflex camera.
An objective is characterized by 2 parameters:
The brightness
The length (the focus distance, measured in millimeters)
The brightness is given by the diaphragm's opening an objective can obtain.
The focus distance and the sight
The focus distance (the length) of an objective is measured in millimeters and represents the distance from the optical center of the lenses to the film/sensor.
Most of the modern cameras are equipped with zoom lenses (a kind of variable telescope).
The sight is the changing element.
The digital camera objective
Changing the focus distance of the objective, you can change the angle and so you can obtain a wide-angle or telescopic effect.
A 3X zoom objective can enlarge the subject 3 times from the largest to the smallest angle.
We'll discuss about the digital zoom term. The standard kind of a zoom is the optical one, where the camera lenses enlarge the image. The digital zoom is a pseudo-function, indicated by the producers, but useless in most cases.
Through the digital zoom, the photo is
artificially enlarged. This interpolation
can be realized in any program of image processing.
Bales for auto focusing
Some digital cameras can achieve photos in darkness or in half-darkness, being equipped with an auto focus illuminator.
This is a small source of light that starts automatically in situations in which the focusing function hasn't got enough light.
THE DIGITAL CAMERA STRUCTURE
How does the camera work?
A digital camera has very many things in common with a traditional camera. If we look how light enters in the camera we find:
A lens system including some mechanical elements so the lenses can be adjusted to obtain the focusing and zoom;
A diaphragm and a releasing system;
A measuring instrument for the light and a system for calculating the exposition settings.
All these information are found in both camera types. The lenses gather and focus the light, so that the image is clear on the sensibility camera sensor.
The diaphragm and the releaser adjust the light quantity that depends on the camera sensibility. What is special at a digital camera?
The image sensor replaces the film;
The camera has a LCD screen, with several functions;
A software and data processing are strongly involved in the achieving of the photo;
The photos are digitally stocked and can be immediately evaluated and processed.
Together these 4 circumstances make the comparison between a digital camera and an analogical camera impossible. They are completely different products.
Without film, but with a high resolution
In the case of a traditional camera, the light is gathered in a film that is kept at darkness and later developed. In the case of a digital camera, the "developing" takes place electronically and digitally inside the camera - and in a second or less. The light is gathered in the image sensor, where it's transformed in digital data and stocked in the RAM.
The central unit of a digital camera is the image sensor, an electronic chip sensitive to light
The resolution is one of the parameters used to establish the achieving price of a digital camera. The more mega pixels it has, the more expensive it is.
The term resolution is used for the number of "points" in an image. The more points an image has, the higher resolution it has, and the image is clearer. When we speak about the digital images, the "points" are called pixels.
Software and computerized image
An image sensor isn't a passive stocking medium like a film. The sensor gathers the image data, but this data is immediately sent in the system and processed in the camera computer. The image data gathered in the sensors is primitive; it'll have to pass through a complex process of finishing before becoming a color photo. The camera computer has an impressive number of charges. It takes care of a lot of functions the image data has to pass through to obtain a photo.
The image's colors are artificially recreated with the help of the camera software. That's why the image quality is different from camera to camera.
The LCD screen
Almost all the digital cameras have an LCD screen. It is found behind the main body. This screen has several functions. An LCD screen is excellent, something you get used to very fast and you are very pleased of. It can be used for:
Erasing / editing images.
An LCD screen uses almost all the camera battery energy, but it's the only negative thing you can say about it. Luckily when you want to save the battery, the screen can be turned off and turned back on by pressing a specific button.
Choosing a subject
The most important function of the screen is the viewfinder. When the screen is turned on, it visualizes the subject in front of the objective continuously, and this is the function used to select a subject.
The screen has, normally, a 3-4 centimeters diagonal and enough space for almost 120.000 pixels. Therefore it is a miniaturized edition of the photo and we see it on the screen.
The viewfinder
An analogical camera has only a viewfinder. It is a small hole, in which you can look and that shows you the subject that will be pictured. The viewfinder of the digital camera works exactly the same, but it is neither precise, nor useful. It is used only when the sunrays are too intense to use the LCD display.
The LCD display of performant cameras can be switched in every direction, which makes taking pictures in different positions much easier. A digital camera has a lot of adjustment options; that is why the LCD display is used to navigate throughout the menu, where a number of settings and parameters can be selected.
The typical (most common) settings are:
A lot of cameras have extra, even more technical selection options, which are also controlled by the aid of the menu.
The image sensor
The image sensor is "the film" of the digital camera - and what an excellent film it is! The sensibility to the light can actually be bigger than the sensibility of an ordinary film. That is why the image sensors are so widely used in astronomy, in the structure of the satellites etc.
There are two types of sensors, both used in the digital cameras:
These two types of sensors have different structures:
The CCD sensor is still the most used type of image sensor. It offers a good image quality, but its production is expensive. The CCD also uses much energy, but it is considered an advanced technology and used in most digital cameras.
The CMOS sensor is a completely different type of sensor, sensitive to light, which is not at all technically advanced.
The advantage of the CMOS is that it requires less electronically components than the CCD, and, as a result, it is cheaper to realize.
The CMOS technology will radically simplify the construction of the digital camera and it is only a matter of time until it is adopted.
Even if the sensor of the camera is CMOS or CCD, it has millions of tiny "eyes" used to capture a small quantity of light. The image sensor is somehow like a chess table with small cells.
Every cell is a photodiode (light sensitive electronic device). When a sensor cell is sensitive to light, it reacts by producing an electrical charge - an electrical tension.
The tension charges the cells (like a condenser) in the moment of the exposure and it is relieved into an electron a few moments after the exposion. This small charge is changed into a pixel. This way, every image sensor contributes by a pixel to the final image. So an image sensor is an electronically device which contains millions of sensor cells fixed into a matrix. One point of an image is made by the quantity of light that falls onto a specific photo-sensitive sensor cell. An image is first composed by a gigantic model of tiny electric charges. This "electrical data" must be transformed into bytes (0 and 1) so that the digital image may be formed.
The transition from tension to digital bytes takes place in the Analogical - Digital Converter. The Converter captures the electrical pulses and translates them separately into numbers. Each number shows how much light has fallen onto one of the cells of the image sensor. (0=black, 4095=white).
The more sensitive to the recording of the light differences a camera is, the more details you can obtain in an image. The conversion procedure is called "sampling".
After the conversion, the camera receives the data that will be processed. The image sensor cannot distinguish the different colours of the light; it just records the quantity.
False colours with coloured filter arrays - CFA
How can you obtain a coloured image from one composed in grayscale? It is artificially realized in most of the cameras - by the aid of a colour filter fixed above the image sensor. Every single cell is equipped with a colour filter. In practice, a coloured layer is applied above the photodiode (with a photolithographic process). The filter allows only the light (photons) with a specific wavelength - same colour - to get to the photodiode. The photons that have different wavelengths are absorbed by the filter and do not arrive at the cells. This network of tiny coloured filters is called the CFA (coloured filter array).
The use of every shade of colour is not necessary in a CFA. It is proved that the three basical colours are more than enough. Usually the RGB (red, green, blue) system is used. The complete image is made from these three basical colours.
The interpolation of the coloures and the post-processing
The image sensor captures a mosaic of coloured dots (with one of the three basical colours). But the colours from the real life are combinations of the three. The authentic colours must, then, be reconstructed. This reconstruction, also called composition, takes place in the computer of the camera. It is equipped with software created to compare the data of every cell with the data of the neighbor cells. This way the camera tries to guess the real colour of the pixels. After the interpolation, the colours are remade, but in a pretty primitive version. For a good colour image to be obtained, the data of the image must be digitally processed.
The software analyses every image pixels and balances the colours and the saturation using some exact algorhytms. This type of processing is extremely important for the colours of the final image. They say it represents 50% of the quality of the image. The image sensors are electronic devices that are produced exactly like the ones of a PC processor or RAM memory. But, unlike other computer chips, their dimension has an importance above the consume power.
Price and
dimension
The individual chips are produced in the so-called capsules. They are big, round slices of Si. that are placed in the superior side of every layer and that contain hundreds of chips that are eventually separated one from another. The bigger the individual surface of the sensor chip, the fewer chips are to be extracted from the capsule. So maintaining a low dimension can maintain a low price - the bigger an image sensor, the more expensive it's production.
The tiny sensors are placed in the "common" digital cameras and are an advanced enhancement of the cameras' sensors. Completely different and much bigger sensors are used in the professional cameras. The bigger the sensor is, the bigger is the quality.
The image sensors are passing through major developments. The new models obtain a bigger resolution without increasing the total dimension of the sensor, while the other qualities (dynamics, etc.) are kept and even improved.
The releasing speed
A digital camera must be capable to adjust the exposure time. The photodiodes must have a proper quantity of light. In the traditional camera there is this mechanical obturator that allows the passing of the light only for the necessary amount of time. In digital cameras, the image sensor is exposed constantly to light and it is permanently charged. When we realize an exposure, we choose the image data from one of the snapshots of the camera. At some professional cameras there is also a mechanical unleasher.
The
stockpiling of the image data
Immediately after a digital camera has finished the processing of the image data, the image is saved as a specific image file into a memory card (RAM).
Internal RAM
The image sensor collects a precise dosage of light, which charges the individual sensor cells with electricity. The electric charge is transferred from the sensor cells through an amplifier to the AD Converter, which transforms the electrical tension into bytes. This extremely primitive bitmap that contains unprocessed image pixels is transferred to the internal RAM of the camera.
All digital cameras have a built-in RAM buffer, used for the temporary store of the image data.
The buffer is a part of the internal RAM, which can have from a few megabytes to 128 MB.
An internal RAM has a different meaning then the RAM where we store the images (the RAM card). An internal RAM works exactly the same as the RAM memory of a PC. The internal buffer stores the image data while they are processed by the microprocessors of the digital camera.
When the
processing of the data is finished, the image is transferred to the exiting
device, which is either the LCD or the RAM card.
The RAM card
A digital camera is similar to a computer, and like any computer, it must store the data in a memory bank. While the computer uses the hard disk, most of the cameras are using a RAM card, which is a stocking medium for the image files (and for any kind of data) that can be filled and emptied, having a capacity that can reach 1GB, and can be of various types:
Compact
Flash (CF) - the most used, flexible, cheap, big capacityThe interface with the computer
The most important methods of transferring the data to a PC are:
A. Direct cable connection
B. Docking station
C. A card reader
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