A digicam or digital camera is a camera that takes images in digital memory. Most of the cameras produced today are digital, and while dedicated digital cameras are still available, many more cameras are now built into mobile devices , such as smartphones, which can, among many other uses, use their cameras to trigger live video telephony and directly edit and upload images to others. However, high-end, high-definition cameras are also widely used by professionals and others who choose to take higher-quality photos.
A digital camera is a camera that uses, instead of photosensitive film, a sensor (CCD or CMOS) capable of capturing the image and transforming it into an analog electrical signal. The electrical impulses are converted into digital by an A/D converter, in the case of the CCD into a processing chip external to the sensor, in the case of the CMOS, directly from the sensor, having also implemented the A/D converter, in both cases a digital data stream is generated to be stored in various formats on memory media.
The first prototype took place in 1975 and was designed by Steven Sasson, an engineer from Kodak, using a CCD sensor; while the official presentation of a digital machine took place in 1981 with the Sony Mavica, which records images on floppy-disk; while the first fully digital machine took place in 1988 with the Fuji DS-1P, which records images on removable flash cards and uses a CCD sensor.
According to current market rules a distinctive parameter of cameras is the number of pixels. To obtain a good photograph is important a quality optics, a sensor that has a good signal to noise ratio, a good dynamic range and finally depending on the printing needs will choose the resolution of the sensor.
A camera does not “have” its own resolution. This is defined as the amount of pixels produced at the sensor output. In photography instead often counts the depth of resolution, which is given by the number of dots per linear inch, and which is decided during printing. Obviously, cameras with more sophisticated sensors will produce images with more information and therefore they can be printed with a greater number of pixels per inch, with the same print size, than images produced by a less efficient sensor.
The sensor is similar to the one used in portable camcorders. Always and in any case these are photosensitive devices consisting of a matrix of photodiodes capable of transforming a light signal into an electrical one. Using the CCD, the conversion of the light level into digital data necessarily takes place outside the sensor by a dedicated chip, in the CMOS the conversion takes place directly inside the chip/sensor, each photodiode has its own amplifier and A/D converter. In terms of quality, referring to consumer products, one technology does not prevail over the other, only on systems at the highest levels the CCD is even higher quality, responsible are the countless amplifiers and converters implemented in the matrix of the CMOS chip together with the photodiodes, the parameters of which can deviate even a little from each other, which does not happen in the CCD, having the ability to convert the countless levels of the light signal through a dedicated chip, optimized for this function. The disadvantages of the CCD compared to CMOS are higher production costs, slower work, larger footprint and higher power consumption.
In the digital camera, the image is focused on the sensor plane. The signals captured in this way are amplified and converted to digital. At this point, the digital data is in raw form and – as it is – can be stored on a file for further processing in the studio with other computer equipment. Then the image processor inside the camera transforms this data, i.e. it calculates the primary components missing on each pixel (RGB) and makes the image data compatible with normal image display systems (usually in JPEG or TIFF format depending on the needs for which the camera is intended) and finally stores the processed file in a solid state memory (usually from the technological point of view it is EEPROM Flash type, while the formats with which they are marketed are different (CF, XD, SD, MMC, Memory stick, etc.). The cards generally contain a significant number of images, the quantity depends on the size of the single image, the recording mode and the memory size.
The total resolution of the sensor is measured in millions of total pixels. One pixel is the capture unit of the File: it represents the smallest portion of the image that the camera is able to capture on an ideal matrix built on the CCD sensor.
The proportions of the images that are obtained with the current sensors (or through processing of the image processor inside the camera), are indicated in the following figure:
Multiplying the value in pixels of the horizontal resolution by that of the vertical resolution, we obtain the total number of pixels that the camera is able to distinguish in an image.