Wide dynamic actually refers to the illuminance ratio of the brightest to the darkest part of the image that the camera can see clearly at the same time. In a broad sense, "dynamic range" refers to the span of a changing thing, that is, the region between the lowest pole and the top pole of the change value.
The description of this region is generally the difference between the highest point and the lowest point. The "dynamic range" of the camera refers to the adaptability of the camera to the illumination reflection of the scene, and specifically refers to the variation range of brightness (contrast) and color temperature (contrast). That is to say, the range of "darkest" and "brightest" adjustment of the camera to the image is the ratio of the brightest tone to the darkest tone in the still image or video frame.
As a ratio of the two tones, the dynamic range can be expressed in decibels, bits, files, or simply as ratios or multiples. Because it covers almost all the dynamic ranges that the human eye can discern, the dynamic range beyond these gears is of little practical significance. The reason why the human eye can distinguish such a wide range of dynamics is that the pupils, iris, retina and related muscles interact, adjust dynamically, and at the same time, The brain combines all the "exposure elements" into a coherent image that accurately reflects the very bright or dim tones of the scene.
For standard CCD and CMOS image sensors, the exposure time (photon collection) time of all photosensitive units is the same as that of human eyes. The photosensitive unit collects more photons for the bright part of the scene and less photons for the dark part. However, the number of photons that can be collected by the photosensitive unit is limited by the trap capacity (wellcapacity), so it is possible to overflow or saturate the photosensitive unit that captures the lighter tone of the object. To prevent this, exposure times can be reduced. But if so, the light-sensitive unit that captures the darker tone of the object may not be able to collect enough photons. Therefore, for a typical single exposure image sensor, the upper bound of the dynamic range is limited by the well capacity of the photosensitive unit, and the lower limit is limited by the SNR of the photosensitive unit. Therefore, the dynamic range of CCD camera device is the ratio of the output saturation voltage to the noise peak-to-peak voltage in the dark field, that is, in the dynamic range = Usat/UNp-p (1) (1), the Usat is the output saturation voltage. UNP-P is the peak-peak of noise.
Obviously, the dynamic range can also be defined and calculated in this way, that is, the ratio of the charge quantity determined by the maximum charge stored in the CCD potential well to the noise; Its value is also the ratio of the peak voltage of the output signal to the root mean square noise voltage (usually expressed in dB), that is, the dynamic range = USp-p/UNp-p (2) (2) USp-p is the peak voltage of the output signal.
Therefore, the wide dynamic is the ratio of the brightest brightness signal and the darkest bright signal value to the brightest brightness signal value in the image, which can be seen very clearly at the same time in the particularly bright part and the particularly dark part of the scene, and the wide dynamic range is the ratio of the brightest luminance signal value to the darkest light signal value of the image. There are two main methods to determine the dynamic range of the camera imager: one is to use the relevant information of the basic circuit in the sensor and the image processor to calculate the above formula; The other is to use gray-scale test cards and experimental instruments to collect and observe images and measure image levels.
