What is the dynamic range of a digital camera?

Dynamic Range of digital cameras

Dynamic Range is the first concept of a signal system. The dynamic range of a signal system is defined as the maximum undistorted power and noise level difference. In actual use, the logarithm and ratio are used to represent the dynamic range of a signal system. For a negative scanner, the dynamic range refers to the tone range in which the scanner can record the source, that is, the difference between the latest density (Dmax) and the latest density (Dmin. For film and photosensitive elements, the dynamic range represents the range from "shortest" to "shortest" contained in the image. The larger the dynamic range, the richer the layers that can be represented, and the wider the color space.

The larger the dynamic range of a digital camera, the more details it can record at the same time. Note that the dynamic range and tonal range are different.

When we take a photo in JPEG format, the digital camera's image processor records the image information in a tone curve with strong differences in light and shade. In this process, the processor often saves the dark and bright details of some raw data. In raw format, images can maintain the dynamic range of photosensitive elements and allow users to compress the dynamic range and tone range with an appropriate tone curve, make the photo output to the display or be printed out to obtain the appropriate dynamic range.

The photosensitive elements of a digital camera are composed of millions of pixels which absorb photon during pixel exposure, convert them into digital signals, and then perform imaging. This process is like taking millions of buckets to the outdoors to collect rain. The brighter the photosensitive area, the more photon the collected. After the photosensitive elements are exposed, they are given discontinuous values according to the amount of photon collected by each pixel and converted into digital signals. The pixel values that do not absorb photon and that do not absorb photon to full load are displayed as "0" and "255" respectively, that is, they represent pure black and pure white.

Once these pixels are fully loaded, the photon overflows, causing information (details) loss. Taking red as an example, the highlight overflow changes the values of other pixels near the red pixels to 255, but their actual values do not reach 255. In other words, the details of the image are lost, which may lead to missing information in the highlights. If we reduce the exposure time to prevent high light overflow, many pixels used to describe the dim environment do not have enough time to receive the amount of photon, and the resulting pixel value is 0, this will lead to missing information in the dim part.

Through the above instructions, we can now understand why digital SLR with large size photosensitive elements has a larger dynamic range. The reason is very simple: the size of the photosensitive element of a digital SLR is generally 4 ~ 10 times, allowing more pixels to be carried without narrowing the distance between image points, resulting in noise. More pixels will not be quickly "filled", so the pixels that represent the dim environment have more time to absorb the photon before the pixels that represent the bright environment are "full, as a result, the image details will be richer.

The dynamic range Representation Methods of digital cameras, such as DSLR and DC, do not seem to have uniform restrictions at present. Each manufacturer only mentions "large dynamic range" in their promotion content, no specific indicators are provided. So sometimes we use a ratio to describe the dynamic range of DSLR, or convert it into the number of optical circles, rather than the concept of density value.

Because Digital Image devices can also be seen as a signal system, the dynamic range can be divided into two parts: the Optical dynamic range and the output dynamic range.

Optical dynamic range (dr_optical) = saturated exposure/noise exposure (dark current)

Output dynamic range (dr_electrical) = saturated output amplitude/Random Noise

The former is mainly determined by CCD/CMOS Sensors, and the latter is mainly determined by A/D and DSP. The saturated exposure is equivalent to the shoulder range of traditional films, and the noise exposure is equivalent to the toe range of traditional films.

For a digital camera, the output dynamic range formula is not applicable because it is still output in numbers. The dynamic range we mentioned mainly refers to the dynamic range of the input part, which is equivalent to the width of the film.

According to some tests we have seen, the optical dynamic range of DSLR is basically similar to that of the negative slice, which exceeds the reverse slice.

In general, it is the difference between the maximum value and the minimum value.

 

Dynamic Range and Imaging Technology

High Dynamic Range Imaging in calculator graphics, film, photography, and video technology) it is a group of technologies used to achieve a larger exposure dynamic range (that is, a larger gap between light and shade) than ordinary digital image technology. The purpose of high dynamic range imaging is to correctly express the brightness of a range from direct sunlight to the shortest shadow in the real world.

High-dynamic range imaging was initially used only for images generated purely by calculators. Later, some methods were developed to generate highly dynamic range images from different exposure ranges. As digital cameras become increasingly popular and desktop software becomes easy to use, many amateur photographers use high-dynamic range imaging methods to generate photos of High-Dynamic Range scenes. However, do not use this as its only purpose. In fact, there are many other applications in the high dynamic range.

When used for display, high-Dynamic Range images often need to be hashed and used together with several other full screen effects (full screen effect.