Comparison of Digital Imaging and Photographic Imaging Principles

The birth of the first photo in 1839 caused a sensation in the world. Photographic imaging has become the focus of attention in the academic and industrial circles. Until today, people are still doing tireless research in this field in order to achieve more ideal imaging results. However, with the continuous development of computer technology, digitalization has become a trend of social development. Digital cameras have entered people's lives and become a strong opponent of traditional photosensitive media. Especially in the field of printing, digital cameras are favored by the news media industry for their advantages of timeliness, convenience and flexibility.

What is the difference between the two different imaging technologies and how they should be selected in the printing field is very important for many printers. The following is a comparative analysis of the different advantages of the two technologies.

1 Analysis from the principle of imaging

From the imaging principle, conventional sensitometric imaging uses an imaging lens to image an objective object on a film coated with an emulsion, and photochemically reacts on the surface of the film. The degree of chemical reaction on the surface of the film is determined by the distribution of the light intensity with the image information and the exposure time, so that the exposed film can record the image as a latent image. The exposed film is processed by developing and fixing in a dark room condition to obtain a negative film with a cured subject image. The negative film is further imaged by a projection objective of a photographic magnification machine and further imaged on a photographic paper coated with an emulsion. After developing and fixing the photographic paper, we can obtain photos in the usual sense.

Digital imaging is to obtain the optical signal of the scene through the optical components. The optical signal is converted into an analog electrical signal. After analog-to-digital conversion, the electrical signal is converted into a digital signal, compressed and stored in a memory card to form a digital image. Digital imaging and traditional sensitometric imaging are fundamentally different in imaging media: traditional cameras use silver halide as a light-sensitive recording material, and digital cameras integrate light, electricity, and laser as one, using CCD/CMOS and memory cards as charge-coupled devices. Image conversion and recording elements. The image information in the memory card can be output to a computer for post-processing. Through the printer, CD recorder or Minilab, etc., the images can be output to different media such as paper, optical disks, and photo paper.

From the imaging principle of the two, it can be seen that photographic imaging is continuous modulation analog imaging, and digital imaging is digital imaging after discrete sampling. The discrete sampling accuracy of digital imaging depends on its hardware sampling accuracy. For digital imaging effects to achieve continuous modulation effect of photographic imaging, the sampling accuracy must reach a very high (about 20μm), but from the current accuracy of digital imaging sampling hardware CCD/CMOS, it is difficult to achieve the accuracy of photographic imaging. Therefore, when printing a high-end color album (such as 120 reversal film or loose-leaf sheet), it is best to use the traditional high-end photosensitive imaging method to obtain images. In the general printing field, especially in newspaper printing, digital imaging with a higher pixel (500 to 6 million) can completely replace photographic imaging.

2 Analysis of the advantages of both

First of all, digital imaging has many advantages over photoreceptor imaging:

1 instantaneous display photography effect

Digital imaging can be used to instantly reproduce the effects of a shot taken by a digital camera's liquid crystal display.
2 Allow retake

Even the best photographer can't guarantee that he will get the perfect picture for every shot. Digital photography can immediately delete unsatisfactory images until each image is satisfactory.

3 easy image post-processing

The special effects of traditional photographic negatives or photographs need to be handled by experienced professionals. The specific processing process is rather complicated and cumbersome. The digital image obtained by digital imaging can be directly input into a computer and subjected to special effects processing using computer image processing software. Whether it is a digital camera vendor's processing software or Photoshop can provide powerful image processing capabilities. The special processing methods such as contrast correction, exposure correction, color reconstruction, and multi-image synthesis are unmatched by conventional photographic film or photo processing.

4 convenient shooting, fast transmission

Compared with traditional cameras, digital cameras are smaller and lighter, and the storage capacity of a slightly larger memory card is equivalent to several films, thus eliminating the need to frequently change film. Furthermore, digital cameras record images in the form of digital signals, and eventually save the images in computer image file formats. Therefore, it is possible to use all the most advanced modern communication means for fast transmission, such as direct transmission over the Internet, or through satellite ground stations. For ultra-long-distance image transmission. In the current information age, digital cameras have special significance for improving the transmission speed of news image information and for the timeliness of news.

5 can accurately copy and long-term preservation

Due to the limitation of the optical transfer function, the copying of traditional photographs will inevitably lose some of the information to a certain extent (more or less total loss during the doubling and scanning), thereby reducing the quality of the photographs. Moreover, the preservation of traditional photochemical negatives and photographs requires high environmental conditions. The digital image obtained by digital imaging does not lose any information during the copying process, and digital images saved in the form of computer files can be stored on hard disks and optical disks for a long time.

6 color reproduction is good

The conventional color film and photographic paper are composed of blue, green, and red three-layer emulsions. In the sensitization process, the sensitized green layer and the red sensation layer can also experience different shades of light at different levels, resulting in complementation. Excessive absorption of color affects the saturation of color. Although it can be corrected with various types of filters, it is difficult to completely eliminate them. The digital camera replaces the chemical changes on the silver halide film with changes in the electrical characteristics of the CCD chip, and generates currents of different magnitudes depending on the intensity of the incident light, thereby obtaining images of different tone levels. The CCD does not directly record the color. It records the digital signals of blue, green, and red light on different CCD light-sensing units through a micro color filter array (CFA). The recorded bit depth is 8 bits. In other words, the entire imaging system can produce 256×256×256 colors, and the image color reproduction is better than the silver halide film.

7 High definition

Compared to photos with the same number of pixels, from a sensory point of view, digital photos are clearer than traditional photos, which is mainly due to the sharpness. Digital photos are more sharp and sharp than traditional photos. This is caused by two reasons: On the one hand, the CCD is better than the film for the reproduction of contrast (CCD MTF value can be significantly higher than 1); on the other hand, the edge of the digital image is sharp, especially the large-area CCD professional The digital camera is more sharp and sharp.

Similarly, sensitometric imaging also has many irreplaceable advantages of digital imaging:

1 good detail reproducibility

Silver halide film in photographic imaging can capture continuous hue and color, while CCD components in digital imaging lose some detail in darker or brighter light. This is because the pixels captured by the CCD element are lower than the photosensitive image. The number of pixels. A handful of large format digital cameras can reach tens of millions of images, but the price is amazing.

2 continuous shooting function

Every time a digital camera takes a picture, the data must be cleared, compressed, and stored. This takes a certain amount of time, so there is a 2 to 7 second gap between the two shots, and the traditional camera does not have the problem of shooting delays. can capture the exciting moments, especially in the sports lens capture? (author: Wang Wenjing)

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