Advantages and uses of traditional photographic images and digital photographic images
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When people watch a modern traditional photographic image and a digital image, they can be discerned with a little attention to the observation and analysis. The image is vivid, the level is full and soft, and the color is beautiful. The other one looks like a colorful, eye-catching, contrasting, clear-cut image of a digital photo print. Why are their respective advantages so obvious? This is explained from their respective imaging principles and production processes.
1 Imaging principle and manufacturing process of modern traditional photographic photoimageable materials
Modern conventional photographic light-sensitive materials include general art photographic film, photographic paper, telecine film, aerial photographic film, medical X-ray film, film used in printing plate making, film for some microfilms, astronomical dry film sheets, and the like.
Generally, modern traditional photographic photosensitive materials cannot directly obtain images after photographic exposure, and usually undergo chemical processing such as development, fixing, water washing, drying, etc. to obtain visible and long-lasting images, so that a complicated image forming process is divided into three basic stages. , the photographic exposure stage (forming the latent image), and the development stage (forming a visible image).
1.1 Photosensitive material preparation stage
The first is the preparation of photographic emulsions. The requirements for the use of each type of photographic film are different. The raw materials used in the preparation of photographic emulsions are different from those of the manufacturing process. According to the formulation and process technology of various kinds of tablets, the prepared potassium bromide (potassium halide, potassium iodide) and silver nitrate aqueous solution are injected into the aqueous solution of a certain temperature of photographic gelatin which is being stirred in the dark room by double injection method. The potassium bromide is chemically reacted with silver nitrate to form a precipitate of silver bromide, which is uniformly deposited on a gelatin carrier to form a photographic emulsion.
The emulsion is subjected to a very complicated manufacturing process under a dark light, such as washing potassium nitrate with ice water, adding a chemical agent such as a sensitizer, an anti-fogging agent, a leveling agent, a defoaming agent, a hardener, and the like. Become a formal photographic emulsion that can be applied.
Coating and finishing section: The above photographic emulsion is tempered to 5~8 ° C under a dark room, injected into a coating machine coating tank, and then coated on a film base or photographic paper carrier, dried at a low temperature, and cut Cut, punch, and pass the test into a product after inspection, put it into the warehouse, and put it on the market.
1.2 Traditional film exposure stage
The photosensitive center on the silver bromide crystal in the photosensitive material film undergoes a chemical change due to absorption of light energy during exposure, and a part of the silver bromide is decomposed to generate a latent image of silver and bromine. At the time of exposure, the density of the latent image formed by the portion of the film illuminated by the strong light is large, and the latent image is the center piece. They will affect the next development speed and the density of the shadowed metallic silver particles and the quality of the image.
1.3 Development stage of traditional photographic photosensitive materials
Development is the use of a developer to chemically change the silver bromide crystal particles in the exposed silver halide emulsion to form metallic silver particles. Therefore, in order to study the development progress, it is also possible to start from the development of individual silver halide crystals, and the development of silver halide grains always starts from a certain point or some point above. The reason why the development is started from a certain point or some point above is due to the effect of the latent image. The latent image can cause the silver halide around it to be quickly reduced to metallic silver. When these silver halides are reduced, they in turn promote the reduction of the surrounding silver halide until the entire silver halide is reduced. The latent image plays a catalytic role in developing or accelerating the reduction of silver halide by the toner during development.
The structure of the metallic silver particles obtained by development is not a solid mass, but a filament-like structure having a size roughly equivalent to that of the original particles.
From the above, it is seen that the particles of silver ions and metallic silver particles play an absolutely decisive role in the preparation of the emulsion or in the exposure and development of the film or photographic paper. Because their slender particles are close to the size of the nanometer, the fine particles are scattered and aggregated into a beautiful image, the color is soft and delicate, and the layers are distinct and full, which makes people feel the beautiful art enjoyment when watching.
Modern traditional photographic light-sensitive material images are extremely versatile. Such as art photography, tourist scenery, wedding photography, celebrity giants standard image, painting of famous painters, as well as images in activities such as cultural and educational sports, industrial and agricultural production, scientific research, printing and electronic circuit intermediate plates.
2 Principle and use of digital photography
The front of the digital camera body is equipped with optical lenses, framing frames, quick-moving and other components, and the operation method is similar to that of a conventional camera. The biggest difference is that the photoelectric camera is equipped with a photoelectric charge-coupled conversion device CCD. When shooting images, the optical lens is used to focus the scene onto the CCD. Under the illumination of light, the CCD pixel generates a current due to the change of the charge distribution. The stronger the light, the larger the current. The binary code (image code) whose current is converted to "0" or "1" is stored in the memory, which is equivalent to the exposure process in a conventional camera. In order to generate a color image, the light is passed through a set of red, green, The blue filter falls on the CCD pixel and is combined by the signal to produce a color image. Obviously, the more the number of CCD pixels, the higher the resolution of the image, and the larger the storage space occupied by each image. In fact, the storage space occupied by each image is too large (usually hundreds of images per image). KB to MB), so many digital cameras compress the image information and store it on the internal memory stick.
The next step is to transfer the image on the digital camera to the computer for editing. After the user is satisfied, it will be transferred to the printer for printing. Finally, a beautiful image will be obtained (the digital photo can make a large image).
2.1 CCD Photoelectric Charge Coupled Conversion Device
CCD, the photoelectric charge-coupled conversion device, has been developed on the basis of metal oxide-semiconductor devices and has become a very mature solid-state image sensor. In addition to capture processing and image sensing, CCD can also be used for information processing and information storage, image analysis and processing. The two-dimensional CCD produced by Optics is mainly used for still electrophotography. The Kodak company has developed:
2.1.1 Full Frame CCD Image Sensor
The CCD sensor is composed of many identical basic units (pixels) each having a photosensitive area and a storage area. The photosensitive area generates photoelectrons, and the accumulated charges are transferred to the storage area and then output through the shift memory.
The full frame CCD is an image capture device of a photosensitive unit combined with a memory unit, and its image capture process is divided into two parts, namely integration and readout. In the integration region, electrons generated by photons are accumulated in the image forming unit, and the number of electrons accumulated in each CCD pixel corresponds to the illuminance of the image, and the charge accumulated in each pixel in the readout region is transferred to the output circuit. Such a CCD is simple to manufacture, easy to use, and has a small signal, but cannot be seen when reading. Therefore, a mechanical shutter is required in the camera, and the blue spectral response is also low.
A color filter is added to each pixel of the sensor to form a color imaging sensor. The dye filter array produced by this photographic method is called CFA, because the human eye is most sensitive to the green part, so the CFA feels The number of green cells is twice that of the red and blue units.
When the illuminance is too large, when the charge generated in the pixel exceeds the capacity of the pixel, the excess charge will be stringed into the adjacent pixel, causing the image to be blurred, and the function of the lateral overflow (COD) is to charge the excess charge before the charge is saturated. Leak out.
The CCD used in amateur still photography has COD because the scene cannot be controlled. Cameras used in industrial and scientific fields where photographic conditions are controllable do not have COD. It has high sensitivity and large pixel capacity.
2.1.2 6.4M pixel image sensor
The Kodak professional digital camera DCS200C uses 1029×1526 sequential scanning CCD to capture images, the internal hard disk drive stores images, and the megapixel electronic camera outputs color hard disks, the quality far exceeds the level of still video cameras.
A rotating color filter wheel is added in front of the camera lens to enable the CCD sensor to receive red, green and blue images in sequence, so that only one single color CCD can capture the color image, such a color sequence capture method has high resolution and color reproduction. it is good. However, due to vibration and the like, the camera and the scene are relatively moving. When the red, green, and blue images form an image, the problem of inaccurate color registration may occur, so it is only suitable for shooting still scenes.
The most suitable capture camera for still photographic images is a full-frame CCD. The advantages of the full-frame structure are high sequential scan occupancy, low noise, wide dynamic range, and high pixel density.
The image taken or scanned into the computer can be processed with the corresponding image processing software, and it is very convenient to process the image on the Windows platform. Because the image processing software opened under the platform has many varieties and functions, it can carry out various processing and processing that people can think of. Adobe Photoshop software is currently the best choice for making the produced slides reach the photo quality level, making them colorful, beautiful and effective. Photoshop software is one of the first image software developed in the world, featuring powerful features and easy operation. The software can at least process and trim the image file.
2.2.1 Brightness and Contrast Adjustment: The brightness and contrast of the whole or partial image can be adjusted arbitrarily, thus showing the effects of different image effects and traditional techniques.
2.2.2 Color adjustment: The color level can be adjusted to remove unwanted colors, and the color cast and saturation of the color can be adjusted and corrected intuitively, and the positive and negative images can be easily converted to each other.
2.2.3 Eliminate fog, spots, and red eyes: Image processing software can be used to easily eliminate artifacts on the screen and adjust image sharpness.
2.2.4 Change the image texture: make the image produce various deformations, and get an innovative and unique artistic image with many different formats, such as: displacement - make the pixels of the image in different directions Shift, squeeze (Pinch) - squeeze the image inward or outward, coordinate transformation (Polar coordinates) - change the image coordinates from Cartesian coordinates to polar coordinates or polar coordinates to Cartesian coordinates. The square object becomes a circle, and the text or object is three-dimensionalized to create a bulging effect and the like.
2.2.5 Produce a variety of painting styles: the image can be processed to obtain different styles of painting effects, mainly with a soft focus effect (diffuse) - making the image look like a blur through the frosted glass effect (making the picture rich Poetics; embossing - an embossing effect on an image background that causes a convex or concave object to appear in an image; extrude--transforming an image into a series of three-dimensional cubes or cones, which can be used Change the image or generate a special three-dimensional background, the size of the cube or cone fan, the height of the protrusion can be artificially selected; the hooked effect (findedges) - make the image look like a pencil sketched; the brick effect (tiles )--Processing the image into the effect of building blocks; wind effect--increasing the effect of some small horizontal lines to generate wind, the wind direction, the strength of wind effect can be chosen by anyone; pointillize effect--will be an image Divided into random points, producing an effect like a point painting; mezzotint--generating an engraved gravure image that brings the original image closest; fragmentation--making the image unfocused As a result, the focus is not used for the rapid formation of background above kind can be attached to the catching protrusion like kind.
2.2.6 Others: such as simulating the shooting effect of various materials and simulating the processing effect of traditional darkroom techniques.
3 inkjet process
First, there must be a qualified inkjet printer and computer software using the inkjet printer, including the image drum speed of the inkjet image that the user needs, the transfer speed of the special paper conveyor, the temperature of the heating roller, and the various colors of the inkjet nozzle. The edited software such as ink sequence, speed, usage, and evaporative drying speed after image printing is input into the computer.
Before the inkjet printing, it is necessary to strictly clean the inkjet printer and check whether the preparation work is in place.
Apply the inkjet image software command of the inkjet printer to start the inkjet printer program for inkjet printing. According to the performance of different inkjet printers, Beijing Yunyuan Digital Co., Ltd. has a complete set of inkjet printer software for users to choose.
There are many types of inkjet printers. The inkjet printers produced by various production companies have their own characteristics and patents, and their sizes and sizes vary, but generally include the various components shown in Figure 3.
3.1 Inkjet print head on the inkjet printer
The inkjet printhead on the inkjet printer has different structural designs, as shown in Figure 4, Figure 5 and Figure 6. Different inkjet printers have different inkjet print heads. The nozzle diameter is about 4μm. Generally, according to the pixel point, such as Epson color stylus is 1440×1440dpi, Lexmark 7000 is 1200×1200dpi, and the nozzle of the inkjet printer has more pixels. The inkjet printer has a large nozzle opening density, a small nozzle diameter, a small ink droplet drawn by the inkjet, and a small number of pixels lost in the inkjet image, and the produced image is naturally fuller and more realistic.
The reason why the image printed by the general digital camera has a sense of distortion is that the pixel reflected by the ink droplet splashed on the carrier paper reflects the particle size of the molecular level, and the particle point has a certain distance from the particle point and is lost. A lot of pixels, resulting in a large contrast of the image, the level is clear, not soft and full, the human eye looks uncomfortable, has a sense of distortion, which is why it can not be compared with the beauty of traditional photographic images.
3.2 Printing special paper
If a general paper is used for inkjet printing, a drop of ink is sprayed onto the paper as shown in Fig. 7. The ink points are still oozing around and penetrating into the deep layer of the paper, and the wet image of the ink dries slowly, affecting the printing speed. In order to prevent the ink from penetrating and accelerate the evaporation drying speed of the ink droplets, it is generally applied to the surface of the paper with a coating containing a high polymer cement and titanium dioxide (TiO) or talc (SiO2). The coating thickness is matched to the ink. It helps absorb some of the ink's moisture, which can promote the image to dry quickly, shorten the spray drawing time and reduce the cost.
4 Advantages and uses of digital photographic images
4.1 The advantage of digital photographic images is that the methods used to make them are diverse, the images are real, the colors are bright, the levels are clear, and the contrast is clear.
4.2 Uses: It can be used in almost all places where traditional photographic images can be applied. It is widely used in CT, MR, DSA, ECT, US and other digital medical imaging inspection devices. It is also most suitable for large-format images. Such as various policy promotional images, product advertisements, light box patterns, and so on.
Its only shortcoming is that the images reproduced with it are not as realistic as the images printed with traditional photographic materials, the colors are beautiful, the layers are full, and the contrast is soft.
5 Conclusion
From the advantages and uses of the above-mentioned conventional photographic images and digital photographic images, it can not completely replace the application of traditional photographic images in view of the current quality level of digital photographic images. People will take advantage of their respective strengths and avoid them, and they will coexist for a period of time.