(This article is an original article of Bisheng.com and it is forbidden to reprint, and reprinting will be investigated!)
Foreword
Friends who do dry printing, especially those who do pre-press processing, must know the standard drawing. The more common is the ISO standard drawings, so what role do these standard drawings play in the printing process? Why use these pictures as the standard instead of using my dog's photos as standard pictures? I think you are not necessarily able to answer such questions.
In the entire process of printing, due to the actual production needs, many of our images need to be transferred or copied between many different devices, such as printers, computers, faxes, printing machines, etc., due to different equipment, then There will also be certain differences in the replicas we obtain using different devices. Faced with such differences, we need a way to evaluate, so we use standard images. In summary, the standard chart has the following functions:
1. Provide objective evaluation methods in image processing time, system performance, image quality, etc .;
2. Evaluate the image encoding, data compression ratio, or data transmission efficiency;
3. Characterized descriptions can be made for the printed products that are directly output through the traditional printing process or digital.
Standard color images can be roughly in the form of atmospheric natural images and unnatural images. Natural influences include high-resolution images such as skin tones, highlights, dark tones, grayscale colors, difficult-to-copy tree colors, memory colors, complex set images, and so on. Unnatural images include resolution test charts, color scales, arabesques drawn with primary and secondary colors, and CMYK four-color printed images.
All standard color images have two digital numbers. In the first encoding method, the resolution of the image is 16 pixels in millimeters (equivalent to 410 pixels in one inch). The encoding value uses 28 to represent 0% of the printed value (black) and 228 represents 100% of the printed value (white). In the second encoding method, the resolution of the image is 12 pixels per millimeter. The encoding value is 0 for 0% printing value (black), and 255 for 100% printing value (white).
After the above coding procedure, the resulting digital file can be put into the CD-ROM, the file format is TIFF / IT (ISO12639)
Characteristics and parameters of standard color image
For the use of standard color images, there are the following characteristics:
(1) The size of the file can be confirmed
The smallest component unit of digital influence is bit (BIT). Borrowing the set of bits, we can get whether an image is completely converted or restored before and after image processing.
(2) Color sequence
For any color point in the image, whether it is to be printed out or stored in a file, it can be controlled.
(3) Color value
That is, each pixel in the image is assigned a specific position and color value, which is expressed by quantization. The usual setting is eight bits per unit pixel, which is 256 colors. For the quantified value, the range can be defined.
(4) Outlet coverage
The ratio of the area covered by the dots in the image, ranging from 0% to 100%. It must be known that the brightest part of the image has the smallest dot coverage, close to or equal to 0%; the darkest part of the image, has the largest dot coverage, close to or equal to 100%.
(5) Color changes of the whole image
The relationship between the change of the color value of the selected area in the image and the color value of the rest of the image. That is to say, the digital image can be modified separately for the color of the specific area in the influence.
(6) Gray balance
In color reproduction, if the ink volume of the three primary colors reaches a balance, neutral gray can be achieved. Neutral gray produces a color cast, which is easy to detect because the human eye feels particularly sensitive to gray. After the image is processed, if the neutral color and the neutral color value of the copy are the same, then the balance of color reproduction can be regarded as correct.
(7) Color scanning
Color scanners can read photos into digital files through reflection or transmission of light on the photos. These digital files are related to the color space of the overall image.
(8) Reading direction
When reading the content of standard color images, it is a right reading method.
(9) Pixel
A pixel is composed of two words, Picture and Element, and is a unit used to calculate digital images. Like photographs, digital images also have continuous shades; if you magnify the image several times, you will find that these continuous tones are actually composed of many small square points with similar colors, which constitute the image The smallest unit: pixels.
Image resolution is expressed in pixels per inch. When the image is printed or output, the number and resolution of the image will determine the height and width that appear on the printed file. Therefore, for images of the same size, the higher the resolution, the smaller the printed image.
(10) The order of the CMYK four-color values ​​in pixels
The order of the combination of CMYK four-color inks for each pixel in the image is the same as the next adjacent pixel.
(11) Threshold
The threshold of image grayscale segmentation is to process the image separately according to its grayscale. General grayscale segmentation divides the image into two grayscale values.
Any image that needs to do text recognition or stripe recognition can use this method to first simplify a complex image, so how to choose the correct threshold is also an important task.
Description and definition of standard color images
Image information is divided into two types of digital information encoding analysis methods:
The first one is also the main coding method. Its information value range is from 28 to 228, which corresponds to the coverage of the dots from 0% to 100%. The sampling of information is in the 128mm × 160mm image, with 16pixels / mm as the sampling frequency (406pixels / in).
The second is also a secondary encoding method. Its information value range is from 0 to 255, which corresponds to a network coverage of 0% to 100%. The information is sampled in a 128mm × 160mm image with a frequency of 12pixels / mm (305 pixels / in)
After the above two standard color image encoding methods, the digital images generated by the computer each have natural images and unnatural images.
ISO 12640 uses the first image encoding method to generate eight natural images, the code name of which is N1-N8; and the second image encoding method generates natural images, add "letter A" to the N1-N8 code , Namely N1A-N8A.
Natural images include the following characteristics:
(1) Image size
The first encoding method: 2560 pixels × 2048 pixels
The second encoding method: 1920 pixels × 1536 pixels
(2) Pixel color composition
In the image, the arrangement order of the CMYK four-color ink of each pixel is the same as the next adjacent pixel.
(3) Color sequence
Cyan, magenta, yellow, black
(4) Color value
The first coding method: 8-bit binary signal, linear with dot coverage percentage. When the digital signal is 28, the dot coverage rate is 0%. When the digital signal is 228, the percentage of network coverage is 100%.
(5) Image reading direction
When the image signal is read, the reading direction starts from the upper left corner of the image and ends at the lower right corner.
Unnatural images include the following characteristics
In unnatural images, resolution test charts are used to evaluate the resolution capability, netting phenomenon, and various color effects that can be achieved by the image output device. The color scale is used to compare colors and correct errors.
Standard color images are stored in CD-ROM format
CD-ROM data format
The data stored in the CD-ROM contains 36 image file formats. The file name is taken based on the image name. Table 2 gives the file name, size, length and width, and related image names.
The TIFF (Tagged Image File Format) file format is jointly developed and developed by Microsoft and some other companies. It can be said that it is the standard of the digital image format in the industry. It has flexibility, scalability, reliability, and supplementability. The more and more video-related manufacturers are adopting the TIFF file format, their related tool forms are also increasing. However, the TIFF file format is not without its shortcomings. Due to its compatible and coexisting characteristics, its own complexity is very high, and it is more troublesome than other file formats in management or equation writing.
Conclusion
Before printing, the personnel need to evaluate the quality of the digital image, and can compare the original picture as the basis for measurement to change the pixel distribution, which can often improve the quality of the scanned image or even exceed the quality of the original. The quality of digital images is the result of consideration of many factors. Image factors include: scanning image quality, scanning resolution, scanning hardware, operator skills, monitor resolution, gray balance, dot area ratio, resolution , Tone, natural color expression ability, etc. Therefore, suitable image quality should take into account factors such as user needs, system requirements, network infrastructure, and price.
Table: 36 formats of standard color image access on CD-ROM
Table-CD-ROM data contents
Steel Kitchen Santoku Knife,Kitchen Santoku Knife,Professional Santoku Knife,Metal Santoku Knife
GUANGDONG INWIN INDUSTRIAL GROUP CO. ,LTD. , https://www.inwin1979.com