The best effect of displaying the original: analysis of resolution of prepress equipment (I)

A scanner

Most scanners currently on the market have software and hardware extensions to the resolution. Some scanner ads only write 9600×9600 DPI, which is the maximum resolution obtained by software interpolation, not the true optical resolution of the scanner. So for the scanner, its resolution has optical resolution (or optical resolution) and maximum resolution.

We say that the resolution of a scanner is as high as 4800 DPI (this 4800 DPI is the sum of optical resolution and software differential processing), which means that when the image is input by the scanner, 4800×4800 pixels can be acquired on the 1 inch2 scan plane. Scanned area of ​​1inch2 square, scanned with a resolution of 4800DPI produces an image size of 4800×4800 pixels. When scanning an image, the higher the scanning resolution is set, the finer the generated image, and the larger the generated image file.

Second, the printer

We say that the resolution of a certain printer is 360 DPI, which means that when using the printer to output images, 360 color dots representing the output of images can be printed on each inch of printing paper. The larger the number representing the printer resolution, the smaller the color point that characterizes the image output effect, and the finer the output image.

For images with a fixed file size, the larger the printer resolution, the smaller the printed image size. The size of the printer's color point is only related to the printer's hardware process, regardless of the resolution of the image being output.

Third, the monitor

We say that the resolution of a certain brand of display is 80 DPI, which means that within the effective display range of the display, the display's imaging device can produce 80 spots on each inch of the screen. For example, for a 14 inch display (the screen diagonal length is 14 inches) with a pitch of O.28mm, then: Display Resolution = 25.35995mm/inch ÷ 0.28mm/Dot = 90DPI (1 inch = 25.3995mm).

The DPI value that represents the resolution of the display is generally not displayed when the display is shipped from the factory. Only the dot pitch is given. We can calculate the resolution of the display according to the above formula. Based on our calculated DPI value, we can then calculate the maximum display mode that the monitor can support. Assume that the diagonal length of the effective display range of the 14 inch display screen is 11.5 inch. Since the horizontal and vertical display ratio of the display is 4:3, the horizontal width of the effective display range may be set to 4 inches and the vertical height to 3 x inches. The Pythagorean theorem in mathematics can be obtained as x=11.5÷5=2.3inch. Therefore, the effective display range width is 2.3 x 4 = 9.2 inch and the vertical height is 2.3 x 3 = 6.8 inch. The maximum display mode is approximately: 800 (9.2 x 90) x 600 (6.8 x 90). In this case, one pixel is represented by one dot.

The above mainly describes the device resolution of scanners, printers and displays. Strictly speaking, the resolution of the device and the resolution of the image processed by the device are two related and different concepts. The device resolution is determined by the production process of the hardware device. Although the resolution of some devices can be adjusted by software, they all have a very limited maximum resolution, and the user cannot make any breakthrough on it.

When describing and understanding device resolution. We must rely on the resolution of the image it handles. The resolution of an image is a measure of the fineness of the image itself. For scanners and printers, the resolution of the image is measured by the number of pixels per inch, or PPI (Pixels Per Inch). For computer video processing, the resolution is represented by the number of pixels that can be displayed in the horizontal and vertical directions, such as 800×600, 640×480, etc. The fineness of the image itself is only related to the resolution of the image itself. It is not related to the resolution of the hardware device processing it, but the fineness of the processing result of the image is directly related to the resolution of the device processing it.

Digital camera resolution

The resolution of the digital camera determines the size of the high-quality picture that the captured image can ultimately print, or the size of the picture that can be displayed on a computer monitor. The resolution of a digital camera depends on the number of pixels on the CCD (Charge Coupled Device) chip in the camera. The more pixels, the higher the resolution. It can be seen that the resolution of a digital camera is also determined by its production process, and it is fixed at the factory. Users can only select digital cameras with different resolutions, but they cannot adjust the resolution of a digital camera. For a digital camera of the same type, the higher the resolution, the higher the camera grade, but the high-resolution camera generates a large data file, which is high for the processing speed of the computer, the memory, the hard disk capacity, and the corresponding software. The request.

The level of the pixel level of the digital camera and the size of the photo that can be printed at a certain resolution can be calculated simply by the following method: If the resolution of the color printer is NDPI, the horizontal pixel of the digital camera is M, and the maximum printable photograph is M÷N. inch. For example, a printer with a resolution of 300 DPI and a digital camera with a horizontal pixel of 3600 can print 12-inch (3,600-300) image files without interpolating. Obviously, the larger the size of digital photos to be printed, the more digital cameras with higher pixel levels are required. The method of calculating the display size is the same as the method of printing the size.

Printing area resolution

In the field of printing, the resolution is expressed by the number of network lines per inch, ie, Lines Per Inch (LPI). In the traditional printing platemaking process, a screen is added before the original image in the making of a plate. This screen is composed of grid lines with transparent and opaque portions in a grid shape. These mesh lines are also gratings and their role is to cut the ray anatomy image. Because the light has diffractive physical properties, after the light passes through the mesh line, it forms points that reflect the changes in the original image image. These points are halftone dots. A halftone dot will not exceed the area of ​​one mesh at most. The more network lines, the more layers of the representation image, and the better the image quality. Therefore, LPI is used in the commercial printing industry to indicate resolution.

(to be continued)