How to set the resolution for scanning pictures
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When scanning a picture, how to choose the right resolution is an important and confusing question. Because it is not only related to the original and output requirements, but also directly affects the output. The scanning resolution is set low, and the output picture accuracy is not ideal; if it is set high, not only the effect cannot be displayed, but also the scanning and processing time is wasted, and the generated file is too large, which takes up disk storage space unnecessarily.
So, when scanning a picture, how do you choose the right resolution? This is determined by considering the original image size, final output mode, and output format.
Display on the screen
If images are only displayed on the screen (such as electronic photo albums, web page images), they are equivalent because the scanning resolution is directly converted to display resolution. The screen can only display about 72dpi (dpi is Dot) Per The abbreviation of Inch, which is the number of dots per square inch, is so large that it can be displayed with a resolution of 72 dpi. Using a higher resolution will only increase the amount of image file data and display area, and will not improve the sharpness of the image displayed on the screen.
Print out with a printer
The scan resolution is not the same as the resolution of the printer. The size displayed on the screen is not the same as the size actually printed. The resolution represented by a color inkjet printer refers to the output precision of various colors, and dividing it by the number of colors is its effective precision. If the nominal resolution is 720 or 1400 Dpi four-color printer with effective resolutions of 180 and 350 respectively Dpi. Therefore, when the original large print output, the scan resolution is only equal to the effective accuracy of the printer. That is, scan resolution = printer resolution ÷ printer nozzle color number.
For color printing
The print resolution indicating the printing accuracy is different from the resolution of the electronic image. It is using lpi (Line Per Inch's abbreviations). That is, the number of output lines per inch. The newspaper is about 85 lpi, the color magazine is about 150 lpi, and the art book and fine art books may use 300 Lpi. When scanning images are used for printing, the resolution needs to be determined according to the accuracy requirements of the printing. An easy way to set the resolution at the original large output is to multiply the number of lines (lpi) of the printed output by 2. Therefore, the best scanning resolution for newspapers, magazines, and art book printing should be 170, 300, and 600 dpi, respectively.
All of the above are the original big output. To scale the output, you also need to multiply the scaling factor. The scaling factor is equal to the output size ÷ original size. Therefore, the setting of the scanning resolution depends on the output device: for the screen display = scaling factor × 72 Dpi; for printout = zoom factor × (resolution of the printer number of print heads of the printer); for printing = scaling factor × (number of printed lines × 2). As can be seen from the above calculations, the smaller the original image, the higher the resolution of the printer and the larger the output format, the higher the scanning resolution required.