How to determine the dpi of a picture by scanning a picture

First, to calculate the correct resolution, you must consider three factors: 1. The number of screen lines printed last; 2. The size of the original image; 3. The size of the later image.

2. As long as you calculate according to the following steps, you can find the answer you want: multiply the length of the longest side of the last image by the number of screen lines, and multiply this number by the number of screen lines. The ratio (typical ratio is 2:1). metaphor:

• Suppose you are scanning an image that is 5 inches wide by 10 inches high. In the end, the image you are going to make is 8 inches wide by 12 inches high. The number of printed screen lines used is 150.
· Take 12 (the longest side of the last output image) × 150 (the number of printed screen lines), the result is 1800pixels; then multiply 1800 by 2 (the ratio of screen lines), the result is 3600pixels, which is The total number of pixels required.
• Divide 3600pixels (the total number of pixels required) by 10 (the longest side of the original image) to get a 360dpi scan resolution.
Different color separations may require different pixel/network ratios. It is best to ask your output center or printer for the best resolution before exporting.

Third, newspapers, fast printing printing screen line is usually 80-120, the general printing screen printing line number is usually 120-150 coated paper, advanced printing screen number is usually 175.

Source: PACK.CN