What is the relation between pixel size, physical size and DPI resolution?

Some viewers count on the DPI to calculate the image size in inches (such as for printing purposes or distance measurement). You can call the size calculated this way the 'physical' size if you will, since it usually corresponds to the size in inches for a scanned page.

For example, a letter-sized page scanned is 8.5x11 inches. If scanned at 200 DPI, the resulting image would be 8.5*200 x 11*200 which is 1700x2200 pixels.

The general formula that's always true is pixles = DPI * inches.

When we say that we want to change the DPI to 300 for example, the important questions is:
Do you want to preserve the physical size (in inches) or do you want to preserve the bitmap size (in pixels)?

If you want to keep the physical size, you must resize the bitmap pixels so that the ratio (inches = pixles/DPI) remains fixed.

If you want to keep the pixel size, you do not resize the bitmap. You simply change the number that represents the DPI in the image header.

Different programming interfaces in LEADTOOLS allow you to perform both of these tasks. For details, refer to the documentation or contact our support team at support@leadtools.com.

Edited by moderator Wednesday, December 27, 2023 2:27:08 PM(UTC)  | Reason: Not specified