A Short Course Book
Sensors, Pixels and Image Sizes

Exploring Pixels Per Inch

 
 
Click to open an Excel worksheet and use Part 3b. Printing Images-DPI to follow the instructions in this section.
Part 3 on the Excel worksheet "Pixels & Images Calculator" calculates the size of print you can expect from a given file size and the dpi you choose to print at. The numbers in the descriptions that follow refer to row numbers on the worksheet.

1. Width of image (in pixels) is where you enter the image's width in pixels.

2. Height of image (in pixels) is where you enter the image's height in pixels.

3. Desired width of print (in inches) is where you enter the width of the print you want in inches.

4. Height of print (in inches) is calculated so the print has the same aspect ratio as the image. The formula is in the form of a:b::c:d.

5. DPI (dots per inch) is calculated by dividing the width of the image in pixels (line 1) by the desired width in inches (line 3).

Exercises

Open the worksheet by clicking the Excel button in this section and enter numbers in the green cells to explore the questions that follow.

1. If you print a 4 x 6 image from an 1800 x 1600 file, how many dpi will there be along the long dimension?

2. If you print a 4 x 6 image from an 1800 x 1600 file, how many dpi will there be along the short dimension?



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