Determining Resolution

There is an estimated resolution of the human eye - it is 60 "photo cells" per degree of vision, or 60 cycles per degree of vision. A cycle is a black line next to a white line. In order to give the illusion that the image is not made from pixels, with the best vision in the world. you need provide 60 pixels per degree of vision. When cycles become a grey field - you have reached a resolution that gives the illusion of no pixels.

To calculate Resolution

1. determine the distance the viewer will stand from the image
2. determine the width of the image.
3. calculate the span in degrees of vision with Trig.
4. multiply the degree span by 60 (the answer is how many pixels wide the image should be)
5. divide by width in inches - the answer is how many dpi or ppi the image should be.

A 36" Viewing Example

1. 36" away
2. 12" wide
3. 20 degrees of vision
4. 20 * 60 = 1200
5. 100 dpi

A 12" Viewing Example

1. 12" away
2. 12" wide
3. 52 degrees of vision
4. 52 x 60 = 3120
5. 260 dpi

Practical Guides

postcards are 340 dpi
magazines are 300 dpi
posters and large artists prints are 150 dpi
I can distinguish between 150 and 300 at 8"

When you go the movies

This principle also applies to film grain. When you go to the movies, if you pick a seat that is as far away from the screen as (3 times the height of the screen) you will not be able to see the grain.

Joshua Mosley ©2002