Get Behind the Eight Ball

Geeks know that image file numbers divisible by 8 are easier for computers to process because of the 'architecture' are digital imaging. Just consider all the important numbers in digital image display to get an idea... all are divisible by eight.

When you are making digital images in PhotoShop® you can reduce or avoid invoking the kinds of anomalies created by averaging algorithms if you stick to numbers that your system likes... those divisible by eight.

The anomalies are spelled out in my book Giclée Prepress - The Art of Giclée (www.gicleeprepress.com) but it essentially boils down to avoiding 'odd' situations.

There are no 'odd' numbers in computer math. Digital imaging devices measure even numbers. If you give such a device less than the needed number of pixels the image must be scaled up to fit. If there are too few pixels, it must be scaled down. If the scaling involves numbers divisible by eight, everything 'fits'. But what if one number is an odd one?

Odd numbers force averaging that increases the odds that colors will shift farther from their original hues and shades. Suppose we have two pixels, one black and one white. If we scale up 100% and double that number to four pixels, the result is two black ones and two white. But suppose we scaled up to three pixels, what color would the odd pixel be? Gray... a color that did not exist in the original.

Although the best numbers for working in PhotoShop ® are divisible by eight, the best ones for your Epson printer are divisible by six. That is, when you set the resolution for the image the number should be divisible by six. Therefore, 240 is better than 220, 300 is better than 310, 360 is better than 380.

Creating originals with printing resolution in mind will help maintain the intended dynamic tone range and detail throughout the giclée production process. Similarly, setting the image for the correct printing resolution should be one of the first things done by the giclée prepress artist. Otherwise your printer may end up at 'sixes and sevens'.