How does darkroom software work?

[Jonathan Gingerich]

Okay, I was fooling around with my Elements 2.0 and realized I didn't really
know...

Say you have a digital photo 620x620 and you want to print it 3" by 3".
You tell the darkroom that you are going to set the printer to 300 b.p.i.
Now the software and the printer have to take 620 pixels and spread them
over 900 dots... I assume the software interpolates and de-aliases and
all that good stuff, invents another 280 pixels in each line, and hands the
printer a 900 x 900 matrix... Although I suppose the printer might physically
expand or compress what it's given...

Anyway, is there an advantage to printing at 600 b.p.i? Does the "extra"
room allow better interpolation affects? Is there a rule of thumb for this?

Thanks,
Jon.

[jaykinghorn]

Jonathan,

You have two separate elements at work here. You have an image file containing 620x620 pixels. If you print it at 3 inches square, the software now has roughly 203 points of information per inch. This is the image resolution, correctly abbreviated PPI. Obviously, the more information present in your original file, the larger print you can create. A rule of thumb for inkjet printers is to shoot for a file resolution of 240-300ppi at print size. Your 620x620 file would produce and optimum print between 2-2 1/2 inches. You can print your file at 3 inches, but the quality will suffer.

The DPI or dots per inch refers to the number of ink dots the printer sprays onto an inch of paper. The two numbers are not correlated in any way, although there are some combinations that produce ideal results. Using a greater number of dots per inch tends to give smoother transitions and cleaner edges. For printing photographs, I recommend using 1440 dpi.

best of luck,

Jay Kinghorn
RGB Imaging