So if you’re scanning negatives or transparencies, you may have a specific size print that you want to create. For example, I’ve been scanning a lot of 6×7 transparencies lately. I want to print them large, like 24″x30″, so how do you scan it to get the best possible print?
First you need to know the printer’s resolution. The service that I use has printers that output at 250dpi. Most printers that I’ve seen are in the range of 240 to 360dpi.
Second, you need to know the size of the image you’re scanning. My 6×7 transparencies/negatives are usually around 2.2″ x 2.7″ in their respective dimension. It really depends on the crop that you’re scanning.
Lastly, we need a formula:
scanning dpi = (printer dpi * desired size) / current size
So in the example above we’ll choose one of the dimensions, and plug that value in:
scanning dpi = (250 * 30)/2.7
scanning dpi = 2,777
Maybe you can set your scanner to a dpi of 2,777, maybe you can’t. You should strive to set it as close to that value as you can.
Go ahead, scan your image now. I’ll wait………
OK, the last step is to resize the image in Photoshop. Reason being is that we now have an image that’s something like 6000×5000 pixels, but would print up as a 2.2″x2.7″ print. Not what you wanted, is it? Go and open the image in Photoshop and click Image – Image Size. In the Image Size dialog, deselect the Resample Image check box, then enter the printers dpi into the Resolution field. After you do this, you should see the Document Size change to be close to your desired print size.
Just so you know, I’m using an Epson Perfection V700 scanner, with Silverfast SE scanning software. My scanner can scan up to 12,600dpi, but I’ve read that it works best scanning at 6,400dpi. I’ve been scanning my stuff at 2400dpi, and that gives you an image around 200MB, with a dimension of 6,542×5,213. This would print a real nice 24″x30″ print.