Photograph Resolution - increasing?

isofa

I've worked in this industry for many years, and so many people don't understand the difference between pixel size and then input PPI and output DPI / LPI!

It's the amount of pixels the image contains that are crucial. You can adjust the output resolution to whatever DPI you want, then when outputting (printing etc) the higher the DPI the smaller the image will be physically on the paper.

This is not resampling. Resampling is changing the resolution and / or introducing detail which doesn't exist (pixellating the image making it larger than the original in pixels) and / or cropping the image down losing detai (and making it smaller losing pixels).

If you are using Photoshop, use the Image Size command and ensure the Resample Image checkbox is unticked. Then change the resolution of the image to what you require, you'll notice the pixel size doesn't change at all, but if you change the view / print size to cm or inches, you'll see this does. If you don't use Photoshop, try using the free applications such as: Paint.Net or the GIMP which both have similar options.

Most run of the mill magazines output at 200 to 250dpi in full colour, higher quality magazines at 300 to 350dpi. The paper quality is crucial. Newspapers are effectively 150dpi, (or 120 to 150 lpi) but I'm oversimplifying here - the screening is a key factor.

An image to be printed at full scale A4 (210 x 297mm) needs to be 3508 x 2480 pixels. However if you are preparing for pre-press / professional print, you'd need a bleed on this, so a few extra hundred pixels would be useful.

If you search on these forums you'll find some similar articles about print size and dpi. I imagine the Adobe website will contain some good help articles about this, and that'd be worth a look too.