Best File format for Printing

I have an image I've been working on in Lightroom saved as a .psd file. If I want to have an A3 print made, which would mean sending it to a printer, what is the best file format to save it as. Or does it depend on what the printer asks for

Check the specification required by the printer and provide them with the file that's optimum based on that.

Usually a JPEG is asked for.

It does depend.

JPG is usually required (because anything other can be massive).
Sometimes you need to output to a custom colour space profile, i.e. the colour profile of the printer. In that case, Lightroom allows you to output with a particular intent using an ICC profile.

(e.g. I have a "ProAM 18x12" setting in Lightroom that resizes the longest edge to 18 inches at 402dpi with ProAM Imaging's printer profile. Works a treat and saves a ton of messing in PS!)

Matt

As you may have gathered this is new to me.

When you save as a JPEG would you keep the original file size to retain detail for printing, or again would the printer specify the file size

Your pixel dimensions and ppi should deliver the size you want to print at, the JPEG will need to be maximum quality.

For example, it might be a 16" x 12" print at 300ppi, which is pretty much what comes out of a K-5 as is. Anything else, it will need resizing.

HI Barrie

From Lightroom, I right click the image. An export box pops up. I set the pixel dimension on the longest side to that suggested by the printer, and export it to my hard drive as a jpeg with sharpening applied for a print. I also apply the profile (either sRGB, or in my case as I use DSCL, their Lustre paper profile)

EDIT: As John mentioned I also select 300ppi

There are three main areas:

1. Pixel dimensions. These should be set to match the required print size and DPI(PPI) of the printer. If they don't specify, use 300dpi and pixel dimensions according to your required size.

2. Colour space. Most consumer print services expect sRGB - so use that in Lightroom. Some have specific profiles (e.g. ProAM)

3. Quality. This is how much compression is applied to the image when saving. The higher the quality, the larger the filesize. A quality of 90 is reasonable for print.

I'd recommend performing some test prints first before committing a large amount. When you have something that works, make that an export preset and you can just export away from there in LR.

Matt