In the last few days I played some more with my new printer and made nice prints from this image and from the one below. And in that process I gained appreciation for master files — the most flexible format for storing an image.
A master file is usually a PSD-file that is virtually size- and media-independent. It allows you to produce web-sized JPGs or prints of any reasonable size in seconds. My master files are in 16 bits and in the ProPhoto color space. Source-sharpening and spot corrections are usually merged into the background layer and each major edit is on a separate layer. The name of each layer describes the function of the layer in a meaningful way. I haven’t done much creative sharpening, but if I did, I’d probably do it in a separate layer directly above the background layer. All changes necessary for printing also exist as layers, stored together in a layer-group named after the desired rendering intent. If I need different adjustments for different papers, I’d create separate layers (possibly in a separate layer-group).
A master file is very flexible because all major modifications are saved in separate layers. This way you can turn an edit on or off, change its parameters, increase or decrease its strength (by changing the layer’s opacity) or limit its effect (by adding a layer mask).
But in what way is a master file media-independent? Well, since it contains adjustments for different papers on different layers, with just a few clicks (by turning one layer on and another one off) you can target your image for a different paper. And if you turn all print-adjustment layers off, your image will be optimized for screen output. In fact, I save my master files with all print-adjustments turned off, so that they look optimally on screen.
OK you say, fair enough, but a master file has a fixed pixel-count. How can it be size-independent? Well, true, but the master file contains all perspective corrections, spot edits, source sharpening, etc, etc, so that if you need a file with a different pixel count, you simply resize a copy of your master file. Of course you will lose some quality, but this loss is inevitable, regardless if you are using a master file or not. The difference is that with a master file all the edits are already “inside” the resized image, so you resize, sharpen, and you are done.
The only disadvantage of master files is that they are large and require lots of RAM to work with, but somehow we are used to that nowadays…
And finally a word of caution: when you target your master file for a given size and media, be sure to save a copy and not the master file itself.