If you’re using Lightroom to process scans, it’s a good idea to create TIFF files that get the most from Lightroom’s processing power. Here are guidelines on the three most important aspects of a scanned file: color space, bit depth, and resolution. Paying attention to them before you scan really pays off during processing and printing.
Color space: Your scanner most likely has a setting for color space. Choose either Adobe RGB (sometimes called Adobe RBG (1998)), or if available, ProPhoto RGB, which is a very large color space similar to what Lightroom uses. This gives Lightroom the largest color space to work with during editing.
Bit depth: Bit depth refers to the amount of tone and color data a file contains. For color scans the usual options are 8-bit (sometimes called 24-bit) and 16-bit (sometimes called 48-bit). 16-bit files contain a huge amount of data when compared to an 8-bit file. This gives Lightroom more latitude when making tonal and color adjustments. But be advised 16-bit files are twice as big as 8-bit files and take more room on the hard drive. For example a 50Mb 8-bit scan would be 100mb 16-bit scan.
Resolution: Scanners allow you to scan at a variety of resolutions. The topic of resolution can be intimidating if you’re new to digital photography. I don’t have space to discuss the subject in detail here. But here’s what to think about when scanning:
If you plan to print something at the same size as the original print you’re scanning, choose 300ppi. For example, say you’re scanning a 4 x 5 print and you plan to create another 4 x 5 print, choose 300 ppi. That’s because 300ppi is a common resolution for printing so your scan will match the size of the intended output.
If you plan to make the final print larger than the original, double the resolution for each 2x increase in size. For example, if you are scanning a 4 x 5 print and plan to make an 8 x 10 print, doubling the dimensions of the original print (4 x 2=8, 5 x 2=10, 2×300=600), choose 600ppi for the resolution. This creates a larger file with more information used to upsized for 8×10. If you need a 16 x 20 (four times larger than 8 x 10), scan the 4 x 5 at 1200 resolution to facilitate increasing the size for 16×20 output.
Scanning film: If you’re scanning film, it’s important to choose the proper resolution. For example, if you are scanning a 35mm slide, the original dimensions are approximately 1.3 x 0.85. is 1.4 inches in length. It is highly unlikely that you will be making prints at the original size unless you are preparing a contact sheet. Because the scan will be printed larger than original, it’s important to increase the resolution when scanning film. To scan a file large enough to comfortably make an 8×10 print requires a resolution of 3000ppi. Many film scanners top out at 4000ppi so if you plan to make a large print like a 16 x 20, use this setting to get the most data to work with.
Considering file size: If you don’t know how you plan to use a scan in the future, consider scanning at a higher resolution to leave options open for future use. Just be advised that increasing resolution can seriously affect file size. A 16-bit 4”x5” file at 300ppi is a little over 10Mb. A 16-bit 4”x5” file at 1200ppi is a little over 164Mb.