The following general guidelines for image preparation will ensure that you get the best results from your images:
- A quality monitor that has been appropriately calibrated and profiled is essential. Recommended brands are NEC and Eizo. The following monitor calibration target settings are a good starting point for a reasonable monitor to print match:
- Brightness: 100 cd/m²
- Black Level: 0.4 cd/m²
- Gamut: Full
- White Point: 5500K (D55)
- Gamma: L* (if supported)
- If you’re an Adobe Photoshop Lightroom user, click here.
- For optimal results files should be provided un-resampled, namely at their original (camera or scan) pixel dimensions (less cropping). Resampling will either throw away information that the printer can use or bloat the file size unnecessarily. (If you have inadvertently resampled your images to a non-optimal 300ppi, don’t worry you’ll still get acceptable results.)
- If you require an exact size and layout, use Photoshop’s Image Size to set the image dimensions (with Resample Image unchecked, see below), then optionally Canvas Size to define a pure white border. (Equivalent options should be available in whatever software you use.) If you simply request a print at metric sizes (A4, A3, A2 etc) it will be assumed that your size requirements are approximate only.
- How big can an image be printed? A rule of thumb to figure out a rough print size for a given file is to divide the pixel dimensions by 240ppi (for digital) or 300ppi (for film) but anything down to about 180ppi can often deliver satisfactory prints. The actual results depend a lot on the quality of the pixels, subject matter (especially if it contains high frequency detail), print viewing distance, paper texture etc. The smaller you print, the higher the quality under close inspection.
- Choose a colour space at the time of rendering appropriate to the image colours (a more detailed explanation can be found here). Tag your file with this space when saving it (see below). Files that will be printed as B&W can be converted to a grayscale space (ideally with the same gamma) to reduce size. (Confused about colour spaces? Just leave it as is.)
- If you have important shadow detail in your image, use Photoshop’s Info panel and set the secondary read-out to Lab Color. (If you’re a Lightroom 5 user, in the Develop module right/ctrl-click on the Histogram and select Show Lab Color Values.) As you move your mouse over shadow areas observe the L value. Anything less than an L of 2 will print as black or near black irrespective of how it appears on your monitor. Edit your image to adjust such values upward accordingly. (Calibrating your monitor to a gamma of L* instead of 2.2 can give you a better portrayal of shadow detail.)
- Avoid clipping shadows and/or highlights in your image as this is detail that cannot be retrieved. The same goes for over-saturating images in smaller spaces which will clip individual channels. Photoshop’s Histogram panel will show you if clipping is present.
- Avoid over-sharpening as the results aren’t repairable. Some sharpening is generally required at capture time for both digital and film originals but this should be modest. Output sharpening, as required, will be applied prior to printing using routines developed in-house for optimal results.
- Finally, make sure you go over your entire image at a view ratio of 100% (Actual Pixels) to check for editing artefacts and blemishes from sensor dust, scratches, hairs etc.
- Files ideally should be provided as RGB (or Grayscale), TIFF, all layers flattened and at working bit depth but most files that Photoshop will read are OK. Files that contain vector content (text etc) should however be provided un-flattened. If your file is CMYK (for whatever reason) do not convert it to RGB. No un-rendered RAW files please.
If you have any questions regarding the preparation of your files, please don’t hesitate to ask