I’ve been doing some consulting recently, helping a designer prepare photographs for a personal history print book. The photos are quite old, from World War II. This is the designer’s first exposure to photo preparation. He is changing careers. Although he is learning the techniques rapidly, this will be a trial by fire due to the work needed. My task is to teach him what he needs to know and oversee the photo manipulation.
The Process of Optimizing Photos
I have suggested that the designer (let’s call him Bill) follow a protocol to make photo preparation more routine. This should speed up the process, and make it more intuitive. After all, there are a lot of photographs to process.
I suggested the following workflow.
- Change color space from “RGB” to “Grayscale.”
- Scale and crop photo to final reproduction dimensions.
- Ensure that photo is 300 dpi at final size.
- Use cloning tool to correct small imperfections, such as dust spots.
- Adjust levels or curves to ensure a wide range of tones.
- Lighten the photo slightly to compensate for dot gain.
- Use unsharp masking in the filters menu to sharpen the image.
I read once that this series of steps would correct most problems with almost 95 percent of the photos a designer will need to manipulate.
I would add one further approach to the photos, given the massive number for this particular print book. I call it “triage,” from the medical term referencing the decisions for treatment based on the severity of the wound. If you are preparing photos for a brochure, this will be less important, since you will probably have only a handful to correct. But you have 50, 100, or more photos, it will be important to decide whether an individual photo is worth correcting. If it has major flaws (not enough tones from the lightest lights to the darkest darks, tears or scratches across faces or other detailed portions of the image, and so forth), you will need to invest a huge amount of time in a single photo. If you are batch processing 50 photos, you can’t necessarily afford to get stuck on one photo. You need to ask yourself whether it’s worth fixing the photo or whether it is a better use of your time to find another.
So to expand a bit on the photo processing list, here are some thoughts:
Color Space
Normally you will receive digitally scanned photos in RGB mode. However, if you will hand them off to a digital or offset commercial printing vendor, you will need to convert the images to CMYK (4-color process). To allow for the best reproduction, it’s best to keep images in RGB mode until the end of the process and then convert them to CMYK. On the other hand, if you will be producing black-only halftones (which is what my client is producing), change the color space from RGB to Grayscale first. You’ll get a clearer view of what you’re doing, since images can look very different in black and white than in color. The grayscale command is in the image menu under “mode.”
Scale and Crop
It’s best to come at least close to the final size and cropping when you place a Photoshop TIFF image in InDesign. And remember to avoid (like the plague) increasing the size of an image.
Resolution
Assume that you will need twice the custom printing vendor’s halftone line screen’s worth of pixel information in a photo. If your printer is using a 150 lpi line screen for halftones, make sure your photos will be at 300 dpi resolution (at the final printed size). Otherwise pixels may be visible.
Cloning
Use the clone tool in the vertical menu on the left side of the Photoshop pasteboard. It’s called the “clone stamp tool,” and it is about halfway down the series of tools. On the top horizontal menu, look for “opacity.” If you’re worried about damaging the photo, you can work gradually to correct flaws by reducing the opacity of this tool. Option click on a spot you want to use as source material to cover a flaw. Then point the cursor at the destination (the flaw) and click and draw. You will be drawing with the pixels you had selected, effectively covering the “destination” area with the “source” pixels.
Levels and Curves
Books could be written about these tools. Research them on the Internet. Your goal should be to give an image a wide selection of tones from black (if you’re working in grayscale, like my consulting client) through the dark grays, mid-tone grays, light grays, and white. Avoid abrupt changes in tone (they appear as spikes in the “histogram,” a graph that shows how many pixels of each grayscale tone a photo contains).
Lighten for Dot Gain
Ink spreads on paper as it flows into the fibers. In addition, your LCD monitor will make photos appear lighter than they will print. So compensate a bit by lightening your photos prior to handing off your job to your custom printing supplier. If you have any concerns, send sample photos to your printer and ask for advice.
Unsharp Masking
Unsharp masking (found in the “filter” menu under “sharpen”) makes images appear sharper (less blurry) by accentuating the tonal difference between light and dark pixels. Too much adds artifacts and halos. This looks painfully bad. You have three variables for unsharp masking: amount, radius, and threshold. Check online for starting values (i.e., amount: 75, radius: 1, and threshold: 10, as noted in one online tutorial by Simon Mackie for “soft subjects”). Experiment. If you see graininess or halos, you’ve gone too far, so back off.
Then save the image as a TIFF file.
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on Tuesday, January 29th, 2013 at 7:48 pm and is filed under Photos.
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