The primary goal of outdoor advertising is to quickly grab the attention of your viewer and drive the message home with impact. You don’t have a lot of time to achieve these goals. Often your audience is speeding by in a vehicle, so you only have a millisecond to make your point. A brilliant idea can attract your viewer’s eye, but that’s often not enough. Making an image really sing requires a good dose of the right adjustments to make a huge difference in the brilliance and clarity of your image. The secret to a successful image lies not only in the concept but in the workflow that maximizes quality, color and contrast.

SCAN IT
No matter how you cut it, a good scan is essential to maintaining quality. Scan the image at a resolution that is consistent with your printer’s capabilities. In most cases, this means choosing a scan resolution of 300 ppi at 100 percent of the image size. If you’re printing from an image downloaded from a digital camera then be sure the image has enough information to produce a 300 ppi image when blown up to full size.
Low resolution images that are resampled up quickly lose sharpness and contrast, so be sure to collect enough information at the source to assure image quality. This might require an extra effort like shooting an image as a four by five film transparency and having the image professionally scanned at 8,000 ppi, or renting a high-end digital camera for an afternoon if you don’t have one.
If the image is color, scan it in 24 bit color. If the image is black and white scan it in 8 bit grayscale. There is not much advantage to scanning in the higher bit depths, unless you’re going to print a museum-quality image on an archival printer.

SET UP A HISTORY LOG
Photoshop keeps an ongoing record in the History palette of each state of your image, as you perform tasks and apply commands. The History palette lets you go back in time during the editing process to correct mistakes. Unfortunately, an image’s history is only active during a work session. When you close the document, the history is lost.
You can, however, save a record of all you do as metadata or as a text document and use it later as a guide to working on other images. In the General Preferences menu (see Figure 1), click on the History Log checkbox. In the Save Log Items to: field choose Metadata (to imbed the log in the image. You can access the metadata in the File > File Info > History dialog box. Choose Text File to save a text document of the History log to a specific location, or choose Both. In the Edit Log Items menu choose Detailed to create a detailed accounting of every command you apply.

CHOOSE A FORMAT
For large-format images I highly recommend saving the image as a PSB document. PSB format supports up to 300,000 pixels width and height as opposed to 30,000 pixels supported by the standard PSD format. Saving to the PSB format will enable you to work as large as is necessary.

MANAGE COLOR
Every image that will be output to a large-format environment needs to be color managed from the outset to assure accuracy throughout the image editing process. Utilizing the correct ICC (International Color Consortium) profile based on the output device, the ink set and the substrate is essential to assure the predictability of colors.
A profile is created using a color measurement device, such as a colorimeter, to first optimize monitor output and then using a spectrophotometer to measure printed color on the substrate. The color management software configures this data into a special text file. The profile is then loaded using Photoshop’s Color Settings dialog box (see Figure 2) and tells Photoshop how to re-map the pixel information to conform with the monitor and printing environments called the Color Working Space. When an image is opened into the color working space, or if a color correction is applied, the colors of the image conform to the gamut or color range of the target printer and substrate.

CROP THE IMAGE
If you have edges on your image that you are sure you want to discard, eliminate them at the beginning of the process. Doing so will produce a smaller file size and more accurate histograms. Furthermore, your eye will be less distracted by superfluous image elements.
Photoshop’s Crop tool displays a nice crop shield (see Figure 3) in your choice of color and opacity so that you can see exactly what your image will look like. The default is black 75 percent, but it doesn’t hurt to change it to white, 100 percent to display the image on a blank background before cropping. With the Crop tool, you can also rotate or distort the crop marquee, so that you can include exactly what you want in the picture.

MEASURE COLOR
The first step in color correction is to analyze the existing colors of the image. Hopefully, you have assigned the printer’s profile to the image because the numbers reflected in the two instruments that measure color, the Info and the Histogram palette will be affected by the profile.
A histogram is a graph composed of lines that show the relative number and distribution of tonal values within an image. From a histogram you can derive information about the tonal characteristics of an image. For example, a histogram devoid of lines on both the left and right ends of the graph indicates that most of tones are in the midtone range; therefore, the image lacks highlights and shadows and is of poor contrast, as in Figure 4.

The Info palette is the other color measurement instrument. It accurately measures the color of a single pixel or the average of a group of pixels. You can use the measured areas as markers when you make adjustments to the image. Specific areas can be marked with the Color Sampler tool (in the Eyedropper tool fly-out) and the pixel data appears in the Info palette, as in Figure 5. Since the palette is context sensitive, adjustments are displayed next to the original sampled numbers as adjustments are performed. Using one of the color adjustment features — to neutralize shadows or highlights by configuring equal RGB values — is a great way to eliminate color casts in the entire image.

ADJUST COLOR
The most common sequence of adjustments is to first apply Levels to increase contrast, then Color Balance to remove color casts, and finally a Curves to target specific areas of the image. All of theses steps can be performed accurately exclusively with Curves but the dialog box is formidable and takes practice to master.
Essentially, the color correction dialog boxes perform similar functions — they change the numerical value of pixels. How they perform their specific tasks depends on their focus. For example, Levels and Curves can both correct contrast and darken an image. Levels (see Figure 6) performs the task more globally having fewer adjustment points, while Curves (see Figure 7) with its numerous points of adjustment can more easily target a specific range of pixels.

USE LAYERS
Applying your adjustment through an Adjustment Layer (see Figure 8) provides several advantages. First, you can at any time revise the adjustment by clicking on the icon in the Layers palette to redisplay the currently configured dialog box. Another advantage is that you can adjust the global opacity of the adjustment with the Opacity slider, thereby mitigating it’s strength. Also, you can modify the location of the adjustment on the layer by painting on the attached Layer Mask. Paint with black on the mask to totally conceal the adjustment from a region, reveal it using white, or paint with gray to partially conceal it. Finally, you can apply an Adjustment Layer through one of Photoshop’s numerous blend modes to further alter the color.

SHARPEN THE IMAGE
With all adjustments in place, the final step in the workflow is to increase edge contrast by sharpening the image with the Unsharp Mask Filter. First, make a copy of the image (Image > Duplicate) and flatten the duplicate to assure that you keep your layered version, should you need it down the line.
The technique I recommend as being the most non-destructive is to duplicate the background layer of the flattened image and apply a Luminosity blend mode to the new layer to avoid color shifts. Then choose Filter > Sharpen > Unsharp Mask (see Figure 9). Apply an Amount (less than 100) and drag the Radius to increase the overall sharpness but not enough to produce halos and artifacts around the edges. Then apply the Threshold to restore the smoother areas of the image. Click the Preview button in the dialog box a few times to compare the results to the original.

BETTER LOOKING IMAGES
The steps outlined in this article are rules of thumb to assure accuracy and to enhance the color and contrast before you print. Of course, the specific settings you use will depend on your image and your printing environment. Give these basic steps a whirl, and you’ll be amazed at how much better your images will look. Don’t forget that Photoshop offers numerous other adjustments and filters that you should experiment with until you develop your own custom workflow.