Imaging Tip: Gaining Max Sharpness from Digital Camera Files

IMAGING TIP: Gaining Maximum Sharpness from Digital Camera Files
by Rich Seiling

If you are savvy about how you use sharpening, you can make big, sharp prints from digital camera files, despite their limited resolution. This tip will show you how to keep the edges of objects looking sharp, creating the illusion of better quality, even if there isn’t much resolution.

First off, let's discuss the difference between sharpness and resolution. When I talk about sharpness, I am referring to how well the edges of objects in your image are defined. Sharpness is different than resolution. Resolution is the amount of detail you can see in an object. While the two do work together, addressing them separately can deliver better quality.

There are two primary variables that affect sharpness, which you can control when making large prints from digital camera files: interpolation, and the applying of various sharpening filters (like Unsharp Masking). Interpolation and sharpening work hand-in-hand to affect the sharpness of the final print.

Interpolation

Every output device has a native resolution, which is the number of pixels it is physically able to print in a given length. For most Epson printers, this native resolution is 360 dpi, and for the Chromira, it is 300 dpi. This is important because, any time you send a file at a dpi lower than the native resolution of the output device, it will interpolate the file up to its native resolution before printing. Interpolating means the printer creates pixels, and usually this leads to the loss of sharpness in the final print.

Interpolating is a fact of life with digital camera files. Even the 16.6 MP file from a Canon 1Ds MK II will only make a print at 16.64 x 11.093 inches at 300 dpi without interpolation. If you want to print larger, you have to interpolate. The good news is that we can choose what software or hardware does the interpolation. Instead of letting the output device do the interpolating, we can interpolate in Photoshop, where we have more control. My testing shows that using Photoshop to interpolate files produces better results than the interpolation of the Epson or the Chromira.

When To Sharpen

Now that you’ve decided to interpolate in Photoshop, you can consider sharpening. There are three steps where you can apply sharpening:

In the Camera RAW plugin in Photoshop
After converting from RAW, but before interpolating
After converting from RAW, and after interpolating

For the best results, you should use all three. By varying the amount used at each stage, you can have almost unlimited control over the sharpness of your prints.

Here’s how to do it:

1. Open the RAW file in Photoshop.

You should be in the Camera RAW plugin, which lets you choose how to convert the file from RAW to a TIFF file. You should choose to create a file at the native resolution of the camera. This is accessed from the Show Workflow Options and the Size command.
The native resolution is the one that has neither a + nor a - after it. Photoshop lets you interpolate at this step with these + and - resolutions, but the best results are achieved by not interpolating at this step.
Add sharpness at this point, by clicking on the Detail tab and using the sharpness slider. My friend, Michael Frye, has recommended using a setting of +40, which works very well. This setting gives you a good base to work with in Photoshop. No amount of sharpening in Photoshop later can equal adding +40 sharpness at this step.
Once you have made these settings, you can make any other adjustments you feel necessary with the other tools available in Camera RAW.
When you are done, click the “open” button to bring the file into Photoshop.

2. Once the RAW file has been converted and brought into Photoshop, use Photoshop’s Unsharp Mask filter to sharpen your image to your taste. (This step happens at the Targeting stage of a Master File Workflow.) Sharpening is determined visually by looking at the effects on the screen, while viewing the image at 100% magnification. As a starting point, apply the same amount of sharpening as you would with your normal workflow.

This step gives you the most control over how sharp your final print will be. If your final prints look too sharp, or not sharp enough, you should change the settings used in this step before adjusting the settings used during Step 1 and Step 4.

3. Use Photoshop’s Image Size command to interpolate to the native resolution of your chosen output device. You do this by entering in the width and height you want for the final print, and setting the dpi to the native resolution of your chosen output device. I use the plain old Bicubic method of interpolation, but feel free to see what flavor the other methods of interpolation impart to your prints.

4. Interpolating always destroys some sharpening. We can bring some of this back by using the Unsharp Mask filter again, using a very low setting. Your amount will usually be between 30 and 100%, and a radius of approximately 0.3 to 0.5 pixels.

Loss of sharpness visible after interpolation

Unsharp mask of 100%, 0.5 radius, 0 threshold added after interpolation

Since this file has already had sharpening applied at steps 1 and 2, small changes in these values will have big effects. At this step, we are fine tuning, and the parts of the photograph most affected are the edges of objects. By making the edges look sharper, the photograph will appear sharper overall. With that done, you are ready to make a print and see how it turns out!

Practice Your New Skill

Now that you know how to take control of sharpening and interpolation, put it into practice. Make some test prints to learn what settings make prints that please your eye. You’ll be amazed at the amount of control you have, and the results of your efforts.

Summary of steps to achieve maximum sharpness in prints from digital camera files.

Open RAW file with Photoshop’s Camera RAW plugin. Choose the native resolution of your camera, and add +40 sharpening.
After converting RAW file, use Photoshop’s Unsharp Mask filter to sharpen to taste.
Use Photoshop’s Image Size command to interpolate to the native resolution of your chosen output device.
Use Photoshop’s Unsharp Mask filter to add a very small amount of USM to counteract the effects of interpolation.

This methodology was developed using a RAW file of 16.6 megapixels from a Canon 1Ds MK II, and printing on the Chromira and Epson 9600. While some settings are specific to this camera, the approach and methodology can be applied to most dSLR and prosumer digital cameras. There are no perfect settings, because every photographer has unique preferences and objectives.