Digital Tips Page - fine art photos by jim coe, Everyday Magic!

Before	After

Typical Digital Photo Chores:
My "Before" image is a 35mm slide digitized to a Kodak Photo CD. Besides my less than perfect original, the conversion created some common problems. The gamma is off because this consumer quality CD was designed for viewing on a television. The sharpness is reduced by the digitization process used. The color is also off. Fortunately, the quality of low priced Photo CD digitization has improved since this slide was scanned in 1995.

Anyway, this is a typical set of normal cleanup and fix up chores. The idea is for you to bring the image back in line with what you saw and photographed, without being heavy handed. If you do too little, the problems won't be fixed. If you go too far, the final image won't be true to whatever happened between you and the subject. Either extreme can only weaken any expressive power carried in your image. Can you see why these image chores are best done by the photographer who made the image, not left to others?

So, here we go....
First, you do the standard chores that you would also do with manual photography.

1) I "spotted" the image to remove dust specs, scratches, etc. A Rubber Stamp tool is great for this - much nicer than manual print spotting!

2) I cropped the frame to improve the balance and remove redundant areas ("anything that doesn't further the image hurts it").

My next tasks are either much easier on a computer than in a darkroom, or simply impossible without digital tools.

3) I modified value curve to give darker shadows, also strengthening the wall texture and improving the highlights. You can roughly control contrast in a darkroom, but it's pretty much all or nothing. With digital value curves, I can get different contrasts (slopes) in different areas of the same curve. In other words, in one photo, I can treat the shadows one way, the mids another and the highlights a third. In this case, I darkened the shadows, left the mids alone and lightened the highlights.

Note that this is not really the same as just adding contrast, because I control all regions of the curve pretty independently. I can create higher contrast in one part of the curve and, at the same time, lower contrast in another. Then again, i can mask an area of the image and change the curve for that area only.

4) It was pretty easy for me to shift the color balance back toward the original scene. Here again the digital tools are faster, less expensive, easier to use and give me more control. For example, in Adobe Photoshop, I have individual curves for each of the three color channels.

5) Next, I reduced the image in size and resolution to fit Web browsers and a typical viewer's monitor.

6) Then, I carefully sharpened the image. Sharpening an image is only possible digitally.

7) Finally, I converted it to JPEG format to make it compatible with Web pages and to compress it for faster Internet transmission. The "After" photo is the end result. Do you agree that it's an improvement - without over-doing it?

Using a fully digital camera in the first place would eliminate some of these chores. But even then I would want to enhance my images. Then there's my big old slide collection....

Getting the Goodies - Without Paying the Price:

Fig. 1 - Original	Fig. 2 - Sharpened in RGB	Fig. 3 - Sharpened in LAB

How to Sharpen Images With Fewer Nasty Artifacts:
One of the most commonly used digital fixes is the sharpening filter. As my friend the Mathematician used to say, "Every filter function leaves its fingerprint on whatever passes through it - that's just part of how things work." The sharpening filter can leave a very nasty fingerprint, as shown in Figure 2. This is a (exaggerated here) use of the Unsharp Mask filter in Adobe Photoshop on the photo in Figure 1.

The Unsharp Mask filter fakes added sharpness by making one side of all edges lighter and the other side darker. When done subtly and viewed at the normal image size, this makes the image seem to be a lot sharper. Of course it isn't really sharper, it just takes advantage of the way human visual perception works to fool us. But the price you can pay for using this valuable trick is unwanted side effects. Notice that in Figure 2 (for example inside the red lines) the Unsharp Mask is actually changing the colors! Even the texture of the plaster wall now has new colors. How bad these artifacts look depends on the particulars of your image. Some images aren't too badly hurt by this, while others are ruined.

Here's how to get the benefit of sharpening filters in Adobe Photoshop without paying off in colored artifacts. Before you sharpen, or apply other effects in which you don't want accidental color changes, convert the image from RGB mode to LAB mode. You can go back and forth between these two modes as often as you like, with no penalty. LAB mode has the effect of separating your image into two color-only channels and one monochrome channel. In effect this lets you remove the colors, so they aren't damaged, do your processing, then put the colors back again! Once in LAB mode, just turn off all but the L channel and your processing can't change the colors. Be sure to turn all the channels back on and convert back to RGB mode when you are done.

Figure 3 was processed exactly like Figure 2, but the Unsharp Mask filter was applied while the image was in LAB mode with the A and B (color) channels off. Notice that in Figure 3 the Unsharp Mask effect works just the same, but the colors aren't changed. I'm sorry that the differences between figures 2 and 3 are not as easy to see on a Web page image as in the originals. However, I think you can still see the differences.

I highly recommend using LAB mode to protect your color information during critical digital filtering operations.

My thanks to Dan Margulis and Computer Artist magazine for his very valuable "MAKEREADY" column. I learned about LAB mode from one of Dan's recent columns. Check out his writings for first rate image processing info.

Notes:

Information on Dan Margulis, his writings and his services can be found here.
Dan Margulis has a new book out: "Makeready, a Prepress Resource" from MIS:Press.

Information on Computer Artist magazine can be found here.
Computer Artist magazine: Penwell Publishing Company, Subscription Offices (918) 831-9405

Please see my Photo Links for more off-site resources.