Maybe it’s just because I’m in the midst of de-rusting and repainting my VW bus, but it seems to me that a lot of the routines I go through to make my digital prints sing are a lot like painting and polishing a car—cleaning off all the dust, making sure the paint’s blemish free, touching up the pinstripes, giving the chrome one extra coat of wax. It’s those small, almost subliminal, touches that make an ordinary auto stand out.
A lot of my photo manipulation techniques serve the same function. They don’t fundamentally change the photo- graph, but they get me a much better print of it. It’s likely you’re
already familiar with one or more of the methods I present in this article, but I’d be surprised if you’ve tried all of them. I use them so regularly that I don’t ever make a print that hasn’t ben- efited from several of these rituals. These routines are indeed, well, routine, but that doesn’t make the results any less special.
Unless your technique is truly immaculate (and you are very fortunate), there’s going to be a certain amount of spotting that goes with your digital printing. Unlike physical-print spotting, a digital photograph only requires spotting once, but you really want to get it right so that every print looks clean. Whether you’re scanning film or capturing digital images directly with a DSLR, dust will pay a visit. It’s a much worse problem with film scans, though few digital photographers have made lengthy field trips and not discovered that a certain amount of dust worked its way onto the camera sensor during lens changes.
The very best tool I’ve found for dealing with these unwanted guests is Photoshop’s Dust and Scratches filter, selectively applied with the History brush. It’s many times faster than using the Clone tool or the Spot Healing brush. I’ve got a trick for using it even more efficiently that you won’t find in most of the books.
To clean up the dirty film scan shown in Figure 1a, I used the Dust and Scratches filter settings shown in Figure 2 to create Figure 1b. I set the Radius large enough to wipe out the largest dust specks and do a good job of obliterating scratches. The precise set- ting isn’t very important—the Threshold setting is another matter. Look for a “sweet spot” where most or all of the bad stuff is gone but the film grain isn’t completely suppressed. It’s OK if it’s softened considerably, as shown.
After applying the filter, assign the History brush to that filter state, then revert to the previous history state. Now here’s the trick: don’t use the History brush in Normal mode to spot out the dust. Instead set it to Lighten or Darken mode (Figure 2). When I’m working from negatives, I set the brush to darken because almost all the garbage is light. If I’m spotting slide scans or digital captures, I set the brush to lighten because almost all the specks will be dark. If the image has a mixture of both light and dark spots, I make one pass using the brush in Lighten mode and one in Darken mode.
The Lighten or Darken brush modes have much less effect on grain, background noise, and real subject detail than Normal mode. You can filter more strongly, set the brush radius wider, and paint over more specks in one stroke without distorting the underlying image or visibly altering the “texture” of the photograph. Figure 3 shows the results. Every photograph I print digitally gets cleaned up this way.
You’ll find that this method doesn’t work well if the speck you are working on is right next to a sharp edge or in an area with lots of fine detail. It also won’t catch the really faint scratches or specks that are barely above the noise level of the image. For those types of artifacts, use the Clone or Spot Healing tool.
De-graining and de-texturing
The Dust and Scratches filter is good for more than gross cleanups. Used with delicacy, I’ve found it a valuable tool for smoothing out grain and image noise in large prints. Generally, people aren’t bothered too much by uniform grain; what grabs the attention in an unpleasant way are the sharp fluctuations caused by clumps of grain and electronic shot noise (Figure 4a). These extremes stand out from the background. The Dust and Scratches filter can “shave off” those highs and lows in parts of the image that have little or no sharp-edged detail, such as large areas of sky.
Create a mask to select the area you want to work on. Don’t worry if it includes a few sharp-edged details that you wish to preserve; you can recover them later with the History brush. Set the filter controls for a radius that will obliterate the small dust specks but not the large ones (Figure 5). Use a threshold setting that is just at the point where the grain is slightly smoothed out. Use a very light touch on the setting; don’t set the threshold so low that the smoothing is obvious. You just want to trim off the extremes. If you smooth out the grain/noise too much, the difference in texture between the filtered and unfiltered portions of the photograph will make viewers notice your alterations.
This can eliminate about half the spotting you need to do in the filtered area, and smooth out the grain a little bit without it being obvious (Figure 4b). If there are a few details (like clouds or birds) that have edges that need to retain their sharpness, use the History brush to paint over those edges with the unfiltered state from just before you applied the Dust and Scratches filter. That will restore what the filter wiped out.
Many folks have noted that digital prints often (if not always) lack the subtle tonality and fine gradation of traditional prints. My guess is that it has little to do with the camera, as I have observed it in prints from photographs made with a Phase One 22-megapixel camera-back and in prints from my film scans. I believe it has more to do with the 8-bit printer drivers and RIP engines. (As we get fully16-bit native devices we’ll see if I’m right.)
Until then, subtle local variations in tone and color—“texture” or “snap,” if you will—seem to get suppressed (Figure 6a). Bill Atkinson taught me a nice fix for that, sometimes referred to as “local contrast enhancement.” It works so well and easily that I now use it on every photograph I print.
Pull up Unsharp Masking (Figure 7). Set the Amount for somewhere between 8 and 15%, depending on taste, subject, and printer (I used an abnormally strong setting for the illustrations in this article to make the effect clearer). Set the Radius for around 60 pixels (this value isn’t critical) and the Threshold to 0. Subtle tonal and color differences get enhanced just enough to make them look normal without a commensurate increase in overall contrast. It’s almost miraculous (Figure 6b).
Why this works: Unsharp Masking increases the difference between the target pixel and the surrounding pixels. A small Radius only affects boundaries where there are both bright and dark pixels nearby. There it makes the bright pixels brighter and the dark pixels darker than the average, exaggerating edges to make the picture look sharper (film developers do the same thing chemically, by the way).
Apply Unsharp Masking with a very large Radius and it doesn’t see edges; it sees the average tonality over a broad area. If the target pixel differs from that average, it increases the difference by a small amount. Slight local variations in tone, color, and texture get amplified. The resulting print looks livelier and has better tonality and gradation.
There is usually a slight increase in the value range of the photograph because the deepest shadows and most extreme highlights are frequently small areas that fall within the 60-pixel radius. Apply this filter before fine-tuning the image tone and contrast. I prefer to do it very early in my workflow, right after I make my gross tone-and-color adjustments, because I want to see this improved gradation while I’m performing other manipulations of my photography. When I make gross adjustments, I take care to have no pixel values below 20 or above 240, to leave sufficient tonal headroom for local contrast enhancements to do their work without clipping off shadow or highlight values.
Sharpen and smooth (or vice versa)
In the September/October 2006 PT, I reviewed two Photoshop plug-ins, Focus Magic (for sharpening images) and Neat Image (for reducing noise). Lately, I’ve taken to using them together to fine-tune the sharpness and graininess of my photographs. (Photoshop’s own Smart Sharpen filter works just as well for this, as do other noise reduction utilities.)
Applied with restraint and modest strength, these two tools balance each other off nicely. Sharpening has the side effect of increasing grain and noise, while noise filtering can compromise sharpness and fine detail. The proper mix of the two can sharpen an image without increasing its noise, or reduce the noise in a photograph without losing sharpness. Most often, I split the difference and get a photograph that is both sharper and less grainy, as in Figure 8. I find this most useful when making larger prints from high-resolution images.
Note that this is not sharpening for output, although it can reduce the need for that final step. This just brings out the most information in your photograph while minimizing the noise.
Restraint is important. Excessive noise reduction also tends to remove subtle differences in tone and color. A heavy dose can produce a grainless image, but surfaces look like molded vinyl, without subtle texturing. Sharpening up that image just makes the edges very well defined, with the result that the whole photograph looks even more plastic.
My method is to first run Focus Magic (Figure 9). I use a Blur Width of only one or two pixels. Normally one pixel is sufficient; if it’s a very high-resolution scan, two pixels may work better. Don’t go beyond that because you’ll see ringing at the edges— those bright and dark halos that announce to the world that you’ve sharpened badly. Leave the Image Source set to Digital Camera unless the image is extremely noisy, in which case choose Conventional (Film) Camera.
The resulting image will have improved detail, but also increased grain and noise. Sharpening tools, such as Focus Magic and the Smart Sharpen filter, indiscriminately enhance any fine detail, so your photograph gains noise at the same time that it gains sharpness. The next step is to suppress that enhanced noise.
For slight noise/grain suppression, I find that Neat Image’s default settings work very well with one important exception. The Y Noise Reduction Amount defaults at 60%. This almost completely eliminates grain and noise, but it also suppresses fine tonality, trending towards that abhorrent plastic look. All I want to do is kill the excess grain I got from sharpening. After one-pixel sharpening, a 25% reduction setting in Neat Image seems to work best. After two-pixel sharpening, 30 to 35% works best (Figure 10). This produces the balance I mentioned between somewhat improved sharpness and somewhat reduced grain/noise (Figure 8, lower right).
If I want to emphasize sharpness over noiselessness, I sharpen with a two-pixel radius and use the 25% noise reduction setting in Neat Image. If, on the other hand, I want to suppress noise without noticeably altering sharpness, I use a one-pixel sharpening radius and a 30 to 35% noise reduction level.
Selection masks or the History brush let you apply different effects to different parts of the photograph. For large sky areas, you might want more noise suppression; for sharply defined subjects in the foreground, increased sharpness may be more important. Since the changes are subtle, you don’t have to worry about applying different effects to different parts of the picture. The local differences won’t be apparent to the viewer, just the total aesthetic impact.
The Smart Sharpen filter has an advantage that it can be applied selectively to the Luminance channel in a Lab image (neither Focus Magic nor Neat Image work in the Lab color space). Working on the Luminance channel alone lets you improve sharpness without exaggerating chroma noise and getting little colored sparklies along edges. It’s good for particularly noisy and uncooperative photographs. Apply it at the 100% level with a radius of one to two pixels to remove lens blur, with “More Accurate” checked.
That’s it for polishing digital prints. Now it’s time for me to go mix up some more fiberglass resin and patch a few more rust spots on that bus of mine. If only I could simply tweak a few settings and hit a Fix button.