Scanner Dust, Backscatter & the Dust That Adobe Forgot

A little Photoshop history—and a feature request for Adobe

Long before Lightroom, before Camera Raw became what it is today, and certainly before AI could remove distractions with a click, there was scanner dust.

It was the mid-1990s. I was working as a commercial photographer, shooting catalogs, advertising assignments and still working with both film and some of the earliest digital cameras. My film cameras included 4×5, as well as 2¼-inch formats.

When a commercial transparency was finished, the next step was often scanning it to produce a high-resolution TIFF.

And that's where the fun began.

Or, more accurately, where the dust began.

Even after carefully cleaning a transparency, there always seemed to be tiny pieces of dust or debris that found their way into the scan. On the resulting image they appeared as little black spots—sometimes hundreds of them.

The solution?

Zoom in, grab the Retouching tools and remove them one at a time.

For hours.

There had to be a better way.

Digging beneath the surface of Photoshop

This was back in the days when Photoshop had features and capabilities that weren't always obvious. I started digging into the program and discovered a rather obscure way of using History to accomplish what I wanted.

The concept was simple.

I could create a History state, apply a blur or Dust & Scratch treatment to the image, and then use the original image through the History Brush to paint back the information I wanted.

When the History Brush eventually became much more accessible in Photoshop's Tool palette and History panel, it was a revelation.

One brush could remove those annoying little black scanner-dust spots.

No more individually retouching every speck.

From technique to Action

By the late 1990s I was teaching Digital Workflow, with much of my teaching centered around Adobe Photoshop.

I eventually created a Photoshop Action I called Scanner Dust Spotting.

The Action used the Dust & Scratch filter with selected Radius and Threshold settings, created a Snapshot, returned to a previous History state, created a mask filled with black, selected the appropriate History state for painting, switched to the Brush tool with white paint—and stopped.

From there, the process was incredibly simple:

Paint over the black dust spots.

The Action did the heavy lifting.

Whew!

Then came the underwater problem

In the early 2000s I was asked to teach the Photoshop portion of an annual underwater photography workshop.

That's where I discovered that the same basic concept could solve a completely different problem.

Underwater photographers have another kind of "dust."

It's called backscatter.

Instead of black spots created by dust on a piece of film or scanner, underwater backscatter often appears as small white or light-colored spots throughout the image.

The cause is completely different: light from the strobe or other illumination reflects from particles suspended in the water and comes back toward the camera.

But visually, the problem is remarkably similar.

You've got hundreds—or sometimes thousands—of little unwanted spots scattered across an image.

My Scanner Dust Spotting technique could be adapted.

The trick was to reverse the tonal logic. Instead of treating the dark spots as the defect, I modified the process so that the light spots became the targets.

I eventually renamed that version the Backscatter Action.

And it worked remarkably well.

In many images, it could eliminate roughly 90 percent of the visible backscatter without requiring me to individually retouch every particle.

Fast-forward to Lightroom and Camera Raw

Today we have something completely different.

Adobe Lightroom and Adobe Camera Raw have sophisticated Dust/Distraction Removal capabilities that can identify and remove unwanted spots far more intelligently than anything I had available in the 1990s.

For traditional scanner dust—the little black dots—these tools can be fantastic.

But it got me thinking:

Why is there no "White Dust" option?

Or, perhaps more appropriately for underwater photographers:

Why not a Backscatter option?

The fundamental problem hasn't changed.

We're still trying to identify small, unwanted visual anomalies and replace them with information from the surrounding image.

The difference is simply the polarity of the defect.

Scanner dust:

Dark spot → remove it

Underwater backscatter:

Light spot → remove it

The technology exists.

The processing power exists.

The AI exists.

And Lightroom/ACR already has a feature called Dust/Distraction Removal.

So why not give photographers a simple choice?

Dust

• Dark Dust
• Light Dust / Backscatter

Imagine the possibilities

For underwater photographers, I could see this being extremely useful.

Select Light Dust / Backscatter, and Lightroom or Camera Raw could search for small, isolated bright particles that don't appear to belong to the underlying scene.

Perhaps Adobe could provide a few controls:

Detection: Low / Medium / High

Particle Size: Small / Medium / Large

Removal: Subtle / Standard / Strong

And, just as importantly, provide an overlay showing the areas the algorithm has identified before applying the corrections.

Because obviously, not every bright spot is backscatter.

A photographer wouldn't want the software removing stars, bubbles, fish, reflections, specular highlights or important details in the scene.

That's where intelligent detection and user control become important.

From History Brush to AI

Looking back, it's interesting to see how this problem has evolved.

In the 1990s, I was using Photoshop's History capabilities to find a way around manually removing scanner dust.

Then came the History Brush.

Then my Scanner Dust Spotting Action.

Then, working with underwater photographers, I reversed the process and created my Backscatter Action.

And now Lightroom and Camera Raw can automatically identify and remove dust and distractions.

We've come an incredibly long way.

But we're still missing one little checkbox.

What if dust isn't dark?

For underwater photographers, it often isn't.

It's white.

And perhaps it's time Adobe gave us a Reverse Dust / Light Dust / Backscatter option.

After all, I've been trying to get rid of these little spots for over 30 years.