Scanning Slides, Negatives, and Photos:
introducing film and flatbed scanners

Scanning slides and/or film negatives gives new life to our film photographs. This analog to digital conversion allows us to enter images originally captured on film into the digital photography workflow, and assures that our older images will not be forgotten. This is becoming increasingly urgent, as traditional wet-process photo finishers decrease in number.

Scanners available today are inexpensive, versatile, and highly capable. All-in-one printers available for home use often incorporate a scanning surface with a copier. Indeed, a flatbed scanner is, at its most basic, a high resolution copy machine (the difference: a scanner produces a digital file, the copy machine a paper copy).

Those of us scanning slides or negatives, however, demand more than that. Millions of precious images are waiting to be digitized, and rescued from the ravages of time! Fortunately the technology has kept pace with demands for more flexibility and resolving power, to the point where there are now phenomenal scanners on the market for less than the cost of a good camera lens. I'll tell you what you need to know to get started right here!

Once you get beyond the basics, you'll discover that scanners are great for creative photography, a kind of desktop macro photography camera, in fact. Visit the Flatbed Scanner Photography page to explore the possibilities!

Types of scanners

The average user has a choice of two basic designs for scanning slides:

Flatbed scanners. So-called because of the flat glass surface onto which a paper original is placed for scanning. Most all-in-one printers available today include basic scanning capability along with copying and printing.

Scanning slides, however, requires a flatbed scanner that can scan transparent as well as reflective materials. This is accomplished by building a light source into the lid that is covered by a removable white cover slide. Cover in, scan reflective materials, cover out, scan transparent materials. Special film holders are provided for 35mm slides; some scanners come with holders for negative strips, medium format, and large format film material.

These scanners represent the ultimate in scanning flexibility and are phenomenal pieces of equipment. They are the tool of choice for artistic scanner photography (yes, there is such a thing: find out about it on this page!).

Dedicated film scanners are designed to scan transparent materials only. More compact in design than flatbed scanners because they lack a glass scanning surface, film scanners accommodate mounted slides; some allow scanning negatives on strips as well.

Film scanners feature high scanning resolution, with the advantage over flatbeds that they lack a glass surface between scanner head and original for ultimate sharpness. Some are available with bulk-loaders to handle big slide scanning jobs.

How do scanners work?

All scanners operate as a device connected to a computer. Dedicated scanning software (delivered with your scanner) allows the two machines to communicate.

A scanning head (containing a light source and a small digital sensor) passes over (or under) the original, reads the image and converts it into a digital file, which can be named, enhanced, copied, and moved around like any other digital file.

By slowly passing a small sensor over the original, scanners work around the issue of digital sensor size that drives our choice of digital camera.

While the price of digital cameras is in large part determined by the size of their sensors, scanners don't have that constraint. Because they bring the sensor to the source, scanners can create high-resolution files (exceeding the resolution from even full-sized sensor cameras!) without costing an arm and a leg. The trade-off is size and portability: scanners need space for the mechanics that move the scanner head and are not designed to be portable.

Scanner terminology

Here are some of the terms we use to compare the capabilities of different scanners, as well as the settings we use for particular scanning projects:

Resolution. Measured in dots per inch (dpi) or dots per cm (dcm). (see the Photo Resolution page for more on this important but potentially confusing topic).

Scanning resolution is adjustable in your scanning software, which gives us tremendous flexibility but forces us to decide on an optimal resolution number. My advice is to think backwards: decide on how the scanned file will be displayed and set resolution accordingly.

To review: display size is determined by the image size (number of dots) and by the display resolution. Computer screens display at around 100 dpi; prints at around 300 dpi (lower for larger prints due to increased viewing distance, see the Digital Photography Printing page for more). Commit these numbers to memory and you'll thank me later!

Let's say your goal is to create 4 x 6 in (10 x 15 cm) prints from a 35mm slide or negative. 35mm originals are 24 x 36 mm in size, or about 1 x 1.5 in. That means we need 1200 total dots in the short dimension to display 4 in. at 300 dpi (4 x 300 dpi = 1200). The same file, if displayed full-size on a monitor, would be 12 x 18 in (1200 ÷ 100 dpi= 12).

Scanning photographs that will be reprinted at the same size as the original? Scan at 300 dpi, and you're golden!
When scanning slides and negatives from fine-grained film, there is a practical upper limit of about 3000 dpi. At higher resolutions we're only scanning film grain, not adding additional image information. At 3000 dpi, files made from slides or negatives display at a whopping 30 x 45 in. on a monitor. They also create prints of almost any size we desire without pixelation.

The trade off with high resolution files is increased file size and slower scanning speed. This is important to consider when scanning slides in bulk. At my day job, we've scanned thousands of slides at 1200 dpi and have been pleased with the results.

Bit depth. (visit the Bit Depth page for more detail on this topic). Scanned files can be created as either 8-bit or 16-bit color files. Why, then, do we see scanners advertised as 24- or 48-bit capable? Because of the three color channels red, green, and blue (RGB): file bit depth multiplied by three!

In theory, a 48-bit scan can contain many, many more colors than its 24-bit counterpart. In practice, however, a 24-bit scan can contain more different colors than our eyes can even distinguish, so the difference is, for most projects, marginal and theoretical. In addition, 48-bit scans result in huge file sizes not only because of their greater data content, but because they can be saved as TIF files only, not as JPGs. As we learned on the Digital File Types and File Compression pages, JPG files use lossy compression that results in smaller, more manageable file sizes.

So, why offer 48-bit scanning at all? Here's why: Scanning slides in 48-bit is useful for high-end scanning projects from exceptionally detailed originals, such as from fine-grained transparency film, and to create files that will undergo considerable editing in digital photography software. It's nice to have because of the potential for more scanning "headroom", but in practice you'll do fine with 24-bit for most slide scanning projects.

Density range is the range of potential density from pure white to deepest black. Since all scanners can produce pure white, density range is given by the maximum density, DMax for short. High numbers are better: Measured on a logarithmic scale where 4.0 is the theoretical maximum. Many of today's film and flatbed scanners deliver DMax over 3.6. High DMax is important when scanning slides or negatives, to capture deep, rich shadows without losing detail.

Reflective media scanning. Usually a paper print, but can be any material of interest. Like a photocopier, but makes a digital file instead of a paper copy.

Transparent media scanning. Any transparent or translucent material, such as slides or negatives. This requires a light source that shines through the original. This is a given for dedicated slide scanners, and a feature of higher-end flatbed scanners. An absolute must for scanning slides and negatives!

Prescanning: A low resolution fast scan that displays the original, but does not create a digital file. Use prescanning to crop, make minor enhancements, choose a file name, file type, and destination.

Other options are specific to software, such as selecting Digital ICE to remove dust (see below) or sharpening ("unsharp mask" in some programs). Although I like Digital ICE, I never sharpen scans at this stage. All scanned files benefit from some tweaking in photo editing software, and sharpening is the last step of any editing process.

Scanner software

All scanners come with software that enables the scanner and computer to communicate.

In general, scanner settings are tailored to the individual item being scanned after prescanning and before the final scan is made. At its most basic, scanner software will allow:

Prescanning
Cropping
Resolution settings
Color vs. black and white setting

More versatile scanning programs feature more advanced controls, such as:

Selecting positive vs. negative film material (changes color output).
Brightness and contrast (either sliders, levels, or curves).
Saturation
Hue
Batch processing
Reflective vs. transparency scanning
A Photoshop plug-in, for direct importing into the PS workspace.
Digital ICE, a proprietary scanning feature that gets rid of dust specks on film material by adding an infra-red scan. Although it adds to scanning time, it virtually eliminates post-scanning dust speck removal. That works out to a big time-saver when scanning slides and negatives, and I recommend it highly!

Visit the Editing Digital Photos page for more about these common enhancements.

Even greater control is offered by third-party slide scanning programs such as Silverfast, but prepare for a steep learning curve.

Preparing slides and negatives for scanning: six scanning tips

Know your end-use, and choose scanner settings accordingly. Are you making archive copies of an original paper print? Scanning photos for the Web? Digitizing paper prints to email to a friend? Scanning negatives for a digital slideshow? Scanning slides for a long-term photo archive? Each use will have its own settings, and if you remember 100 dpi for screen display, and 300 dpi for prints, you're half-way there!

Clean your scanning surface with a lint-free cloth, and your original with lens tissue. Beware of fingerprints and other smudges!

Choose resolution wisely, in accordance with your end use. Consider scanning speed vs. image size/resolution. Higher scanning resolutions and Digital ICE take longer, but save time on the back end.

Scan to reduce post-processing. Take advantage of color controls at the prescan stage.

Save to 24-bit JPEG files (that's 8-bit color) with minimal compression. While it's true that JPEGs don't hold up to post-processing as well as TIFF or PNG files (and their much greater file sizes), consider this: scanning photographs is a controlled process, and there should be no need for major post-processing of scanned files. It's better to create a higher resolution JPEG than to save to one of the other file formats.

Your scanner can do more than just scanning slides, negatives and prints. It can also be used for some pretty cool close-up and macro photography. Learn to use your scanner as a camera, and let your imagination run wild!

Scanners as a teaching tool

There is a trend in photography education that incorporates scanning technology with traditional film photography. Students begin their training by shooting and hand-developing black and white film. Depending on available facilities, they may or may not then learn traditional printing in a black and white darkroom. They'll ultimately complete the cycle by scanning negatives to create digital files that are incorporated into a digital photography workflow.

I love this method of teaching photography! Photographers trained in silver-based photography are linked for life to a time-honored creative tradition. In addition, analog to digital conversion opens doors not available to the photography students of yesterday. Electronic imaging is where the action is, but traditional film photography can coexist, and enhance the power of digital photography.

In conclusion...

Scanning slides and negatives is a fantastic process that is giving new life to traditional film photographs. Flatbed scanners are versatile, affordable, and fun to use. There is also more to them than meets the eye: check out this page to see more!