While this
may be purely of academic interest, I thought it would be a good idea to
demystify scanner mechanics a bit. Think of a scanner as a potentially high
megapixel imaging device that converts image information from film or prints to
a digital file. Just as in a digital camera, the image can be manipulated
during the conversion process and given certain attributes, such as correction
of color and enhancement through contrast and saturation choices.
For those
who have not worked with a digital camera a scanner is akin to a copier. But
the scanner does not have toner or nozzles to lay down the copied information;
it creates digital image information that can be manipulated to mimic the
copied image or to enhance or adjust as needed.
This Epson 850V scanner scans both prints and film using a flatbed design. This illustration shows slides in the film holder, which is then placed directly on top of the platen.
In essence,
a scanner contains an RGB sensor, just as in a digital camera that, in
flatbeds, sits underneath a glass covering onto which the material is placed.
Flatbed scanners have both fixed and movable mirrors and a movable light source.
The movable mirror and light scan across the surface of the image and direct
the results through a lens to the fixed mirror, which directs it to the RGB
sensor. In essence, it “writes” the information as it goes. Depending on the
quality of the scanner, the light source in a flatbed can be LEDs or some
variety of a tube of light.
Film
scanners differ slightly in how the image is captured. Strips of film or
mounted slides are put into a holder that is then inserted into a slot in the
scanner. In a flatbed the film is placed onto the glass platen within holders. When
an image is selected for scanning in a dedicated scanner a stepper motor moves
the frame across a lens that directs the image to the sensor.
Here's a Plustek dedicated 6x6cm film scanner. Frames and strips are placed into a holder that is then inserted into the film gate, which then "steps" the image across the scanning module.
While the
mechanics of a scanner are fairly straightforward, the software and
capabilities of the sensor can vary considerably, depending on price and
manufacturer. In the next posting I will offer some criteria that should be
used to choose a particular scanner for the work you have in your collections.
Scanner specs are important to understand as they will determine what you can
and cannot accomplish in your work.
Every
scanner works in basically the same fashion and there are a number of steps
required prior to making the final scan. The first is a preview, a sort of
large thumbnail (not full resolution) image, often called a “prescan.” While it
serves as a rough guide to the image it should not be taken as what you could
or should expect from the final scan, just as the image review on your digital
camera’s LCD is certainly not what you will achieve after image processing
later.
Once you
have the prescan on the screen you can make various adjustments. The heart of
the scanning process is the software through which you process the image. This involves
choosing the resolution, the bit depth, noise reduction, dirt and scratch
elimination, dynamic range, color balance and more. These choices will be
examined in detail in the scanner workflow postings of this project.
Here's a screen grab of Epson's scanner software with many of the control modules opened. Image controls in software can be basic or quite sophisticated, but most allow you to make the kind of adjustments you need to create a good quality image file from the film or print you are scanning.
The changes
you make to the prescan is where you set up the parameters of the scanned image,
much as you set up the image-processor in a camera to deliver a certain look and
resolution of a captured image. Scanning software can be quite sophisticated,
and learning about its many options is key to creating quality image files from
the original material.
By
understanding what a scanner can deliver, and what program to utilize to get
the best possible results, you will be well on the way to making the right buying
decision and accomplishing your goal of archiving your precious film and print
images.
Next
posting: Scanner Specs
