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Dual Review
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Original Review Date: August 24, 1999 |
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Inexpensive "personal" film scanner |
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2438 dpi resolution (24.5 meg file from 35mm neg) | |
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8 bits per channel (Dmax not specified) | |
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High-speed SCSI interface | |
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Software accommodates beginners AND experts | |
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Optional APS adapter |
Overview
Minolta is a company with long experience in the world of film,
and extensive digital expertise that has so far been applied primarily
in the areas of office electronics and imaging (copiers &
printers). Recently though, they've been making significant waves
in the digital camera and scanner markets, with their highly capable
(and expandable!) Dimage EX 1500 Zoom digital camera, and a whole
line of film scanners covering everything from APS to 35mm, to
medium-format photography. We've previously reviewed the Dimage
Scan Dual (35mm and APS film formats), and the Dimage Scan Multi
(multi-format, from 8mm movie film to 6x9 cm medium-format). With
this review of the Dimage Scan Dual, the "personal"
model in Minolta's lineup, we complete our coverage of their scanner
lineup. (At least until they come up with yet another one!)
The Minolta Dimage Scan Dual film scanner is aimed at the "personal"
scanner market, and fits well within that market, with a very
affordable price, excellent resolution, and good control software.
With its APS adapter, it provides a good solution for scanning
that format as well, including the ability to "batch scan"
an entire roll without user intervention. - More on this later.
"High Points" Overview
The Basics
The Dimage Scan Dual is a desktop device about the size of a hefty
novel standing on edge. (The long side down.) It measures 3.6
x 6.3 x 10.7 inches (90.5 x 160.5 x 272 mm), and weighs about
4.4 pounds (2 kg). Interface to the host computer is via a high-speed
SCSI-2 interface, meaning you'll need to have such a port installed
in your computer to use it. (Macs typically come equipped with
SCSI connections: On a Windows machine, you'll need to have an
interface card installed. Appropriate cards range from $100 to
$300 in price. The manual lists a number of Adaptec SCSI cards
from the 1500 and 2900 series that are suitable. The only restriction
seems to be that the 1500-series boards don't work with NEC PC98xx
computers.) We've seen some resellers offering packages with a
SCSI card "bundled" with the unit, but more often have
seen just the scanner itself being offered. The standard unit
can scan 35mm negatives or slides, in either black and white or
color. An optional APS adapter is available for scanning that
film type.
The software CD shipped with the unit supports both Mac and Windows
platforms. A Photoshop acquire plug-in is provided for the Mac,
and TWAIN drivers for the PC, and Photoshop LE for both platforms
provides very full-functioned image editing capabilities: Big
kudos to Minolta for including such a powerful image-editing program
with their scanner! (NOTE: Minolta specifies that the scanner
requires either Windows '95 release 2 (OSR2), or Windows '98.
If you're running Windows '95, be sure to check the revision level
you have installed.)
Scanning resolution can be as high as 2438 dpi (apparently, a
2400-element CCD covering the width of a 35mm slide or negative,
with a few unused pixels on either side). This produces maximum
image sizes of 2336 x 3504 pixels for 35mm (24.5 megabytes), or
1776 x 2928 for APS (15.6 megabytes).
A note about scanner resolution, as compared to that of digital
cameras: The 8.1 megapixel resolution of the Dimage Scan Dual
is even higher than you might expect, when compared to the resolution
of a digital camera. Because the scanner's CCD samples each pixel
in all three red, green, and blue color channels, it's really
equivalent to a digital camera with a 24 megapixel sensor and
"striped" color filters. Thus, the first thing most
people notice about images scanned from negatives and slides is
the extraordinary level of detail captured. That said, the Dimage
Scan Dual's scan resolution of 2438 dpi is at the top of the field
for 35mm/APS "personal" scanners.
Another important scanning parameter is "bit depth,"
a measure of both color accuracy and the maximum density range
the scanner can recognize. (8 bits per channel is good, 10 better,
and 12 the best you'll commonly find in desktop scanners.) The
Dimage Scan Dual captures 8 bits per pixel, while its "big
brother" the Dimage Scan Speed captures 12. We found the
8-bit color depth sufficient for negatives and well-exposed slides,
but the Scan Dual did have trouble with our extremely dense "Train"
slide.
Scanner Optics & Light Path
Film scanners tend to take one of two approaches in their optical
design, providing either fixed or adjustable focus. The Dimage
Scan Dual employs fixed-focus optics. Given the extreme resolution
of most film scanners, we're surprised that the lenses can be
designed with enough depth of field to insure sharp focus in the
face of minor variations in the film plane position. We're surprised,
but the fixed-focus approach nonetheless seems to work quite well,
as evidenced by the performance of the Dimage Scan Dual. The upside
of fixed-focus designs of course, is that you don't have to worry
about focusing, either in the form of twiddling a thumbwheel,
or by waiting while the scanner adjusts its focus for every scan.
In our testing, the Dimage Scan Dual produced sharp images every
time, the sole exclusion being one orientation of our unusual
"USAF 1951" resolution target, which is a glass slide
with the pattern deposited on one side of it. With the pattern
facing one way, we got sharp results, but decidedly blurry ones
with it facing the other. We saw no evident focus deficiencies
while scanning normal slides or negatives.
The Dimage Scan Dual uses a special fluorescent light source,
producing strong spectral peaks in the red, green, and blue portions
of the spectrum. We observed that this diffuse illumination source
produced somewhat "softer" scans than some other scanners.
The resulting scans had less of a razors-edge on fine detail,
but were also much more forgiving of film defects and film grain.
A good analogy (for those old darkroom aficionados out there)
would be the difference between condenser and diffusion enlargers:
The condenser optics tend to produce sharper images, but at the
cost of greatly enhanced grain, while diffusion enlargers create
a softer look. Note in this though, that while the scans produced
by the Dimage Scan Dual have a somewhat "softer" appearance
to them, they in fact appear to carry an extremely high level
of detail, as evidenced by the results from our WG-18 (ISO-12233)
resolution target scans. Another characteristic of the Dimage
Scan Dual that impressed us was the complete absence of color
"aliasing", wherein closely-spaced, high-contrast detail
can cause flecks or streaks of color to appear that weren't in
the original image. Unlike some scanners, the Dimage Scan Dual
showed absolutely no tendency to produce artifacts of this
sort.
Film Handling
The Dimage Scan Dual uses plastic slide- and filmstrip-holders
to carry the film to the scanner: You first place the media to
be scanned into the holder, then insert the holder into the scanner.
The holders have detent notches on them that provide repeatable
film positioning, and yet allow for manual advance of the film
between frames. During scanning, the holder and film is moved
past a fixed CCD array. The filmstrip holder can accommodate strips
of 35mm film up to six frames in length, and the slide holder
up to four slides. Both holders are reversible, a necessary feature
for their use: Inserted into the scanner, you can access half
of the total film frames by sliding the adapter in or out. To
reach the remaining frames, you remove the adapter, flip it end
for end, and reinsert it.
We found both the slide and film holders to be quite effective
and easy to use. The film adapter is hinged, but only to the extent
that a plate flips up to expose the recess into which the film
is laid. (Unlike many "clamshell" designs, the slot
holding the film is a fixed structure.) The back pressure plate
then hinges back down and latches, clamping the film flat. This
arrangement did a particularly good job of handling curled or
damaged film, regardless of whether the film was curled side-to-side,
or along its length. The film-holding slot is about a half-millimeter
wider than the film itself, doing a good job of constraining the
film position, yet still allowing minor adjustments to be made
for fine alignment relative to the limits of the scanning area.
We did find that the filmstrip holder crops the 35mm frame very
slightly, about 3% in both vertical and horizontal directions
by our reckoning. (For some reason, this appears to be a common
characteristic of strip-film holders.)
The slide holder is also constructed of plastic, with four slots
along the top edge into which the slides may be loaded. The edges
of each slot set absolute limits for the horizontal position of
the slide mount, but there's a bit more play (about a full millimeter
side-to-side) with slides than is present in the filmstrip adapter.
This is probably a good thing, as it allows you to correct for
film misaligned in its mount: You can manually tweak the slides
to achieve about two degrees of rotation in either direction,
as needed. (Despite this looseness, we had no difficulty aligning
slides square to the holder, as the edges of the "windows"
in the holder provided good reference surfaces to align to, and
simply "bottoming out" the slide in the slot yielded
good alignment if the film was properly positioned in the slide
mount.) The slide holder is also a little unusual in the way that
the slides "float" between two sets of spring-loaded
fingers. This seemed to do a good job of keeping the film plane
well-centered about the point of optimum focus. The centering
fingers gripped a particularly thick plastic-and-glass slide mount
quite a bit more firmly than they did standard cardboard ones,
but handled a wide range of mounts well.
Our one quibble with the Dimage Scan Dual's film handling (and
a minor one at that) was that the slide holder didn't allow you
to insert the slide all the way into the carrier in a single step:
You had to push it in as far as possible from the top, then reach
in from the sides with your fingers to tug it all the way down
to it's final position. This left us a little nervous that we
might inadvertently smudge the film with our fingers, although
we never actually did so in practice.
Minolta shipped us the optional APS adapter along with the Dimage
Scan Dual, so we got a chance to try it out as well. (NOTE that
the APS adapter is an optional accessory, sold separately from
the scanner itself.) This worked quite well, although as with
other APS scanners we've used, there's what seems like an interminable
period of whirring and clicking (actually about 20 seconds or
so) before it begins an index scan: We assume this is necessary
to count the number of frames in the roll or something. The APS
adapter is a separate unit with a hatch on top that opens to reveal
an opening to receive the APS film cartridge. With the film inside,
the whole assembly is inserted into the front of the scanner.
The APS adapter contains a small motor that advances the film
between frames, and rewinds it into the cartridge when you're
done scanning. Once a desired frame has been positioned in the
opening on the side of the adapter, the 'Dual scans it by moving
the entire adapter in and out to move the film past the scan head.
The APS adapter seemed to work quite well, our only complaint
that being that it took a long time to produce an index scan of
the roll. (About 5 minutes for a 25-exposure roll!) As it turns
out though, this is really a non-issue, since you probably got
an index print with your roll of processed APS film anyway. Assuming
you know which frames you want to scan, it's an easy matter to
select the ones you want, prescan them, make whatever adjustments
you'd like for each, and then have the scanner batch-scan them
all, by control- or command-clicking to select those you're interested
in before pressing the "Scan" button.
System Interface and Included Software
As mentioned earlier, the Dimage Scan Dual uses a SCSI-2 connection
to the host computer, providing the high speed data transfer necessary
to handle the large amounts of data the scanner can generate.
No SCSI card is included with the unit, but Minolta lists several
models of Adaptec cards that the unit can be used with. Adaptec
is pretty much the standard for SCSI cards: You can find cheaper
ones, but the Adaptec models are more likely to be compatible
with a wide range of equipment. Note in particular, that some
scanners, CD-ROM drives, and other equipment ships with low-cost
SCSI cards included. In many cases, these are "dedicated"
cards, that will only run the particular device they're shipped
with. If you're buying a card to support the Dimage Scan Dual,
take our advice and get a "name brand" Adaptec unit.
The hassle you'll save will be more than worth it! (Also note
that there appear to be "bundles" available which include
a SCSI card along with the scanner: Check with your reseller to
see what's available.)
Once connected to the computer, the Dimage Scan Dual is controlled
through an excellent software interface that we'll describe in
greater detail below. As noted earlier, the scanner-control software
takes the form of standalone applications on both the Mac and
PC, as well as a Photoshop plug-in on the Mac, and a TWAIN component
on the PC. A particular strength of the Dimage software is the
extent to which it provides powerful controls for experienced
users, while at the same time offering a simple interface for
novices.
A nice touch in the Dimage Scan Dual package was the inclusion
of Adobe's Photoshop LE, for both Mac and Windows. Photoshop LE
is a slightly trimmed-down version of the full Photoshop package,
the primary omissions being support for color spaces other than
RGB (such as CMYK, for commercial offset printing), and less in
the way of color management. At one time, it was quite common
to find Photoshop LE or even a full version of Photoshop bundled
with many scanning devices. The combination of policy changes
at Adobe (implemented in the form of radically higher prices to
their bundling partners), and ever-tightening margins and declining
retail prices in the scanner market have all but eliminated Photoshop
from the "bundle" market. We applaud Minolta's inclusion
of this program with the Dimage Scan Dual though: We suspect that
many potential purchasers of the Scan Dual will be upgrading their
imaging capability with the acquisition, and won't already have
a copy of Photoshop. While trimmed-down somewhat from the capabilities
of the full version, Photoshop LE is a dramatic step up from the
"dumbed-down" interface and capabilities of Adobe's
PhotoDeluxe, a much more common software bundle component these
days. Don't get us wrong, PhotoDeluxe is an excellent program,
but is clearly targeted at the casual user. Even at that though,
we've long felt that removing key features such as the "levels"
control is no gift to the end-user. While it may make the program
easier to use, such simplification ultimately leaves users at
a dead end, with nowhere to go as their skills and abilities improve.
Photoshop LE is adequate to the needs of most semi-pro users,
and will provide the full range of capabilities that most users
will need to achieve the best results. Flame off for now, but
repeated kudos to Minolta for taking the cost hit and including
Photoshop LE with the scanner. One parting shot: You can't buy
Photoshop LE, only the full version of Photoshop, which routinely
sells for well over $500. Given that the LE version will be enough
for the majority of users, the argument could be made that its
inclusion in the Dimage Scan Dual bundle will save many people
$500 or more. This fact alone is a significant differentiator
for the Minolta's product.
Speeds and Feeds
As its name suggests, the Dimage Scan Dual is intended to be a
fast scanner. In our testing, we found that it did indeed zip
along pretty quickly. This appeared to be due partly to the basic
mechanism and electronics (which moves the film and digests the
data rapidly), and partly to the fixed-focus optics: When you
tell the unit to begin scanning, there's no delay for focus adjustment
before the scan starts. The unit does make one pass over the negative
or slide first though, to determine an autoexposure level, a process
that takes 4-5 seconds. Scanning throughput was quite good with
the unit, helped by the flexible, easy-to-use software, but also
by the fast scan times themselves. (We've only recently begun
meauring preview and scan times, so won't have comparable numbers
for many scanners we've previously tested. From this point on
though, we'll be measuring these throughput-related timings on
a routine basis...) Running the Dimage Scan Dual from our 333
MHz PowerMac G3, we measured the following scan times:
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Preview w/o autoexposure: |
15 seconds |
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Preview w/autoexposure: |
25 seconds |
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Low res (~600dpi) full-frame scan w/o autoexposure: |
35 seconds |
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Low res (~600dpi) full-frame scan w/autoexposure: |
72 seconds |
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Full res (2438 dpi) full-frame scan w/o autoexposure: |
86 seconds |
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Full res (2438 dpi) full-frame scan w/autoexposure: |
133 seconds |
Operation and User Interface
Other than the actual scans themselves, most of the story to be
told about a film scanner has to do with the software that drives
it, and to what extent the combination of hardware and software
makes it easy to produce good-quality scans. Accordingly, we'll
devote a sizable of this review to talking about the software
that drives Minolta's Dimage family of scanners, and the Dimage
Scan Dual in particular.
As noted several times already, we feel that Minolta has done
a particularly good job of balancing capability with ease-of-use.
This is a difficult equation to optimize, as the needs of "beginners"
and "experts" can vary so widely. At the same time,
the goal should be to provide a smooth gradation of capability,
not introducing any abrupt hurdles to overcome as the users advance
in their sophistication. Minolta has accomplished this difficult
design goal by providing very basic, visually-oriented contrast/brightness
adjustments for neophytes, while at the same time offering fairly
sophisticated histogram and tone curve controls for those comfortable
with more complex adjustments, and who need the control they provide.
As we write this, we're still searching for our "formula"
that works best for scanner reviews, but are generally settling
on a format in which we step through the scanner controls in the
approximate order that a user would encounter them. (For a more
complete walk-through of scanner operation, check out Minolta's
excellent web site for their scanners: They've put together a
comprehensive "on-line demo" of how the software works.)
The Control Window(s)
The most basic options and functions of the Dimage Scan Dual scanner
are controlled via the Control window, shown below in its two
versions. This window represents a merging of two windows on the
earlier version of Minolta's scanning software, and greatly improves
ease of use in our opinion. We liked many aspects of Minolta's
scanning software in the past, but did find the concept of "Jobs"
in the scanning setup rather confusing. For whatever reason, most
scanner software seems to overly complicate the relationship between
input and output resolution and file size. The two versions of
the "Control" window take different approaches to handling
this relationship, but both are simpler than most we've encountered,
and are a significant improvement over earlier versions of Minolta's
software.
Standard Control Window
The Dimage Scan software provides simplified scan-size options
when operating in "Standard" mode. (See the Preferences
screen described below.) In this mode, for the most part, you
don't need to worry about pixels per inch, dots per inch, etc.
You just tell the program what sort of output you're interested
in (Screen, Pasted into a word processing document, or Printed
or modified with PhotoDeluxe), and how much of the page you intend
for the image to occupy, and the software figures out the pixels,
magnification, etc. for you. Here are the controls available on
the Standard Control Window. Note that the controls labeled "APS
Only" do not appear in this window if 35mm is selected as
the film type: (NOTE: This and all screen shots following have
been scaled-down to better fit the 'web page -- The actual screens
are larger and more readable!)
Preferences
Button - Brings up the Preferences window, described later.
Index
Button (APS Only) - Brings up the Preferences window,
described later.
Save
Index Scan Button (APS Only) - Brings up the Preferences
window, described later.
Prescan
Button - Brings up the Preferences window, described later.
Scan
Button - Brings up the Preferences window, described later.
Batch
Scan Button - Brings up the Preferences window, described
later.
Help
- (If you need us to explain what this button does, you probably
shouldn't buy the scanner! ;-)
Rewind
Button (APS Only) - Rewinds APS film back into its
canister.
Precision Control Window
This version of the control window provides much greater control
over input size, output size, and resolution. Here, you can specify
any element of the scanning resolution or image size, and the
other parameters will follow in lockstep where appropriate. In
the screen shot below, we've specified that we want to work in
pixels, rather than inches or other linear measurements, so the
Output resolution and Input Size windows are disabled. If you
select inches, cm, or other measure in the "Unit" window,
you'll have full control over all entry boxes. Many of the controls
in this window are the same as in the Standard Control Window,
so we won't repeat their descriptions here.
Save/Load
Settings Buttons - To save time on subsequent scans (as well
as provide a useful index of images on your APS rolls), you can
save APS index scans to disk.
Preferences Dialog Box
The preferences window (not shown) controls
a number of overall settings governing scanner operation. You'll
probably need to visit this screen only infrequently, to set up
the defaults for how you want the software to work. (For instance,
whether to use the Standard or Precision Control Windows). Herewith
the Preferences functions:
Prescan Window
This window (shown below) is "home base" for the scanning
process. From here, you'll launch off into other functions within
the software, to adjust color balance, contrast, or tonal range.
Controls here also adjust preview orientation, data readout, and
exposure parameters for sequential scans. See the text following
the screen shot for a description of the individual buttons and
controls.
Here are the Prescan Window controls, reading from left to right
and top to bottom, for all the buttons along the bottom edge of
the screen:
Orientation and Viewing Controls
(Grouped in the lower left-hand corner)
Rotate
Right Button - Rotates preview (and final scan) 90 degrees to
the right. (Clockwise)
Rotate
Left Button - Rotates preview (and final scan) 90 degrees to
the left. (Counterclockwise)
Flip
Horizontal Button - Flips picture horizontally.
Flip
Vertical Button - Flips picture vertically. (The two "flip"
buttons find frequent use when flipping the slide or film carrier
to scan frames at both ends.)
Zoom
In Button - Zooms in on a selected area of the pre-scan window.
Zoom
Out Button - Zooms in on a selected area of the pre-scan window.
"Grabber"
Button - This button turns the cursor into a "grabber",
that lets you drag the pre-scan image and drag it around, to
see various areas when the pre-scan image has been enlarged with
the Zoom Button.
APS
Format Button (APS Only) - Lets you select between the 3 standard
cropping dimensions for APS film, Conventional, HDTV, or Panorama,
as well as fully-manual cropping as in 35mm mode.
Image Adjustment Controls
(Grouped in the lower right-hand corner. Most take you to secondary
screens shown below, where you can modify the tone and color balance
of the scanned image.)
Variations
Button - This leads to a screen (described in more detail below),
where you can quickly adjust brightness and contrast, by the
simple process of repeatedly choosing the most appealing of 8
alternate versions of the image. - An excellent tool for novices
to quickly adjust their images.
Tone
Curves Button - Probably at the opposite end of the ease/power
spectrum from the "variations" control, the tone curves
screen (described in more detail later) provides the powerful
ability to edit the tone curves for both the image as a whole,
as well as the individual red, green, and blue channels.
Histogram
Button - This is our favorite scanning/image adjustment tool!
(Also described in more detail later.) To our mind, histogram-based
image adjustment offers the best tradeoff between ease of use
and power for most mid-level users.
Full-Screen
View Button - Enlarges the currently-selected region of the pre-scan
window to full-screen size. (Note though, that this enlargement
is only a pixel replication, so it becomes rather pixellated
when smaller regions are magnified.)
Reset
All Button - This button resets all the image adjustments to
their default settings, letting you quickly back out of a set
of adjustments and return to "zero."
Readouts/Information Displays
At the bottom left-hand corner of the Prescan window, there are
two sets of readouts, one showing the dimensions of the current
cropping frame, in mm, and the other the RGB (or CMY) values of
the point under the cursor in the preview window.
Variations Adjustments
It's often difficult for novices to decide what to do to an image
to make it look better. More contrast? Less brightness? A little
of both? Frequently, after playing with an image for a few minutes,
you end up with something that looks worse than when you started!
Yet, even the rankest amateur can generally tell whether picture
"A" looks better than picture "B". Taking
advantage of this, Minolta offers a "Variations" tool,
as shown in the screen shot below. Here, the current contents
of your cropping frame are displayed in the center of a matrix
of images, with those around the edges of it representing the
effects of more or less contrast or brightness. (Contrast variations
run vertically, brightness variations horizontally.) If you decide
you like one of the variations presented more than the current
image, just click on it: It becomes the new reference sample,
and the variations adjust to reflect changes relative to the new
center image. By continuing to click on the image that you like
best, you can quickly home in on the optimum brightness/contrast
setting.
After you've set the contrast and brightness, you can then
correct the overall color balance of the image, by adjusting the
R, G, and B slider controls at upper left. Always wait to adjust
the color until after you've made the brightness & contrast
changes though, as you'll frequently find that perceived color
problems diminish once the brightness and contrast are properly
set.
The "Variations" screen also has a button that enlarges
the current selection to full-screen size, making it easier to
assess the current picture quality. We felt that this feature
was marred slightly though, by the fact that the enlarged image
is only a pixel-replicated copy of the original area, which can
lead to rather pixelated images if your cropping frame is small
relative to the overall film area.
Histogram Adjustments
As we noted earlier, Histogram adjustments are by far our preferred
method for quickly correcting tone and color problems in digital
images! For those not familiar with histograms though, a brief
explanation would probably be in order.
A histogram is simply a graph of how many pixels in an image have
each possible brightness value. A large peak on a histogram graph
means there's a lot of pixels (a large area) with roughly the
same brightness values. Likewise, if the histogram curve is near
zero, it means relatively few pixels have those brightness values.
To understand how this helps image adjustment, we've included
a couple of sample images below, showing two images set up with
different brightness and contrast settings, and the histograms
associated with each.
 Dull, flat image has a compressed histogram, with no information above the midtone level in any channel. |
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In the first sample, we have a rather low-contrast, dark image. Low contrast means that there's not a great deal of difference in the brightness values between the brightest and darkest pixels. "Dark" means that the bulk of the pixels in the image have fairly low brightness values. In the histogram curves for this image, note how the right-hand side of the curves (high brightness values) are flat, because there aren't any pixels with those brightness values. Also, note how the histogram curves occupy a fairly small amount of the horizontal space allotted to them.
 Well-balanced image shows full range of tonal values in histogram, in all channels. |
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By contrast (no pun intended!), observe the image above: Contrast
and brightness are about right, and the results are readily evident
in the histogram curves for it. Notice how the curves occupy much
more of the available horizontal space, meaning that pixel values
are spread much more evenly across the available tonal range.
Notice too, how you can even tell about color balance from histogram
displays. Notice the large "hump" near the middle of
each curve? What object in the image do you suppose this large
group of pixel values corresponds to? (It's the background.) Now,
if we want the background to be a neutral gray, what do you suppose
the display would look like. (The peaks in red, green, and blue
would all line up with each other, meaning that the average R,
G, and B values would be about the same.) Can you guess how the
color balance needs to be adjusted to achieve this?
Notice the sliders under the individual histogram curves. These
are used to set the brightness values the scanner will consider
to be the minimum (black), maximum (white), and a middle value
(gray), for each of the color channels. If you move the "black"
slider up from the leftmost position, you're telling the scanner
to treat that value as "zero" for the color channel
involved. Any values darker than that will also be treated as
zero, and values brighter than it will be proportionately stretched
downward so that the brightness values will extend smoothly down
to zero. Likewise, the "white" slider on the right sets
the value that will be considered as a maximum, and mapped to
a digital value of 255. Anything brighter will also be set to
255, and darker values will be "stretched" smoothly.
The middle slider sets the value that the scanner will put in
the middle of the brightness scale (the "50%" point).
Anything brighter than the level set by the slider will be made
brighter than 50%, anything darker will be made darker. Thus,
to lighten the image overall, you'd move this slider to the left,
so that more of the brightness values would be pushed above the
50% point. (This all sounds more complicated than it is: You'll
figure out what the sliders do after just a couple of minutes
of playing around.)
The histogram screen includes "before" and "after"
previews, and a number of controls for adjusting the image. At
middle left are three of the most immediately useful tools, the
eyedroppers for setting white, black, and gray points. If you
select the black eyedropper button, and then click on a point
in the left-hand preview window, that point will be set as the
"black" point, and the individual red, green, and blue
black-point sliders will all adjust automatically to make it so.
Likewise, selecting the white eyedropper button and clicking in
the left-hand preview window will set that point as the "white"
point, moving the red, green, and blue white-point sliders as
needed. (Anyone want to guess what the gray eyedropper button
does?) In practice, you'll find that the eyedropper controls offer
a very quick way to color-balance many problem images in a matter
of seconds.
Part of the beauty of the Dimage Scan's histogram screen is
the way it shows histograms for all three color channels separately,
yet also allows you to operate on all the channels at the same
time, if you wish. By default, you can adjust any of the slider
controls independently of any other. What if you want to make
an overall adjustment to the image as a whole, though? In the
lower left-hand corner, the button with the three colored bands
on it is the "RGB synchro button." Clicking this button
locks the sliders for the red, green, and blue histograms together,
so that moving any one of them moves the sliders for the other
two colors the same amount.
The other control buttons in the lower left-hand corner let you
see the effects of your adjustments on the histogram, as well
as save and retrieve complete sets of adjustments once created.
This last ability is a particularly welcome one, as many lower-end
scanners don't permit you to save adjustments for later use. Often,
we find ourselves wanting to save a group of settings before engaging
in further experimentation, so we have a known good point to return
to if our twiddling goes awry. Also, you may have a group of photos
shot under similar conditions that would all benefit from the
same treatment.
One odd point about saved and subsequently recalled histogram
corrections though: When the Dimage Scan software applies a previously
saved correction to an image, it does so on top of whatever
correction may currently be in effect. Thus, the effects of recalled
corrections are cumulative with any you've already applied. If
you want to return to a prior state, you'll need to reset all
corrections (using the Reset button) before applying the saved
settings. (This isn't any sort of a problem, but was different
than how we expected the saved settings to work. We're passing
the information along here to hopefully save our readers a few
minutes of puzzlement when they encounter the behavior for the
first time.)
A full treatment of histogram-based tonal adjustments is far beyond
the scope of this review, but we encourage users to spend some
time playing with the controls on this screen: They're simple
to master, but quite powerful to use.
Tone Curve Adjustments
The tone curves window (shown below) offers a set of controls
that are at once easier to understand than those of the histogram
display, yet considerably less straightforward to apply effectively.
Even here though, minor tweaks by Minolta contribute greatly to
ease-of-use.
In concept, tone curve controls are as simple as can be: They're
nothing more than a graph of output brightness values against
input brightness values. Essentially, they say "whenever
you see brightness 'x', replace it with brightness 'y'. The input
brightness values (those of your original image) are arranged
along the horizontal axis of the graph, and the output values
(those your image will come to assume) are arranged along the
vertical axis. Again, the easiest way to understand how a tone
curve works is to play with one. A little experimenting will reveal
that a steeply sloping curve produces high contrast, while a flatter
one produces less. Likewise, a curve bulging upward results in
a brighter image overall, and one drooping downward makes for
a darker one. The Dimage Scan software lets you adjust either
the overall RGB curve, or each of the color channels (red, green,
and blue) individually.
Tone curve controls let you adjust parts of the tonal scale,
without affecting others. As such, they're more powerful than
the histogram controls, but you have less feedback as to what
parts of the image you're affecting, and it's much easier to get
lost in your adjustments with them. Experienced graphics professionals
rely on tone-curve adjustments almost exclusively though, because
they provide such a high degree of control over the tone and color
balance of images.
The tone curve controls in the Dimage Scan software work like
those of most any high-end image editing program: You can click
any point on the curve and drag it, and the rest of the curve
will bend smoothly to pass through the point you've defined. You
can set multiple control points by clicking on more than one part
of the curve. You also have the ability to draw your own curve,
using a pencil tool, allowing you to create abrupt discontinuities
if desired. Minolta added a unique twist to the tone curves though,
in the form of white and black-point eyedropper controls, which
work in the same way as the equivalent controls on the histogram
screen. While a seemingly minor point, the eyedroppers can quickly
make gross adjustments in the overall tone and color balance,
and provide a good jumping-off point for your own finer adjustments.
Test Results
As always with Imaging Resource reviews, we encourage you to let
your own eyes be the final judge: Look at the sample images, download
them, print them out on your own printer, and decide for yourself
how well the Dimage Scan Dual would meet your requirements!
Overall, the Dimage Scan Dual turned in a good performance, competing
well in the "personal" scanner catetory with other units
in its price range. Particularly when compared to the digital
cameras that constitute the other major review focus of this site,
readers are bound to be impressed with the incredible amounts
of detail a scanner like the Dimage Scan Dual can extract from
a slide or negative.
We found that the Dimage Scan Dual produced good scans with the
default settings, and that the software controls available made
for easy modification of the images. On the Mac, the default settings
tended to produce slide scans that were slightly dark with our
screen gamma set to the "standard" value of 1.8 - Actually,
the scans were a little light when no explicit gamma settting
was made. A minor bump of the midtone point using the histogram
control quickly brought the overall tone into a reasonable range
though.
By comparison, scans of color negatives were a bit light, but
a minor drop of the midtone point tended to quickly compensate.
Color balance overall was quite good, although by default, the
scanner tended to add a bit of magenta to things (red and blue
together). We suspect this might be an attempt to compensate for
typical computer monitors, which tend to have a very bluish white-point,
frequently as high as 9300K. Again, it wasn't too difficult to
compensate for this tendency, and the ability to save and recall
sets of tone and color corrections was a valuable feature. Overall
color accuracy was excellent, with color saturation just a notch
away from the very best we've seen to date (January, 1999). (Like
the Dimage Scan Speed though, color saturation in greens on transparency
(slide) scans is a bit weak.)
Resolution of the Dimage Scan Dual was excellent, but hard to
"call" based on our standard test targets. The reason
for this is that an unusually low level of "aliasing"
had us convinced we could easily see discernible detail in the
WG-18 target all the way out to 1400 lines per picture height
in both horizontal and vertical directions. This doesn't make
sense, given that there are only 2600 pixels vertically in the
resolution-target image, meaning we really "shouldn't"
be able to see anything beyond about 1150 line pairs/picture height.
Nonetheless, the scanner clearly resolves at least some detail
all the way out to 1400 l/ph. (Note that the slight cropping the
scanner did to the 35mm frame wouldn't be nearly enough to produce
the increase in apparent resolution we observed.)
The USAF resolution target gave (as usual) more conservative resolution
figures, with the scanner resolving cleanly down to 28.5 line
pairs/mm, (724 line pairs/inch), and with some aliasing, down
to 45.3 lp/mm (1151 line pairs/inch). With natural subjects, the
scanner's fluorescent light source produced a somewhat softer,
less grainy look than some other units we've tested, although
there seemed to be no loss of detail information in the scans
associated with this softer "look".
See for Yourself!
Take a look at the test images
from the Dimage Scan Dual, download them, print them out, and
see if this scanner meets your needs!
Conclusion
In the Dimage Scan Dual, Minolta has crafted a combination of
capabilities and software features into a unit that produces good
image quality with a minimum of tweaking. Even better, when it
does come time to manipulate color and tone, the software controls
provide a full range of capabilities, satisfying users ranging
from rank amateur to experienced
Reader Comments!
See what other
Imaging Resource readers have had to say about the Dimage Scan Dual,
or add comments of your own. (Do you have a Dimage Scan Dual? Share your experience!)
Read what's here, then add your own!
Visit the Minolta
web page for the Dimage Scan DualView the Minolta
"How2Scan" On-Line Demo Web Site
