Sigma SD14 Resolution: 14 MP? 4.6 MP?
Background
It's not often that I get excited enough about a new camera to
take a look at some technical aspect of the camera, but whenever there is a
fundamental change that could affect the future of digital photography, I like
to discover just what the impact is and how it could affect future products.
Being the owner of Digital Domain Inc. and the author of
Qimage and
Profile
Prism, I don't have the time to do in depth camera reviews, take sample
photographs, critique the camera body and controls, and so forth. What I
can do is delve into the heart of what makes a new camera stand out from the
pack. Since Sigma introduced the SD9 as the first prosumer full color
capture camera, I've been hoping that the full color capture technology would take
hold and we'd soon see the end of cameras using single color capture (Bayer
mosaic) sensors. The RGBG sensors used in nearly all dSLR's today can only
capture one of three primary colors at each pixel: red, green, or blue.
The Foveon sensor used in the Sigma SD9/SD10 of yesteryear and the newly released
SD14 can capture all three primary colors at each pixel site on the sensor.
While all other consumer/prosumer dSLR's capture only 1/3 of the
color information for each pixel when compared to the SD14, what does this
really mean as far as image quality? Is the SD14 really comparable to 14
megapixel cameras? How could it be when the SD14 produces a 4.6 megapixel
final image? Sigma markets the SD14 as a 14 "megapixel" camera because it
records 14 million pieces of information for each image. By comparison, a
standard 14 MP dSLR also records 14 million pieces of information but it spreads
the color information thin in order to gain resolution. Few people can in
their own mind equate this to overall image quality to know what effect "full
color capture" has on actual photos.
The "Bayer Blur "
Having spent years developing color interpolation algorithms
that try to take one color per pixel and reconstruct the missing 2/3 of the
information, I can tell you I have never been a big fan of the Bayer RGBG sensor
design. In my opinion, it's simply a bad idea that has been implemented
with enough finesse to make it quite effective given the obvious limitations.
It's similar to the internal combustion engine which is also a very dated and
relatively simple
design that has been refined to the point that it actually works quite well.
Capturing one color per
pixel has inherent problems such as the fact that an antialiasing (basically
blurring) filter must be used to spread light over a larger (than one pixel)
area because at any pixel on the sensor, it takes a minimum of 9 pixels to
capture all three primary colors! The fact that so many (adjacent) pixels
are needed in order to estimate the color of any given pixel in the final image also means
that edge detail and sharpness can suffer significantly when shooting subjects
that only stimulate one or two of the primary colors. A deep red or blue
subject suffers the most since the red and blue sensors only account for 1/4 of
the pixels on the sensor. A red rose, for example, may be noticeably less
sharp and the veins in the petals may be far less detailed on a standard dSLR
because only the red pixels on the sensor are gathering any useful data.
At that point, your 12.7 megapixel Canon 5D has just turned into a 3.2 MP
camera. Fortunately, there are very few subjects that are the exact shade
of red needed to only stimulate the red pixels on the sensor. Even a red
rose will likely excite the green and/or blue sensors to some extent and even a
little bit helps as that information (in the blue/green sensors) can still be
used to resolve detail. Still, with the standard Bayer one-color-per-pixel
design, resolving power will drop off at least to
some degree whenever you are shooting a subject that is not black and white.
Both theoretically and in practice, a standard camera's resolving power will begin to drop whenever a
non-neutral color appears in the frame.
A brief look at the SD1
The SD14 is the newest entry using Foveon's full color capture sensor design in a
Sigma camera. Full color capture means that all three colors (red, green,
and blue) are captured at each
pixel location on the sensor. Capturing full color eliminates the need for
the "Bayer Blur", antialiasing, and the "finagling" of color around edges that
can make some areas look unsharp on a standard camera. While the SD9/SD10
used similar technology, those cameras were more limiting in that they had no
in-camera JPEG shooting mode, a necessity for some journalistic type work, and color was often a bit inconsistent under
different lighting necessitating more color tweaking than would normally be
necessary. Still, the 3D effect or "presence" of images from the SD9/SD10
was unrivaled. Until now! The SD14 has improvements in color
accuracy, noise, and resolution that make it a solid contender that can compete
with the best dSLR's on the market today.
To be honest, I never quite got the hang of my Canon 5D. It
often underexposed even under relatively controlled conditions where my previous
300D, 10D, and 20D never had a problem, and I never quite got used to the full
frame light falloff that can darken the corners of some shots near the wide end
of the zoom range. Worse, I just could never get a shot from the 5D that I
felt lived up to my expectations as far as sharpness and detail. This
could be more a result of my lack of photographic skills than anything else
since I don't proclaim to be a professional photographer, but it's odd that I
never had trouble with my older 10D or 300D just as examples. To be honest, many of
my 5D photos actually look gorgeous printed up to 13x20 and even beyond, but
being on the software and engineering side of things, I'm a pixel peeper and I
often expect to see excellent detail when viewing the image on screen at 1:1
(100% zoom) and it just wasn't there. Sure, the 5D has so many pixels that
the amount of detail at 1:1 viewing on screen is of little consequence when
printing, but it
just might be a hint that all those extra pixels aren't quite adding up to what
they should mathematically and that's why I'm so excited about what I'm seeing
from the SD14 so far.
While
I haven't taken enough shots with the SD14 to know if the
color consistency problems that I had with the SD10 have been solved
and if the
camera does exactly what I need it to, it sure is producing shots that
I'm
personally much happier with right out of the box than the 5D has been
able to
give me in over a year working with it! Again, I'm not trying to
"put down" the 5D
because we all know that a photographer must pick his/her tools and
without a doubt
the 5D would be a better fit than the SD14 for others who are reading
this,
particularly if you happen to have a large investment in Canon
lenses.
For me, just after taking my first few dozen shots, I'm getting photos
from the
SD14 that are simply in a different league from (better than) what I
was getting
from the 5D. Is that just me? Am I just too lame to use the
5D
properly. ;-) Maybe. Time will tell once the more
photographically inclined reviewers start doing their real reviews of
the SD14.
For now, I'm beyond impressed with the SD14 and the few issues I've
found with
its operation appear minor and should be fixable with firmware
updates! There is a bug in the v1.00 firmware that causes the
"color space" selection of Adobe RGB to not stick as it should and the
setting
reverts to sRGB once the camera is powered down and back up.
Actually, it
only partly reverts because some indicators show Adobe RGB while others
show sRGB so
you really don't know what to think if you want to set the color space
to Adobe
RGB and keep it there. If you have firmware v1.00, I'd suggest
choosing
sRGB in the menu and leaving it there, as there appear to be multiple
bugs
related to choosing Adobe RGB. I'm sure a firmware fix could
easily address that
problem and it only affects JPEG shooting and not raw anyway which is
where I
spend most of my time. The jury is still out on battery life
since after
fully charging the battery, I only got about 15 shots before the
battery
indicator was at the half depleted mark on the display. From what
I
understand from others, the indicator seems to drop to halfway sooner
than it
should and I have shot another 30 or so shots since then with the
indicator
still sitting on the halfway mark so the indicator itself may be a bit
liberal
in its estimation of usage. One little oddity popped up when
playing back
images on the LCD in that I got some strange flashing/banding on the
display.
A power off/on fixed it and it was an LCD display issue only as the
images were
fine. It'll be interesting to see if that little glitch will pop
up again.
Other than these few things making me feel that firmware v1.00 might be
a little
glitchy, when you see the photos that this camera takes, the little
things just
don't matter any more!
Hit me with your first shot
After charging the battery, the first thing I did was to pop up
the flash and fire off a shot. At this point, my intent was to do nothing
more than make sure the camera was working, that I could download and process the
files, etc. I turned 90 degrees to my left where Jake was sitting in the
window and fired off this shot which shot in raw (because
that's the camera's default) and I developed as-is with no tweaks/changes.
This was my first shot from the camera, and the WOW factor had already hit me
like a freight train! With this first shot, I had already gone beyond the
level of sharpness and detail I thought possible with a camera. I had been
struggling for so long to get a shot with decent detail and sharpness with the
5D and I take one with the SD14 that blows me away just by "accident". From there,
things just got better and better! Since I've always had to "fight" my 5D
to get the proper exposure without tweaking the photos after the fact, I thought
maybe my first shot was just a fluke. My second shot,
however, had perfect exposure too, as have all 40-50 shots so far!
Resolution/detail: comparing the SD14 with the big boys
I have revised the resolution shots
to include six primary colors (red, green, blue, yellow, magenta, and cyan).
Red seems to be the worst case scenario for Bayer sensors so I wanted to get a
more balanced measurement using various colors. As a result, much of this
page from here forward has been revised.
Added 03/21/07: Added 20D resolution tests.
My
findings with respect to the SD14's resolving power are about what I
expected. Visually, the detail and 3D presence of SD14 photos are
amazing,
but I wanted to see if I could quantify this a bit. I already
knew that as
far as resolving power, the 5D would have the edge for black and white
detail
like that of a resolution chart, but what about the details in colorful
subjects? Would things start to fall apart when photographing
subjects
close to primary colors like red or blue? Instead of looking at
horizontal
and vertical lines on a typical resolution chart, I chose to use star
sector charts as they should be better suited for identifying the point
at which both the 5D and SD14 are no
longer able to resolve detail reliably. The charts below all
start at 500 LPI (lines per inch) at the outer most point where the
lines are the thickest.
By measuring the distance from the outer edge to the point at which the
lines
start to blur together, we can calculate maximum resolution.
While I
confirmed that, as expected, the SD14 was able to resolve the same
amount of
detail regardless of color, Bayer cameras like the 5D will have more or
less
resolving power depending on the color being sampled.
Here are the resolution crops just as they came out of the cameras with no
resizing or tweaks other than a click on white to fine tune white balance. If you are wondering about
the reds, the SD14 appeared a bit weak on the reds while the 5D had a little too
much punch in the reds. The actual red was somewhere between the two. Neither camera was perfect with
respect to color accuracy under my mixed lighting but it was of little consequence for
this test. Images from the 5D are labeled "C" for "Canon" and images from
the SD14 are marked "S" for Sigma. Here, the SD14 images will obviously
appear smaller because the SD14 produced final photos that are about 4.6 megapixels compared to the 5D's 12.7 megapixels.
Notes on the setup:
- Canon 5D using 24-70 f/2.8 L lens at mid zoom
- Sigma SD14 using 18-50 f/2.8 lens at mid zoom
- Both cameras set to f/5.6 aperture
- Resolution chart framed the same way and covering the same area of the
image in both cameras
- Both cameras shot raw: processed in SPP 3.0 (SD14) and
Bibble 4.9* (5D)
- In-camera JPEG's produced nearly identical results (not shown) for both
cameras
* Also tried Canon's DPP 2.0 for 5D and several other converters but Bibble
produced the best resolution.
Canon EOS 5D |
Canon EOS 5D |
Canon 20D |
Canon 20D |
Sigma SD14 |
Sigma SD14 |
|
|
|
|
|
|
Measured Resolution
|
Canon EOS 5D |
Canon 20D |
Sigma SD14 |
B/W |
2100 |
1700 |
1700 |
Red |
1630 |
1400 |
1700 |
Green |
2000 |
1680 |
1700 |
Blue |
1750 |
1480 |
1700 |
Yellow |
1950 |
1600 |
1700 |
Magenta |
1800 |
1500 |
1700 |
Cyan |
2000 |
1700 |
1700 |
Average |
1890 |
1580 |
1700 |
The resolution values listed above represent the point at which the lines
begin to blur/distort at any point around the arc of the circle. Imagine
placing the pin of a protractor at the center of the chart and drawing
concentric circles with the pencil starting at the outside edge of the chart and
moving in. As you move in, the first point where your pencil-circle meets
any lines in the graph that are blurred/smudged together, stop and the
resolution can be measured at that point. Of course, since these are
photos, we do this by using a photo editor and drawing circles digitally to see
where the blurring/smudging starts. Since there are some heavy handed
interpolation algorithms involved in reconstructing full color images from Bayer
cameras like the 5D, it's a good idea to look at the resolving power at many
angles and not just the horizontal, vertical, and 45 degree angles you see in
the typical ISO-12223 resolution charts posted on digital camera review sites.
As expected, the 5D takes the lead on resolving power for B/W, but it also
steps ahead on green, yellow, and cyan detail. The 5D's lead starts at
about 24% for B/W detail but that advantage drops to about 18% when capturing
green, yellow, and cyan colors. Due to the lack of a green component, the
5D's lead drops to only a 6% advantage for magenta, less than a 3% advantage for
blue, and actually falls behind to a 4% deficit when capturing red colors
which seem to be the worst case scenario for Bayer sensors. Why?
While red and blue sensors are spaced identically on the sensor and one would
expect the same resolving power for red and blue, blues fair a bit better simply
because they often carry a weak green component, meaning that it is easier to
find reds with no green component than blues with no green component.
While on average, the 5D does seem to have a 10% to 15% advantage in
resolving power, by the numbers (megapixels in the final images), you'd expect a
65% advantage in all directions. The use of antialiasing filters and the
complex color reconstruction algorithms are the primary reason that the 5D
cannot realize the full 65% advantage. It is also important to note that
while in some cases, the 5D pulled better max resolution than the SD14, the
detail at that cutoff point was often very soft due to the amount of
interpolation going on. In contrast, the SD14 was able to carry sharp
detail all the way to its max resolving power, however, as a result of the lack
of "smoothing" being done, the SD14's tradeoff was an increase in aliasing at or
beyond max resolution. A tradeoff for sure. The worst part of the
test for the 5D is that with resolving power varying by as much as 25% for some
colors, the eye can pick up on the fact that some detail in the photo just isn't
as sharp as it should be when the photo consists of subjects with widely varying
color. The SD14's consistent resolving power give photos a more 3D
appearance. It is important to preserve the relationship between detail,
sharpness, and depth-of-field throughout the photograph and this is where Bayer
cameras fall behind by not being able to reproduce the same realism as a full
capture sensor under many shooting conditions. This effect is quite
noticeable on the tests above as well as in real shots. If you look at the
RGB chart for the 5D versus the SD14, the 5D makes the red and blue swatches
look as if they are disconnected from (either in front or behind) the rest of
the chart due to the obvious inconsistency in sharpness. The SD14 shows
consistent sharpness all the way around as it should, and you can tell that all
colors are on the same piece of paper.