On the Bench
First, let's look at the lens falloff. For wide angle shots, the falloff is
really quite low, in fact, excellent.
And as to falloff in telephoto, it's superb,
with only 0.18 f/stop loss at the corner.
The gray scale noise chart is shown below. The
first graph shows why there is highlight blowout, as the line follows the
first order pretty closely. Some camera manufacturers have the sensor output
drop off non-linearly in the highlights so as not to blow them out.
The second graph shows that noise reaches 0.6%
in the darkest region of the gray scale. This is the first time such graphs
have been published in consumer magazines regarding video camera sensors, so
we will have to wait until we have a few more video cameras reviewed to make
any comparisons.
Chromatic aberration is not too bad, at 1.04 pxels.
This color chart is a TV standard. The GZ-HD7
reproduced it somewhat too blue. Automatic White Balance was used (for all
the tests), and even though it is not quite correct, the color balance can
be adjusted in any video editor before you burn it to a DVD.
The ColorChecker SG test chart indicates that,
like all digital cameras, the recorded colors are a bit off from the
original. In the test result below, the upper left corners are the original,
and the bottom right corners are how the GZ-HD7 reproduced them. Again, I
don't have results from other video cameras yet to compare these results to.
And, finally, the MTF50 resolution test. Again,
there aren't any such data for other video cameras for comparison yet, but
it is apparent that the GZ-HD7 is not as high resolution as it should be, at
a little more than 200 LW/PH (Line Widths per Picture Height). Surely, part of this issue is the fact that
the photo is from two interlaced fields that were not taken at the same
instant in time. The image is not over-sharpened though.
Keep in mind
that this resolution test (MTF50) takes into account both the lens and the sensor,
and does not simply detect how many lines there are. Rather, it is a
standard reference for a specific contrast level between lines.
A diagrammatic representation of the MTF50
criterion is shown on the right. The left portion shows adjacent black and
white lines at 100% contrast. In a photograph of black and white lines of
decreasing spacing, there will be a point where the contrast between the
lines is 50%, shown in the right hand portion of the diagram. This is the
MTF50. It will specify how many of those lines (each black line counts as
one line, and each white line counts as one line) it would take to go from
the top to the bottom of the image (Line Widths per Picture Height). Thus,
the pixel dimensions of that image are part of the consideration.
This means you can look at a test result on a
specific image, and knowing its dimensions, e.g., 1920x1080, determine how
well that camera sensor and lens combination performs. In other words, the
perfect 1080i camera sensor and lens would give a result as 1080 LW/PH,
assuming the camera were held perfectly still. Since there will be at least
a little dispersion at the sensor itself, and certainly some in the lens -
which affects contrast - and also other lens aberrations, the resulting LW/PH
is usually going to be quite a bit less than 1080, at least for 1080
consumer cameras. So, the MTF50 is a
criterion we all need to get familiar with in camera tests.
Conclusions
The JVC GZ-HD7 HDD is a high definition video
camera with exemplary features and is very easy to use. It will need some
software updates from video editor programs in order to fully recognize the
new file extension, but it is still workable even now. Although the color
quality is excellent - due to having three separate sensors - the resolution
leaves something to be desired. For those consumers who are more interested
in having features and ease of use, this one is really good. But for those
who are searching for the ultimate in picture sharpness for their high
definition videos, keep searching.
- John E. Johnson, Jr. -