Product Review
 

JVC GZ-HD7 HDD (Hard Disc Drive) Three-Chip High Definition Video Camera

Part III

October, 2007

John E. Johnson, Jr.

 

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. -

© Copyright 2007 Secrets of Home Theater & High Fidelity

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