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Camcorder Resolution and Picture Quality

Let's take a closer look at the internal workings—and image-capture capabilities—of DV camcorders, as they pertain to resolution. (In conventional filmmaking, this would be equivalent to a discussion of camera capabilities and film stocks.) This technical information will be crucial for choosing and deploying the right tools for shooting, data transfer, editing, and distribution.

Digital camcorders are often rated in terms of resolution, and you will eventually need to make a decision about what kind of resolution you require from your camcorder. However, resolution is a complex subject. Even defining it can be tricky.

Spatial resolution generally refers to the number of individual dots, or pixels (short for picture elements) that compose an image. Most of the time, when people refer to resolution, they mean spatial resolution. However, resolution can also be used as a general measure of a video picture's sharpness and detail. Chromatic resolution refers to the range of colors each pixel can show; in effect, it's another term for color space.

No doubt you've seen digital still cameras advertised with "megapixel" capability. For sake of simplicity, if digital pictures were square (which they usually aren't), megapixel spatial resolution would mean an image 1,000 dots wide by 1,000 dots high, totaling a million pixels, hence "mega-."

That may sound like a lot of pixels, but it's still not nearly as good as film. Film has a resolution higher than the human eye can see. Until recently, video didn't even come close. To match the resolution of a single frame of 35mm film, you'd need about 2,000 2,000 pixels.

Some high-priced still cameras do offer 4-megapixel capability or better, but at present there are no megapixel DV camcorders. You need an HD (high definition) camcorder to get into the megapixel range. (For more information, see "HD" in Appendix A.) It's not that electronics manufacturers can't make multi-megapixel devices—they obviously can, and cheaply. But with video, the challenge comes in dealing with the sheer volume of data involved in capturing 24–30 megapixel frames per second (fps).

The more data a camcorder has to process for each frame, the faster it must work, and the more expensive its electronics need to be. So resolution is not only a measure of quality, it's also a good way of predicting cost. High-resolution digital cameras, whether still or video, fetch high prices.

Professional still cameras need maximum resolution to capture images which can then be blown up onto large sheets of film. But there's a limit to the spatial resolution that a digital camcorder requires. For North American SDTV (standard definition television), that's 640x480 pixels; for HDTV, it's either 1920x1080, or 1280x720.

You'd think, then, that a DV camcorder would need no more than 307,200 pixels (640x480) and an HD model would need no more than 2,000,000 (1920x1080).

In reality, however, the effective pixel counts of DV and HD camcorders vary considerably. To understand why, and to make an informed decision about which camcorder with what resolution to buy or rent, some explanation of CCD technology is in order. (For more information, see "CCD Technology" in Appendix A.)

Comparing Resolution and Picture Quality in the Real World

There's a lot to think about when the time comes to choose a camera: resolution, color space, CCD design, aspect ratio, price, and all the rest. So just as an exercise, let's compare three real-world camcorder models to see how they stack up—the Canon XL1S, the JVC GY-DV5000U, and the Panasonic AG-DVX100 ( Figure 3.8 ). These are some of the most popular camcorders among professional videographers and represent interesting tradeoffs between price and performance (Table 3.2). When it comes to technical specifications, the Canon and the Panasonic are prosumer DV camcorders, while the JVC is a professional unit; but any of these models might well compete for your attention.

03fig08.gif

Figure 3.8 The first prosumer camcorder to offer 24P (film look) scanning mode was the Panasonic AG-DVX100, which is also featured in the product comparison in this chapter.

Table 3.2. Comparison of Some Key Specifications of Three Popular DV Camcorders

 

Canon XL1S

JVC GY-DV5000U

Panasonic AG-DVX100

Chip configuration

3CCD

3CCD

3CCD

CCD size

1/3 in

1/2 in

1/3 in

Effective pixel count

250,000

380,000

380,000

Color space

4:1:1

4:1:1 (4:2:2 option)

4:1:1

Shooting modes

30I/30P

30I/30P

30I/30P/24P

Zoom lens

Interchangeable

Interchangeable

Built-in

List price with zoom lens

$4,699

$6,795

$3,795

Effective Pixel Count

When you inspect a camcorder's spec sheet, the first things you'll be tempted to check are the chip size and total pixel count. However, "total pixels" isn't necessarily a good measure of resolution. You really need to know how many pixels actually show up on the screen. This is the "effective" pixel count. Some manufacturers provide this data, some don't.

Canon gives the total number of RGB pixels for the XL1S as 270,000, and its effective pixels as 250,000. JVC's model has 410,000 total pixels on ½-inch chips, with 380,000 effective. Panasonic claims to have the same number of pixels as JVC, but on smaller, 1/3-inch chips.

All of these camcorders are available in the North American TV standard, which requires 307,200 pixels in the displayed picture. You can see that the Canon unit has fewer pixels than it seems to need, the JVC and the Panasonic more. As with any camcorder which has fewer than the required number of pixels, the Canon unit uses a digital interpolation process (essentially, a kind of mathematical approximation) to produce the missing pixels it needs for the final output. The result can look surprisingly good. All three cameras offer a variety of automatic image-processing functions, which no doubt use some of the extra chip real estate.

Seeing Is Believing

Judging from the combination of effective pixel count and chip size, you might conclude that the JVC camcorder is clearly superior. Some experienced videographers think so. However, your eye might well favor the Canon or the Panasonic. All of these cameras offer consumer 4:1:1 color space, but if you're producing solely for videocassette, DVD, or film transfer, the higher broadcast standard (requiring 4:2:2) need not concern you.

Canon claims its pixels are relatively large and give a better picture. It also offers a proprietary process for digitizing color called Pixel Shift that's supposed to improve picture detail. Do those features make up for JVC's larger CCD chip size and higher pixel count? Where do you factor in the JVC's higher price? Even though these considerations are technical, the answers can be artistic and financial: Which output looks best to your eye for your purposes, and how much can you afford to spend?

The list price of the Panasonic is attractively low by comparison. But before you jump for it, there's something else to consider. Unlike the Canon and the JVC cameras, the zoom lens on the Panasonic is not interchangeable—it's built into the camera body. Although this Leica lens is very good, it can't beat the wide selection of cinema-style lenses available for the other two cameras. (JVC offers a selection of Canon and Fujinon lenses for its ½-inch CCD video cameras.)

You can't decide which camera you prefer by looking at a spec sheet. When camcorders are roughly comparable in features and price range, as these are, you have to compare outputs, features, and feel—in the real world. But here's a hint: Filmmakers seem to favor the Canon or the Panasonic, news crews the JVC.

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