Question about 1440 x 1080

[Dave Haynie]

Originally Posted by Bryan Daugherty

To my knowledge the only cameras out there that use a sensor that is 1920x1080 is the SONY EX1 and EX3. All other cameras get to 1920x1080 through interpolation, stretching, or pixel shifting. All HDV output to 1440x1080 or smaller (think 720p.) This information is based on a video tutorial on the XDCAM EX format and can be viewed at the link below.

Actually, most single-chip HD camcorders have full 1920x1080 sensors... pretty much every one that came after that first JVC. And just about every camcorder ever made has square pixels in the CCD, regardless of the storage format.

It's more complex with 3-chip cameras. In the olden days (SD days), you really needed three full frame sensors, since the main point of 3-chip was to give you full color pixels. But for HD, even subsampled color is brilliant, given the relative size of the pixels. Plus, you pay for full-frame sensors in light-gathering capability... the sensitivity of a sensor at any given technology level is based on the size of the sensor (plus any extra light that might be routed to it via a microlens). So there have been all kinds of arrangements, using half-frame-or-smaller sensors with offset, essentially using 3-chip more for light-gathering advantage than color advantage.

The Sony HVR-A1 has a 4:3 sensor that's about 1920x1440 or so... that yields the nominally 2.8Mpixel that's claimed for the sensor. When you're shooting stills (as if anyone does), you get the full field.. when you're shooting video, it does a 1920x1080 crop for 16:9. All pixels are active .. the "spares" are used in the digital image stabilization algorithms. Think about the 16:9 crop being a movable window, and the stabilization being an algorithm that decides just where to put that window in the sensor, based on montion detection.

When the image is processed for compression, the 1920 lines are downsampled to 1440. As with all formats short of high-end stuff, there's also color subsampling and other stuff going on here, too (4:2:0 in HDV mode, and perhaps additional image processing, depending the light and the mode). So the end result are pixels that are 1.333x wider than they are tall... not too weird for anyone who's been doing SD all these years.

And in fact, important enough that Blu-Ray officially supports 1440x1080 resolution video at 16:9, along with the usual 1920x1080 and 1280x720.

[Chris Hurd]

Originally Posted by Gene Gajewski

I think some (all?) of the consumer AVCHD cameras use full 1920x1080 sensors.

Originally Posted by Bryan Daugherty

No. This statement is not true at all...

Actually, Gene is right, his statement is true. Most single-chip consumer AVCHD (and HDV) camcorders use full 1920x1080 sensors. Cases in point, the entire Canon VIXIA camcorder series. Hope this helps,

[Bryan Daugherty]

Chris ,can you point us to any source material that clarifies this? According to B&H's tutorial on the XDCAM format, the only camera's they have in the store with physical pixels that count 1920x1080 are the EX1 and EX3. Beyond that, i am having difficulty finding any information on physical pixel counts on the sensors of any Vixia cameras. While this may be a minor point, i still find it hard to believe that the vixia circa $600 cameras have sensors the same physical resolution as the EX1/EX3 and don't utilize the methods other HDV cameras use such as pixel stretching and pixel shifting. Could you give us any links to clarify this? Thanks.

[Dave Haynie]

Originally Posted by Bryan Daugherty

Chris ,can you point us to any source material that clarifies this? According to B&H's tutorial on the XDCAM format, the only camera's they have in the store with physical pixels that count 1920x1080 are the EX1 and EX3. Beyond that, i am having difficulty finding any information on physical pixel counts on the sensors of any Vixia cameras.

You have to actually try before you can claim trouble. The first place I'd look (since that's where I looked) would be Canon's web site, if I want to know Vixia pixel counts. Go here: Canon U.S.A. Choose "camcorders", then "consumer", then find your Vixia of choice, and click on the "Specifications" page. Took me about a minute, including the time to read this post.

This would be telling... but hey. So I look up "Vixia HF S11", and I find these stats:
Image Sensor
1/2.6-inch CMOS, RGB Primary Color Filter
Total Pixels
Approx. 8.59 Megapixels
Effective Pixels
Video: Approx. 6.01 Megapixels (3264 x 1840)
Still Image: 16:9 Approx. 6.01 Megapixels (3264 x 1840)
4:3 Approx. 8.02 Megapixels (3264 x 2456)

So, in English, that means the 16:9 crop of the sensor yields a 3264 x 1840 image, which is downrezzed in software to 1920x1080 or 1440x1080, depending on your selected recording mode. I guess actual 1920x1080 sensors are "so last year"... well, the HF200 yields 2304 x 1296 from the sensor, while the HG's still deliver a true 1920x1080.



While this may be a minor point, i still find it hard to believe that the vixia circa $600 cameras have sensors the same physical resolution as the EX1/EX3 and don't utilize the methods other HDV cameras use such as pixel stretching and pixel shifting. Could you give us any links to clarify this? Thanks.[/QUOTE]

[Bryan Daugherty]

Dave i saw that too but those are effective resolution, which as I understand it is not the same thing as the physical resolution of the sensor.

For example using the cameras listed before, the physical resolution of the sensors in the Sony HVR-Z1 camera are 960x1080 but the effective resolution is 1440x1080 after pixel shifting. The Panasonic AG-HVX200 has three 964x540 pixel sensors that after pixel shifting and pixel stretching result in an effective resolution of 1440x1080. These are of course, HDV cameras, not AVCHD cameras.

I did actually try and all I can find are effective resolution stats. And so did you.

Originally Posted by Dave Haynie

You have to actually try before you can claim trouble. The first place I'd look (since that's where I looked) would be Canon's web site, if I want to know Vixia pixel counts. Go here: Canon U.S.A. Choose "camcorders", then "consumer", then find your Vixia of choice, and click on the "Specifications" page. Took me about a minute, including the time to read this post....

[David Heath]

Originally Posted by Bryan Daugherty

According to B&H's tutorial on the XDCAM format, the only camera's they have in the store with physical pixels that count 1920x1080 are the EX1 and EX3.

It's a case of whether you are talking about single or three chip 1920x1080.

In Chris's case, he does state single chip - I suspect that B&H are referring to three chip cameras, each chip being 1920x1080.

In the single chip case, half the pixels will be green, and a quarter each red and blue. A debayering process yields a Y,U,V raster out of that. But even if the output is 1920x1080, the debayering will inevitably mean that the luminance resolution will be nowhere as good as if the 1920x1080 chip was simply used in a monochrome fashion, or if three 1920x1080 chips were used.

To get the resolution equivalent to three 1920x1080 chips from a single sensor, that must have a pixel count greater than 1920x1080, and then downconverted. A reasonable rule of thumb would be about twice the pixel count of the output raster, or in this case around 4 megapixel.