|
|
Posted by Jan Panteltje on 11/08/07 14:08
On a sunny day (Wed, 7 Nov 2007 23:19:14 +0000 (UTC)) it happened
davem@cs.ubc.ca (Dave Martindale) wrote in <fgth5i$mc4$1@swain.cs.ubc.ca>:
>"Joe" <abc@xyz.com> writes:
>>So, back to my original question- was Spex right when he replied to someone,
>>"What are you so hung up about capturing at 1920x1080 when the actual
>>resolution of the camera is way less than that at 800+ tvl?"
>
>Assuming that "800 tvl" means 800 TV lines per picture height, as it
>usually does, and that this was measured in a 16:9 image (which is what
>I'd expect for any 1080-line image), then the horizontal resolution is
>about 1420 lines per picture width. This is pretty much the maximum
>resolution possible at 1440 pixels horizontal.
>
>Now, if the 800 TVL resolution is measured from the HDV data being
>played back, where the stored image is only 1440 pixels wide, I'd
>suspect the resolution limit is due to the storage format.
>
>On the other hand, if you get 800 TVL right off the sensor via the HDMI
>output, that says that the lens/sensor resolution is only just good
>enough for the 1440-pixel recorded format, and capturing at 1920x1080
>won't give hardly any additional detail. In that case, Spex is right -
>there's little point complaining about recording at 1440.
>
> Dave
It is a bit more complicated then that.
This camera, the HV20, is a single sensor chip model.
To get color, the chip's sensor elements are covered by red, green, and blue
filters:
http://en.wikipedia.org/wiki/Bayer_filter
Likely Bayer patterns (as Canon mentions 'simple RGB' in their specs).
Just this fact, in itself, sort of reduces the luminane resolution by half the horizontal pixels, see:
http://www.cambridgeincolour.com/tutorials/sensors.htm
This is a consumer camera.
Canon mentions optical stabilisation, but in many consumer cameras there is also
digital stabilisation, the way that is done is the picture is projected on
a smaller area then the full sensor, so it can move about horizontally and vertically,
allowing for the electronics to move processing along with it, resulting in a stable
picture.
Such a scheme further reduces available resolution.
I am not sure if the HV20 also has some digital stabilisation.
If you really wanted 1920x1080 Y you would need a 3 sensor camera, or one with
those chips that have R, G. and B behind each other (but not sure you can buy those).
There are 2,960,000 pixels, but those cannot all be used in 16:9.
As to the measured resolution of the HV20:
http://images.camcorderinfo.com/images/upload/Image/Canon/Canon%20HV20/Video_Performance/3000lux/Canon_HV20_3000lux_24P_vivid.jpg
quote:
In 1080i, the HV20 showed a vertical resolution of 575 lw/ph and a
horizontal resolution of 625 lw/ph. In 24P, the camcorder actually
improved the vertical resolution, producing less break-up and
artifacting in areas of high-density information, boosting the vertical
resolution up to 600 lw/ph. The horizontal resolution remained unchanged
at 625 lw/ph.
end quote
And more info here, also on low light:
http://www.camcorderinfo.com/content/Canon-HV20-Camcorder-Review/Performance.htm
http://www.camcorderinfo.com/content/Canon-HV20-Camcorder-Review-Complete-Color-Charts.htm
So, although this really is a NICE camera, it is in no way 1920x1080 HDTV.
But it gets worse, playing the 1440x on a true 1920x1080 LCD reduces detail further
due to re-sizing in that LCD (or call it aliasing) as 1920 / 1440 = 1.333.. and every so
many pixels some artefact will appear as unsharpness (I should take a picture of this effect
some day, but it is clearly visible on small text, also on moving fine patterns).
Then there is a third issue, most of these high res LCD TVs today are 60 Hz, even my monitor,
this causes horizontal jumping in PAL land, where it is fed with 50 Hz.
Any comments?
Navigation:
[Reply to this message]
|