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Posted by Gene E. Bloch on 10/06/85 11:45
On 4/17/2006, Jan B posted this:
> On Mon, 17 Apr 2006 15:46:34 -0700, Gene E. Bloch <spamfree@nobody.invalid>
> wrote:
>
>> On 4/16/2006, Jan B posted this:
>>> (Sorry I had to work around a FreeAgent limit by move the follow up
>>> upwards in the thread).
>>>
>>> On Sat, 15 Apr 2006 09:45:05 -0400, Tom Stiller <tomstiller@comcast.net>
>>> wrote:
>>>
>>>> In article <4440e4d2.109134196@news.individual.net>,
>>>> nospam@nospam.se (Jan B) wrote:
>>>>
>>>>> When such a camera pans horisontally over a vertical object like a
>>>>> pole and the video is displayed on a CRT that takes nearly a field
>>>>> period to scan from top to bottom I would expect to perceive a tilted
>>>>> object "moving" across the screen. This is since the scanning at the
>>>>> bottom would lag the top when displaying but not at the recording.
>>>>>
>>>>> Have anybody noticed such effects?
>>>>
>>>> You overlooked the effect of the electronic shutter that effectively
>>>> freezes the image before it is scanned out. There is no relative motion
>>>> during the scanning process.
>>>
>>> But that is excactly my point. The case cited above is the case with
>>> freezed momentary picture in the CCD-camera, but the scanning in the CRT
>>> takes time. To get a smooth "momentary strobed" motion over the CRT
>>> surface, the camera picture should be scanned the same way (I think).
>>>
>>> The "moving" vertical pole should have moved to a later position when the
>>> CRT scans the bottom lines.
>>> /Jan
>>
>> The CRT doesn't scan anything, it just displays what the signal says.
>> In this case, the signal says the pole is straight.
>
> By "scanning" I mean that a CRT displays the signal by illuminating the image
> from top to bottom line by line. That takes time (and is designed that way).
>
> The illuminated phosfor fades out in a couple of milliseconds.
> The question here is what happens with perceived motion when the scanning at
> the recording (as in no scanning) and the scanning at displaying is done
> differently. The arguments that claim that the strobed moving picture from a
> CRT is interpretated by our brain as a smooth motion must also consider that
> the moving vertical pole would have moved between the time the CRT scanns the
> top until it scans the bottom.
>
> My thinking is that the strobed moving pole can be perceived as vertical only
> if the camera was scanned in exactly the same way. So a CCD camera with
> instant half field (or frame) storage would give a tilted moving pole when
> displayed on a scanning display.
>
> I suspect that an LCD panel refresh when addressing the panel row by rowalso
> takes time (not discussing slow pixel response here) , so I'm interested to
> know how many milliseconds it takes from top to bottom.
> /Jan
I think you should reread my post and think about it more carefully.
The camera takes a picture in whatever way the camera takes it. That
picture is now a fixed entity which is transmitted to the display
(perhaps through a long pipeline involving recording a tape and playing
it back later, perhaps directly over a wire, or whatever). Now the TV
displays the picture as it was captured. The picture has already been
captured; the TV has no way to change it.
Please think about this.
Gino
--
Gene E. Bloch (Gino)
letters617blochg3251
(replace the numbers by "at" and "dotcom")
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