Mailing List Archive

On Thu, 2009-02-12 at 16:18 -0500, WSD33904 wrote:
> I am pretty new to the ivtv driver for Linux, therefore I am not too
> familiar with the different configurations for ivtv. But anyways, I am using
> MythTV and I am having a few problems with the quality of the picture. I
> have checked recording quality profiles, TV signal (very good signal,
> actually), and little things like that. I have narrowed down the quality
> problems to the card itself.


> There isn't a lot of sharpness in the picture,
> and objects in the background of the picture aren't as sharp as I think they
> could be.

You may want to experiment with the compression controls:

$ v4l2-ctl --log-status

to see the current settings, and

$ v4l2-ctl -L

to list all the controls you can change.




> Also, an annoying dropshadow of green or red or purple are
> constantly surrounding people in the picture. Could this be due to any
> sudden color changes in the picture between the people and the background?

I'm not quite sure what you mean by "dropshadow" but it sounds like a
strong signal reflection somewhere in your cabling. Color in NTSC is
determined by the timing of the signal relative to the color carrier
phase (IIRC). A delayed copy of the signal would explain an off-color
copy as a shadow.


> Are there any commands that could help me improve image quality? Any and all
> suggestions are appreciated.

These aren't commands, but may be worth double checking:

http://www.ivtvdriver.org/index.php/Howto:Improve_signal_quality

Regards,
Andy



> If anyone would like a screen capture, I would
> be more than willing to send a link with an image. Thanks!
>



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Andy:

>I'm not quite sure what you mean by "dropshadow" but it sounds like a
>strong signal reflection somewhere in your cabling. Color in NTSC is
>determined by the timing of the signal relative to the color carrier
>phase (IIRC). A delayed copy of the signal would explain an off-color
>copy as a shadow.


Here is a link that has an example of the image quality problems that
I am experiencing. You responded to my question in issue 9 of the IVTV
mail list (February 13th)

http://www.mythtvtalk.com/forum/ivtv-issues/10841-pvr-150-mythtv-capture-quality-issues-picture-included.html#post44262

If anyone has any comments, please do not hesitate to express it!

Regards,
Maury

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On Mon, 2009-02-16 at 15:04 -0500, WSD33904 wrote:
> Andy:
>
> >I'm not quite sure what you mean by "dropshadow" but it sounds like a
> >strong signal reflection somewhere in your cabling. Color in NTSC is
> >determined by the timing of the signal relative to the color carrier
> >phase (IIRC). A delayed copy of the signal would explain an off-color
> >copy as a shadow.
>
>
> Here is a link that has an example of the image quality problems that
> I am experiencing. You responded to my question in issue 9 of the IVTV
> mail list (February 13th)
>
> http://www.mythtvtalk.com/forum/ivtv-issues/10841-pvr-150-mythtv-capture-quality-issues-picture-included.html#post44262

Well the failure mode looks somewhat obvious: the digitizer (like at
CX25843) is not getting set up right or it's being reverted to the
autoconfig defaults-.

All the analog front end gain adjustment and analog to digital
conversion happens at the digitizer chip. The black with white pixels
lines at the top are Vertical Blanking Interval test signals and data
services (like Closed Captioning). Either the digitizer isn't detecting
vertical sync properly or the digitizer register for the number of lines
of vertical blanking isn't being filled properly. The digitizer has
other filters and gain controls that can be applied to an analog signal.

I2C bus errors/failures could cause registers in the sigitizer not to be
programmed properly.


When the machine is realtively quiescent, kill the mythbackend, use
modprobe -r ivtv cx25840 to unload ivtv and the cx28540 (or whatever
digitizer you have) modules. Then modprobe ivtv and see if things are
better.

Regards,
Andy

> If anyone has any comments, please do not hesitate to express it!
>
> Regards,
> Maury
>
> _______________________________________________
> ivtv-users mailing list
> ivtv-users@ivtvdriver.org
> http://ivtvdriver.org/mailman/listinfo/ivtv-users
>


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