removing hotspots when transferring super8 to dv

[thoralf]

Hi there,

When transferring super8 (yeah, this old-fashioned, alwyas out-of-sync-stuff) to a more up-to-date medium unsing the cheapo-way of doing it (i.e., capturing with a dv), one inevitably faces hot spots: a circle in the middle of the picture that is way too bright vs. way-too-dark spots in the edges (caused by the projector's lamp).
Is there a way to get rid of this effect with avisynth? I thought about using a semi-transparent mask (a simple circle with an alpha value of 50% or something), but that's overstraining my scripting capabilities a bit ...

Thank you for your help,
Thoralf.

[rfmmars]

The problem that you want to solve can not be fixed. It is due to the high dymanic range of film and the low dynamic range of your DV camcorder plus other things. The AGC system of your camcorder is adding to this problem.

You need to make a custom projection screen and its not too hard. In a paint program create a circle gradient going from dark gray in the center to much lighter at the edges. This will help solve the burn out faces that appear in the center of the screen. Print this out on the best inkjet printer you can find at the highest resolution. Print using Epson's bright white high resolution paper - NON GLOSS -

Next step is to use a different camera, either a Panasonice or Mintron CCTV camera with extended dynamice range 270:1 compared to a DV camcorder's 30:1. ACG off - MANUAL white balance The lens is to have an manual adjust iris. This option in not cheap Camera $279.00 US. and the F1.2 TV 12 - 85 mm zoom lens $800.00, so try the screen first.

After that you will still need to apply a hot spot Avisynth filter or a VD radial luminence correction filter plus white balance and sharping.

You can go to my website www.photorecall.net for further info.

richard

[Fizick]

Try
Super8equal plugin for Avisynth
http://www.geocities.com/belgabor/avs/

or Hotspot plugin (for VirtualDub probably ?)

[thoralf]

Thank your for your quick answers. I'll try the custom projection screen and will get back with the results ...

With kind regards,
Thoralf.

[Cyberman]

There is a VirtualDub filter for that:

http://neuron2.net/hotspot/hotspot.html

Also, the Histogram equalizer could help:

http://neuron2.net/histogram.html

Both are VDub, though.

[thoralf]

I'll have a look at the vdub-filters as well ...

@rfmmars:
what sort of gray should I use? I guess that the answer depends on the projector, but still, do you have a rule-of-thumb for that?

Thank you again,
Thoralf.

[rfmmars]

For the center I would choose a medium to dark gray. My paint program allows me to choose the two gray levels for the circle or oval gradeint. You will want to blur the entire page so the transistion from level to level is not noticable.

Also if your video image hasn't enough red, green or blue, then you can use the lacking color instead of gray, trial and error. If you download the Hot spot VD plugin, on the web page, it gives you a good idea what the pattern should look like.

I shoot about 14" from the screen.

richard