Correcting vignetting and hot spot in post production
 

I'm not completly sure if to post this here or in the post production section.

BTW

I was considering the option to correct the hot spot, that some homemade 35mm adapters gives, using some digital filters like this free one

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

I can't try it because works for Windows only and I'm a Mac user.

Is there any Windows user volunteer that can try it ?

My hope is that somebody, like Graeme Nattress, makes a similar plug in for Final Cut (hopely for an affrodable price).

You can "fudge" it yourself -- shoot a white, evenly lit, flat surface for a few seconds with your adapter. Then, bring this footage into FCP, and play with the brightness/contrast/sharpness, until you come up with what looks like a good representation of the hotspot. Then, using layers, stack this as a mask between two copies of your footage, "projecting" one (brighter or darker) down onto the other, through this mask. You will have to play a bit to get it right, but it's an ok solution sometimes.

Since I just built an adapter, I added a Rotation function to a few of my video software applications. A vigneting compensation is also in the works to be integrated seamlessly with the apps. The suite of programs will be released shortly, as I am in the final beta stages.

The only thing is that my software is for Windows.

Keep an eye for the tungsten|SOLID suite. I am sure you will be nicely surprised :)

Thanks Jim, as a Final Cut user I'm still a learner but I'll try to do it.

Alain, you get exactly what I mean, a suite of filters ready to use that makes easier the postproduction if you shot with a 35mm adapter.

My hope is having soon a suite like this for FCP and FCE too.

if you create a mask in a circle with feathered edges then play with its transparencies properties, it should do the trick. i've seen it done before on some really old 35mm adapter footage.

I've tried that VirtualDub plug, and the big problem with it is that you often don't have an image shot on a white background. I wasn't satisfied with the result.

The principle described by Jim Lafferty is the way to go. Half a year ago I used this principle and managed quite well getting rid of vignetting in Sony Vegas. The key is the godsent effect Cookie Cutter which actually is a mask generator that allows you to cut out areas using basic geometry.

I copied the clip to two tracks, one exactly above the other. The lower track will remain ontouched. On the track above I first added "brightness/contrast" to brighten up the dark edges to match the levels of the hotspot. Then "Cookie cutter" is applied, cutting out the middle (the "hotspot"). Everything around (the vignetted area) is kept. Size, position and feather is then adjusted in Cookie cutter. Then the brightness/contrast is tuned a little. Then maybe some more tweaking has to be done in cookie cutter. And so on. When you've done it a couple of times it's quite easy, and often the same vignetting appears on different takes, so the cookie cutter can be copied to multiple clips.

The pro with this method is that no mask have to be created in photoshop or similar. Making the "mask" with cookie cutter is so much easier because you work directly with the image. Download the Vegas trial and try!

Carl,

That is a great tutorial - you should put it up on the Sony site somewhere for all to see!

I have a question about post production vignetting correction. I haven't tried the white paper method yet but wouldn't that cause increased noise in the vignetted area?

Don't forget the Diaconu'ian method by using a central grad ND filter in front of the lens (either on the DV camera or on the adapter)
You'll loose some light, but gaining brightness in post is not perfect either.

Thanks Leo!

Yes, but you can do some serious noise reduction on the mask.

Agree, but on the other hand, the whole clip will get very dark so you have to brighten in up anyway.

The lesson I've learnt from this is that it is possible to some degree to fix vignetting. But I've gotten tired of it and motivated to get a nice condenser. The raw material should always be as good as possible. Post-production should be for enhancing, not making junk a bit more useful... :)

That's what I meant...If you use the filter in the first place, the image will get a bit darker, but that means you need to add more light to the scene or open up the aperture, not gain in post if possible.
A condenser is very important, but a fast SLR lens is at least as important. My 1.4 - 50mm lens has a tremendously better light spread than my 1.7 - 50mm lens.

Tutorial!
 

I wrote a tutorial about fixing typical adapter issues in post. The vignetting part is finished and it's also the most "manual" part. I'll continue writing now, but feel free to check it out even though the rest isn't finished. Comments, tips etc are welcome!

http://www.nattvard.com/35mm/fixing/

I expect everyone finding this useful to reply!



One comment on the first post, I'm switching to Mac, but for some applications you can't live without a pc. I've tried to find similar tools like the ones I used in the tutorial for Mac, but without success. Therefore I'm keeping the pc as a slave, doing dirty work like this. :)

Great job Carl, Very clear. Thank you

Tutorial finished
 

The tutorial is now finished
http://www.nattvard.com/35mm/fixing/

* Vignetting removal in Sony Vegas
* Stabilizing & Flicker removal in VirtualDub
* Cropping & Sharpen in VirtualDub

Clip is here, http://www.nattvard.com/35mm/fixing/gay_02_xvid.avi
1. Original, deinterlaced (section 4)
2. Devignetted in Vegas (section 5)
3. Stabilized, deflickered, cropped, sharpened in VirtualDub (section 6-7)
4. Magic Bullet added (not in tutorial)