Auto-Levels / Mike Crash / Better approach?

RichMacDonald wrote on 1/24/2006, 1:44 PM
As much as I use and love the noise reduction filters from Mike Crash, I am disappointed in the "auto" part of the Auto-Levels filter. I don't understand exactly what it does, but I can't use it because it adds "flashes" by adjusting the overall levels very rapidly. My goal is to use the filter to automatically expand the levels to a min/max range, but it must also dampen the adjustments so it doesn't look like someone is "riding the brightness knob a couple times a second".

Possibly I'm suffering from ignorant user syndrome. If anyone has figured out a good way to use this filter to automatically adjust the levels, I'm all ears.

I mention this because I'm spending the day writing some java code for the Sun "JAI" (java advanced imaging) package. One of the available functions is to take any image and adjust its levels to match a given histogram. (And of course I can take any image and use its histogram as the "standard".) That is a very powerful feature that I haven't seen elsewhere (if I have I never recognized it :-) I have yet to write the code to evaluate this feature so I cannot claim how it looks visually, but I suspect being able to "clamp the histogram" is a useful technique.

Actually, I'd like to "clamp the histogram" then add a PID controller to allow adjustable short-term excursions (e.g., when the dark-/light-shirted idiot walks in front of the camera). That would be slick.

P.S. The sun tool is for programmers-only and for stills-only, so no chance of me writing a vegas plugin, I'm afraid.

Comments

Jøran Toresen wrote on 1/24/2006, 1:56 PM
Pinnacle / Avid Liquid Editon has some great colour correction tools. One of them is called Histomatch (if I remember correctly) and this filter can match the colours in different clips using the Historgrams. Is this what you are looking for?

Joran
RichMacDonald wrote on 1/24/2006, 2:03 PM
>Pinnacle / Avid Liquid Editon has some great colour correction tools. One of them is called Histomatch (if I remember correctly) and this filter can match the colours in different clips using the Historgrams. Is this what you are looking for?

Yes, exactly. Well, that would work for one frame at least. Now if we could apply that to an entire clip...and add user-configurable (keyframeable :-) controls to dampen the adjustments...
Jøran Toresen wrote on 1/24/2006, 2:53 PM
You can do that in Liquid Edition.

Joran
Laurence wrote on 1/24/2006, 3:47 PM
Here's a link to an AVISynth script that normalizes video levels:

http://strony.aster.pl/paviko/

Coursedesign wrote on 1/24/2006, 4:27 PM
RMD,

Are you really looking for something to do the equivalent of in-camera automatic exposure?
RichMacDonald wrote on 1/24/2006, 7:30 PM
>Are you really looking for something to do the equivalent of in-camera automatic exposure?

Oh I already have in-camera automatic exposure ... its just not very good :-)

I've only tried the auto-levels on one project: low light, changing light, and changing scenery. I wanted to see what it would do. What it did was "bounce" the brightness up and down very rapidly, which is very noticeable. So I put the filter away.

Then today I discovered a new capability that had never occurred to me. It turns out to be a well-known technique: a google search on "histogram equalization" shows that. And when I thought about it a bit, it seemed like (1) a possible "auto-exposure" filter for lazy camera operators as you queried, and (2) maybe very important for color matching. If (2) works, and some quick reading says it does, then more "scientific" then "mere" color curves and color correcting filters. Uh, given that color correction is in no danger of becoming pure science :-)

So I thought it would be interesting to bring up for the group's analysis. I'm sure others have already used such a filter (not in vegas). Does it work? What are its limitations? For its power, it should be quite simple to write as a vegas plugin.
Xander wrote on 1/24/2006, 8:07 PM
Filmed a bit of stuff for my brother's wedding in Finland last year - couple of minutes. An outside scene, which looked blue, turned into daylight using Mike's filter - awesome. An indoor shot which panned passed a window, produced an undisarable effect across the window, but the rest looked awesome. The best way to use Mike's filter is to clearly not have extreme light changes during a shot. All in all, Mike's filter produces better results than worse, but then again, nothing that is fully automated will do anything better, as much as we would like too - everything has a sweet spot.
DJPadre wrote on 1/24/2006, 9:29 PM
what the auto levels plug needs is a LOCK function... find the correct WB and then LOCK those levels for the whole clip..