sudden brightness jumps

[carmatic]

hey guys
abit about what i am trying to do...
i was making these time lapse photography videos where a few hours can look like its passed in a few minutes or seconds, by setting up my camera to sequentially take a picture every 10 seconds or something

now, the individual frames of this movie would be superb, since they are very high resolution pictures, taken at a low ISO setting with a long exposure and on a camera that's perfectly still...

the problem is, camera seems to arbitiarily decide the resulting brightness of each frame... most of the time it leaves it alone, but when the brightness of the scene goes below or over some thresholds i have no control over, it would brighten or darken the picture automatically.... so i end up with these brightness jumps and dips in the video...

is there a way to fix this? i have tried MSU-deflicker and Fizick's deflicker.... the MSU one seems to take care of the small variations in the brightness between frames but does nothing for the major jumps...
and when i use Fizick's deflicker and make it show the stats on the output, i can see that the standard deviation of the video's mean luma (scroll down here http://avisynth.org.ru/deflicker/deflicker.html) is constantly higher than when the brightness jumps are actually occuring...


so how do i fix this? is it just because i am missing some settings in these deflickers i am already using, or are there better tools out there that i can use?

::edit:: i am taking photos of the sky, and the movement of the sun, moon, clouds, and other stuff up there, so the scenes i am recording have naturally smooth and continous variations in brightness, and the camera's brightness jumps are very obvious

[rgs_uk]

Do you have the exposure on manual or auto on the camera? Auto exposure is the problem I think.

[carmatic]

i have no control over the exposure, besides the pictures are already taken and now i have to do something about them...

it cant be that difficult, right? its just matching the overall brightness between frames....

[redwudz]

About all I can suggest is to look to a VirtualDub filter list like this and try a few: http://www.thedeemon.com/VirtualDubFilters/

Maybe a auto levels filter or use a histogram to try to see the brightness levels?

And welcome to our forums.

[jagabo]

it cant be that difficult, right? its just matching the overall brightness between frames....

It can be much more complicated than you think.

Suppose you have a perfectly exposed scene with an average intensity of 100 (out of a range of 0 to 255). Somebody wearing a bright (intensity 200) white t-shirt walks into the foreground but the camera doesn't adjust the exposure. The background is still the same intensity as before but the frame's average intensity much higher because of all the bright white t-shirt pixels. An algorithm that simply adjusts the image so that the average intensity remains constant will darken the background.

Or suppose you have a five pixel image with intensities 0, 50, 100, 150, 200 -- an average of 100. Suddenly the camera decides to double the exposure time. The pixels would become 0, 100, 200, 300, 400. But the range of intensities can only be 0 to 255. It ends up saving the values 0, 100, 200, 255, 255 -- an average of 162. So your average-intensity algorithm decides to multiply the intensity of each pixel by 0.62 (~100/162). The result is 0, 62, 124, 158, 158. Portions of the picture have become darker and portions have become brighter.

Add to those types of situations the fact that the auto exposure algorithms used by cameras may not be linear, may adjust the black, white, and gamma levels, may weigh certain portions of the frame more than others, etc., and you have a very difficult problem.

If the deflicker filter has an option to limit the brightness analysis to only part of the frame (but performs the adjustment to the entire frame) use it on a portion of the frame that doesn't otherwise change and is mostly medium intensities. Disable any smoothing functions that prevent the adjustments from happening instantaneously for each frame.

[carmatic]

And welcome to our forums.

thanks....

and i think i might have overlooked a very important deflicker tool... D.Graft's one... it gets rid of pretty much all of the jumps, but i guess its not just the brightness that my camera is changing because theres abit of slightly psychedelic-looking chroma shift thats left behind, but thats acceptable...

[jagabo]

You might try the Temporal Smoother filter to reduce the chroma shifts. Or try the VHS filter which can smooth only the chroma channels.

[lordsmurf]

You need to use a better camera. Sorry.

[carmatic]

I have tried Temporal Smoother but it smears out the movement for me...but at low levels its great for getting rid of noise

another way i tried was to use motion blur, a soothing effect but i got bored at how bland it makes the videos look, its better to correct the problem than to mask it with some effect

I'll have a look at the VHS filter... the camera has a nasty habit of shifting the white point the moment it enters its automatic 'night mode'
does this filter depend on some repeating effect or can it work with individual events?
because i think that the deflicker filters i have been using are meant for repeating brightness variations like a film projector, the D.Graft filter gets rid of most of the jumps but it still misses one or two, the help file talks about flickers in terms of duration in numbers of frames instead of thresholds of luma or brightness values.... and the other two filters i have tried also seem to work on a temporal basis as well, single obvious jumps are missed but subtle variations over time are smoothed out

but yeah, on a more complicated scene like people walking across the view, the brightness variations would be tricky to correct, but it wouldnt look that out of place if the scene is complicated in the first place...
but what im working on isnt supposed to have any discontinous variations , unless something falls in front of the camera, or a balloon suddenly floats into view, or if a fire broke out downstairs, or i trip over the power cord and pull my camera off , that kind of thing....

[jagabo]

I have tried Temporal Smoother but it smears out the movement for me...but at low levels its great for getting rid of noise

Yes, ghosting is really bad over 7. You get some ghosting in dark areas at even lower values.

I'll have a look at the VHS filter... the camera has a nasty habit of shifting the white point the moment it enters its automatic 'night mode'
does this filter depend on some repeating effect or can it work with individual events?

A lot of the deflicker filters are designed for use with film telecined by pointing a video camera at a projector or screen. The exposure varies over time depending on the sync between the projector and the video camera shutter leading to a periodic flicker.

The VHS filter is designed to remove VHS noise which varies from frame to frame and pixel to pixel. It does not remove long term variations in brightness or colors. I don't know if it will work for you but it's worth a try.

[carmatic]

ok the combination of D.Graft's deflicker and the VHS filter works a charm

before: http://uk.youtube.com/watch?v=IPgdpXElatk
after: http://uk.youtube.com/watch?v=YQPruLJ8Z_M

sorry i couldnt keep the camera still enough, it kept falling off its stand or it would jam up by itself and i had to power it off and on again.... but you get the gist of it, the camera goes from no daylight to being directly exposed to sunlight... you can see it trying to compensate for the different intensities of light on the first video

the filters got rid of the flickering on the second video, and somewhat improves the colours too, maybe without the flickering the compression can concentrate more on what really matters, or the VHS filter's temporal colour smoothing has managed to compensate for the camera's colour deficiency ... but the VHS filter also seems to cause the clouds right before the sunrise to go all blocky and stuff.... not very obvious in youtube, but the easiest way i can describe it is that it makes the clouds stay darker for longer, then abruptly get brighter, if you can visualize that....

[creakndale]

Very nice results!

I have a surveillence DVR and the cameras are constantly adjusting their gain for varying brightness which causes the motion detection to trigger. 80% of the video captures are due to a change in brightness which the DVR "sees" as motion.

Every once in a while, for fun, I put the DVR in a time lapse configuration when unique weather is moving in. I'll have to keep your filter choices and process in mind the next time I make a time lapse video from the DVR video captures.

Thanks,
creakndale

[carmatic]

i have stretched the window size in D.Graft's filter to over 20 frames to smooth out the brightness across the video, and im using the VHS filter on its default settings... maybe if i tweak the 'temporal error' settings i might be able to get its behaviour to deal with the clouds im photographing properly...

http://flaxen.edwardk.info/
flaxen has another filter called 'Stabilizer 2.1' , no documentation is provided and he claims that its evolved from the VHS fliter... im not sure if i will ever use that, it means encoding another copy of the same video for every different setting i try, and trying to spot anything thats changed as a result... for some reason virtualdub never actually plays videos for me, the only way i can watch anything is to save everything as videos and watching them from another video player...

[sanlyn]

The NeatVideo filter won't fix the brightness levels, but it cleans huge amounts of chroma noise and streaking, and can even alleviate digital artifacts somewhat. It also has a temporal filter that helps a bit when set to 15 or 20%. NeatVideo does cost some cash (it's worth it) and takes experimentation beyond its default settings to get what you want. I gave up on almost every VirtualDub noise filter when it comes to noise reduction for VHS; they seem to cause more problems than they solve.

[carmatic]

noise isnt my problem, at least until i start using those filters... if i change the brightness in a compressed jpeg, there will be blocky artifacts... and the camera's natural noise is stronger than the smooth parts of the scenes... flaxen's VHS filter wont take away all the noise without taking some of the scene with it and leave trails all over the place, and it wont leave most of the scene alone without exaggerating the noise which goes above the threshold... and the thresholding also makes smoothly changing colours turn into steps of a few different colours
i might have to exclude the filter from certain parts of the video, like by using the curve in virtualdub...

anybody got a guide or something on how to use flaxen's 'Stabilizer 2.1' filter?