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Old August 16th, 2004, 07:48 PM   #1
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Maximizing Dynamic Range

Hi everyone,

I have been wondering lately if could be possible to utilize a technique from still digital photography to improve the dynamic range of an image beyond that of 35mm color film (not sure about B&W).

I have seen still photographers combine several images - one exposed for highlights, one for blacks, and one for midtones - into a perfectly exposed single image.

Granted, this can't work in video as it would in still photography as we can't easily take several different shots of the same thing and expect them to overlay perfectly.

(btw, it occured to me that you might be able to do this very simply with the color correction tools built into most NLE so this may be a completely stupid and roundabout way of accomplishing this).

Therefore, I was thinking that it would be easy enough to do this with one RAW image. If one exposed for the midtones (while maintaining highlight information) you could easily duplicate this footage several times and adjust each individual parameter. For instance you could bring up the midtones with a curves adjustment layer, select the highlights by inverting the image, applying a 1 pixel gaussian blur, and use this as a mask.

Am I just being stupid?
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Old August 16th, 2004, 08:35 PM   #2
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I had a similar idea but took it a different direction. Imagine a 3CCD camera where each CCD was instead recording the image in color but at different exposures. The camera would have a built in "zebra-like" feature in the sense that it could tell the parts of the image that where about to clip. Thoughs sections of the image would be omitted and replaced with the opposing video signal from the second CCD set at a lower exposure. Now apply the same concept to the the shadow side of the image and selectively replace the near blacks with the video from a third CCD thats set at a higher exposure. In theory you could increase your stop range by a amazing 3X! All the while no post processing would be needed and it could all be recorded to the same format as before because the resulting image going to tape would be NOT be the sum of three full signals but pieces from all three to adding up to only one signal.

Im taking orders starting 2006 ;-)

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Old August 16th, 2004, 08:38 PM   #3
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That is an interesting idea Brett! Actually I think there is a technology used in some SLRs? that uses a similar idea:

Instead of three chips it contains a distribution of large and small image receptors with which it captures different areas of the image. You loose resolution (but then again the camera I know of that uses it is 6megapixels) but you gain dynamic range.
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Old August 16th, 2004, 09:59 PM   #4
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Well, there are logarithmic sensors available.
They work more or less like this:
every pixel has an added transistor that the higher the signal the pixel gets, the lower the gain applyed to that pixel.
The same applyes for shadows, the lower the signal the higher the gain...
Fillfactory's Lupa line work that way..
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Old August 16th, 2004, 11:11 PM   #5
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Some film scanners employ the multi exposure method when scanning print stocks.
Dalsa had the log exposure too, I remember.
Fuji is doing the different sized photo sites, right ?
-Les
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Old August 17th, 2004, 12:22 AM   #6
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See http://www.debevec.org for lots more on HDR imaging, including a free download of HDR Shop. Also do a search on these boards for HDR; I've posted about the topic several times in the past.
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Old September 19th, 2004, 11:52 PM   #7
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may be Zone system will help

DEar Folks,
I use zone system to define tone when i work with DV, mostly with PANA DVX100 at cine-like, to myself i also stick to 5 stop range i have a conversion between the marker and zone
80% = VII
65% = VI
50% = V
35% = III
25% =II

so if i set up lighting i instentionally make a flat ratio to squezze all detail from hight light ( except hotspot) to shadow into 5 stop range, i have no problem to bring to any contrast or gamma at post.
just like the late Ansel Adams N+1 or N-1 with developer or paper.

the only problem is the orginial DV footage look very dark and dull, and mostly the client they worry a lot and even some directors insist it's too dark, but after all, a TV with higher contrast and brightest for client and a test for director will do.

I am not trained by TV/video, so i only try to make something out of DV or digital beta like film for a lower cost.
many fellow technician claim i mess up the system as they say "oh, it's too dark, too low contrast."
but i am shooting a film with DV, i also don;t do white balance i just set like 5600K or 3200K. this wil give u a unique colour to deal with at colour correction, one set will fit most of the scene.

i recently read and article that even 2 stop under on DVX100, the gamma curve can be bring back to normal, so this is a way to preserve the detail on highlight.

Think FILM, not video.
good luck
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Old September 20th, 2004, 02:34 AM   #8
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well, Yamamoto, I'm a video technician (for video to film works)and I work exactly the way you describe, and I suffer the same things as you do...and I'm in Argentina!!!

So it looks all around the world cine people think the same way :)
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Old September 20th, 2004, 07:37 AM   #9
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The problem with under exposing video is the noticeable increase in noise. when the scenes are lightened to proper levels or tonality. Under exposing also reduces the amount of detail your image will have and can cause banding.

Ansel Adams created his now well know Zone System in the 1930's. He never intended for it to be used with video. Video chips have a different response curve than film and Adam's methods really aren't applicable.
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Old September 20th, 2004, 08:01 AM   #10
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well, it works perfect for me anyway :)
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Old September 20th, 2004, 09:05 AM   #11
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The zone system is a system dealing with Black & white film and developer and paper of it's time, but once you understand it, it's a scale like music, so a simple test or search of the curve will give you the idea easily to work with.

I actually did a feature film with panasonic tiny DV camera, dx-100
i choose to shoot almost everything just at sunrise or about sunset and maniputaed at post to deal with contrast and garde the colour i want. almost no one believe it's DV. they all ask is it film.

noise is the issue that's why i go flat to avoid too dark and bring up from grave.
Tiffen has a filter to soften the contrast ( ultra contrast)

also if ur camera allows to use some lens from earlier which is single coated, e.g i use old nikon lens on mini35 it's work ok.

The cine-like gamma from DVX100 is a trend to camera manufaturer to look at the more dynamic range to response to the film makers who want to use dv as an effective medium to shoot. it helps me to preserve the detail. just like negtive does.

however my friend who used to runs a cable Tv hates film gamma and always prefer 4:3 sharp edge enhance and high contrast.
so it's a matter of taste too. he thinks this is a mistake to make DARK and DULL video.

YAMAOTO
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Old September 20th, 2004, 09:11 AM   #12
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Indeed like Juan writes, Fillfactory (Belgian spin-ff from IMEC) has an active pixel CMOS imager technology which in the future will make it possible for consumer electronic imagers to get dynamic ranges far beyond (100db and more) the film lattide possibilities. Each individual pixel holds an auto gain reduction feature resulting in a real DR compression of scene DR. On the other hand pro cams because of the better (larger...) CCD chips, the more precise initial AD conversion (13bits and more)and signal processing (knee processing..) can go up to 80db DR without excessive noise or banding. Consumer cams seldon go beyond 50 db for an acceptable picture
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Old September 20th, 2004, 12:14 PM   #13
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Back to Brett's idea - why not use a three chip block but have an ND filter pattern on each chip? One clear, then ND3 ND6 ND9.
You'd have to record at a higher data rate to absorb the HDR image, and you'd be interpolating down to a quarter of your actual resolution per colour. But assuming the image wasn't insanely contrasty it should look pretty good.
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Old September 21st, 2004, 07:25 AM   #14
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... the cheapest and most effective way is to use a rotateable gradient ND filter.

I use a ND gradient (-2 stop to clear) which i always carry with me

I also have a gradient mask for it - easily made by shooting a white card with the filter on.

the gradient mask combined with a garbage matte is used in post to pretty much sort out any extreme contrasty conditions
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Old September 21st, 2004, 07:50 AM   #15
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Canon already has a patent on a CCD/CMOS variable DR imaging chip from the early '90's. If I remember correctly, it uses variable CMY dichroic filters to adjust the exposure.
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