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#1 gregory mandry

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Posted 10 August 2007 - 09:44 AM

Just an odd thought has anyone tried flashing using a Varicon or other, on an HD format?

I know in this post production age this will seem like a made question but hell i like in camera.

Anyway just a thought.

Some samples would be really nice top look at.
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#2 Phil Rhodes

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Posted 10 August 2007 - 10:47 AM

Hi,

I've not tried it, but I'd thought about it, and I'd like to. It's an interesting idea. I might try mocking up a rig for it. You'd have thought that doing it optically rather than in post would be particularly valuable in HD given that it pushes the dynamic range around so much.

Phil
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#3 John Sprung

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Posted 10 August 2007 - 12:10 PM

A side by side test with film using the same rig would be the best thing -- It may work quite differently in HD, as the mechanisms are very different. Film grains either expose or they don't, based on how many photons hit them (IIRC, six is the magic number). If flashing adds, say, two photons to every grain, that flips the fours and fives. CCD photosites are generally bigger than film grains, and don't have the binary threshhold. So, this is definitely something where testing rather than speculation is the way to go.



-- J.S.
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#4 Michael Nash

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Posted 10 August 2007 - 05:38 PM

It's not exactly the same thing, but I've used Ultracon filters on SD video before. It ends up with a slightly more "organic" or optical quality that's rather pleasing and less electronic-looking. I think that may be in part due to the fact that it's pushing the tonal reproduction around along a curve that you can't exactly duplicate through pedestal and black stretch controls.

By flashing HD you might be able to get more shadow detail with less noise than you would by lifting the blacks/shadows digitally (in-camera or in post), but of course you'd have to test. But HD really needs the help at the other end of the curve! Unless you're trying to underexpose to protect the highlights, and then flash to recover shadow detail. I suspect you'd end up with a very flat-looking image that would need a lot of color correction, but maybe it's worth a test.
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#5 Phil Rhodes

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Posted 10 August 2007 - 06:11 PM

I tend to agree, but then I very much like the results of shooting fairly (even very) low-con and then recovering later. I'm already able to get a result much lower in contrast than I really need from most cameras, but at the cost of noise.

Phil
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#6 gregory mandry

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Posted 13 August 2007 - 08:40 AM

I have been shooting in the low budget Horror genre and I was wondering about pushing some colour into the shadows using something like flashing but in HD.

So I was just wondering if anyone had tried flashing of any sort just to see if it was a tool we are overlooking.
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#7 Phil Rhodes

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Posted 13 August 2007 - 10:32 AM

Hi,

Okay, so there's basically two ways to do this, excepting firing light directly into the chips from inside the "gate" area, as Kinetta was intended to do with LEDs. Either:

- You build a semisilvered mirror assembly; a beamsplitter to allow you to bleed light into the optical path from a planar source at right angles to the lens. The minimum light loss is probably about a stop, given a mylar combiner; probably less with float glass, but that'll give multi-surface reflections.

- You fire light into the edge of a filter (which is what a Varicon seems to do). This is a lot more physically compact, especially if you want to cover wide lenses, but imposes a certain minimum loss in resolution since the filter is intrinsically going to be slightly diffuse.

Which do we prefer? Must say I prefer the reflector approach.

Phil
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#8 Michael Nash

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Posted 13 August 2007 - 09:20 PM

I have been shooting in the low budget Horror genre and I was wondering about pushing some colour into the shadows using something like flashing but in HD.

So I was just wondering if anyone had tried flashing of any sort just to see if it was a tool we are overlooking.


Keep in mind that optical flashing starts at the absolute black signal level (what would be D-min in film) and works its way up the luminance range as you use stronger (brighter) flashing. This is akin to raising the master black or master pedestal in the camera, then the "black stretch" area as you get brighter with the flash.

If you want solid looking blacks in the final image, you'd just have to pull down the pedestal/setup back to zero, undoing the visual effect of the flash. Perhaps it might change the "contour" of the shadow curve without noise, but I don't see where it would really be a benefit over raising the pedestal in camera (since that doesn't add noise like adding gain or black stretch does).

If you just want to tint the blacks in HD for an effect like colored flashing, it's easy to do in-camera or post by raising the pedestal of the RGB channels the appropriate amount. If you want to extend the effect to higher luminances use the black stretch of the appropriate RGB channels. Or create a custom curves in post. Either way (in-camera or in post) rasing the pedestal generally doesn't add any noise to the signal. Boosting signal above that (in the shadows) does add noise, though.

Just a thought; since optical flashing is really just layering a solid but transparent "color" over the image, couldn't you achieve the same effect -- without added signal noise -- by just layering a solid color over your image in post, and setting the opacity wherever you like? Maybe not straight "opacity," but some kind of mix...
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#9 Phil Rhodes

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Posted 13 August 2007 - 09:51 PM

Hi,

I think the difference is that the optical effect is capable of recovering detail from areas of the picture which would otherwise by unacceptably noisy, which is impossible electronically. Whether one would find that the lost highlight range was precisely commensurate, and you could get the same effect simply by opening the iris, remains to be seen. Since CCDs aren't (anything like) linear, I suspect it wouldn't be quite that easy.

This may be wishful thinking, but it comes out of the discovery, while writing for Showreel, that many of these little HDV cameras (such as the JVC range) would actually have quite decent dynamic range if they had another 3dB SNR. All of them saw ten, even eleven stops - but the bottom three were buried in the noisefloor.

Whether flashing would change anything, I think the situation is too complex to predict.

Phil
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#10 gregory mandry

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Posted 15 August 2007 - 12:41 PM

I'm planning for a shoot that is in pre production at the moment. should go to shoot over the next year. i'll try and by some experimenting time when (if) it comes close to shoot. see if i can attach a varricon to the camera.

If i've got an HDV camera handy I may be able to strap that on as well see what happens...
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