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What is the Point of Using Colored Filters When Shooting Neg. Film?


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#1 K Borowski

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Posted 03 December 2006 - 05:13 PM

I read an aweful lot about the use of tobacco filters, warming filters, CC filters, and the like to correct for the color balance of neg films. I can understand filtering when shooting tungsten film in daylight or vice versa, but slight color changes, coming from a still-photography background, are totally foreign to me when working with negative film. With the great latitute of negative film, doesn't it make just as much sense having the prints timed warm or cold? There are obviously physical things done with filters, like pro-mist fillters, or starlight filters that cannot be done without digital manipulation, but I'd think the color corrective filters would be a wash when compared to what can be done in telecine or timing. Can anyone tell me the advantages, if any, to doing this in camera instead of just writing a note on the roll of film saing "time 10CC red"?

Regards,

~Karl Borowski
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#2 freddie bonfanti

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Posted 03 December 2006 - 06:44 PM

Personally i make that choice after a few tests. i try the filters i want to use and shoot a few seconds with each one, then i shoot clean and once i see the results i make my choice.
There are different way of approach, some people believe that filtration is obsolete and rather shoot clean to gain all the information and create a proper look in post, others may not have that priviledge or time or just simply cant go to the lab and try to get it on camera.

hope this helps

Freddie

Edited by freddie bonfanti, 03 December 2006 - 06:46 PM.

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#3 David Mullen ASC

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Posted 03 December 2006 - 08:09 PM

Lab people, especially colorists, aren't necessarily saavy regarding camera filters -- I was talking to another DP who found it was next to useless to tell a colorist to make it "two stops brighter" if they don't have a photography background. A print timer might know what "30CC Magenta" looks like, but not necessarily a colorist in a telecine suite.

It's better to talk to them creatively as to what you want, warmer, for example, and whether the warmth is yellowish, or reddish, etc. You could say "make it look like a Tobacco filter" but the truth is that even I can only make an educated guess as to the exact tonality of a Tobacco versus an Antique Suede, etc. And some of these filters don't even match manufacturer to manufacturer -- Corals, for example.

I generally get warm dailies by shooting a grey scale under a blue-ish light or with a blue-ish filter on the camera, then shooting the scene normally, so that the resulting scene has a warm bias. Later I plan on getting the exact shade when I color-correct -- for now, all I need are dailies that have the general level of warmth I want.

But I can understand the appeal of using a camera filter if it gives you the exact color shade you want, in which case you'd shoot the grey scale unfiltered and then drop it in for the scene.

And some colors are hard to find exactly in timing, especially print timing (as opposed to digital color-correction) which is why odd filters like Chocolate can come in handy, since "brown" is a tricky shade to figure out in post. But as for pale warming filters, I've pretty much given up on them except occasionally when I want a quick way of creating a warmer shot in the middle of the roll. It's just extra glass on the lens and it's too easy for the dailies timer to eliminate it anyway, so I might as well just let him add the warmth himself.
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#4 Stephen Murphy

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Posted 04 December 2006 - 05:38 AM

For me using a coloured filter is like underpainting a tonal wash on a painting. The colour bias informs other colours in the scene, and even if you time most of the filter out i still feel the difference in the shadows. Its a powerfull tool which can be used in an unsubtle or subtle way and personally i prefer to have control over that rather then defering it to a colourist.
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#5 Thomas Worth

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Posted 04 December 2006 - 05:41 AM

The problem with throwing away the filters and fixing all color shifts in post is that your color channels effectively end up being different speeds. For example, take tungsten film. The cyan layer is already a "faster" layer than the magenta or yellow, so you will always have increased grain in the blue channel after transfer (and this is exposing normally). The same type of result will occur when shooting under the wrong lighting. Since you've exposed for 18% gray, your "reddish" or "blueish" footage (for example) now has two underexposed layers. This will show as increased grain in those channels during color correction. If you had used a filter instead of shooting uncorrected, you would have been forced to increase exposure to compensate for the filter, giving all three channels an appropriate amount of light and avoiding the issue of underexposed channels later.
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#6 Fran Kuhn

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Posted 04 December 2006 - 02:04 PM

The problem with throwing away the filters and fixing all color shifts in post is that your color channels effectively end up being different speeds.



Thomas,

I took a cinematography class at UCLA with Mark Woods a few years ago. Mark is a very tech-savvy DP and he explained that using filters is actually quite important if you are interested in rendering an image with all the information recorded the way the film's designers intended. I forget Mark's exact explanation, but it reminds me of what you posted--something like the various color layers being thrown out of synch if the color of light isn't close to the proper temperature the film was designed to record. He didn't rule out departures from this for artistic reasons or when filtration can cause problems with flare or otherwise degrading the image, but he said that many people incorrectly assume that you'll get the exact same result by altering the image in telecine.

Not long after that class I worked with a young DP on a commercial shoot who told me he hadn't used a CC or conversion filter in over five years. Since I work a lot in still photography (where you live or die based on the proper exposure and color of the film) I told him I thought we'd be better off filtering. As a test, we did a shot in open shade using an 81EF, then the same setup with no filter. After correction in telecine, the filtered shot did look noticeably better to everyone, and the colorist said it actually makes his job a lot easier if film is filtered properly. Personally, I would not miss a once-in-a-lifetime shot while trying to get a filter into the slot, but I've had good luck using a color meter and filters to keep the color within the range the film is designed for.

I'd be interested to hear what Mr. Case or Mr. Pytlak have to say (or Mark Woods, if you're out there reading this).
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#7 Dominic Case

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Posted 04 December 2006 - 09:37 PM

I'd be interested to hear what Mr. Case or Mr. Pytlak have to say

Fran & Thomas have more or less got it right. If you make a correction on telecine or in printing, you are selecting a different part of the response curve of the particular colour that you are filtering. So in effect, if you want a yellow look, and you shoot normally (so that, in printing, a 30-30-30 print was neutrally balanced) you would need to print at -say - 27 27 37 - to get theyellowish look that you want. That is the same as saying that the blue-senstiive layer (the one you are printing at 37) is more than a stop overexposed compared with the other two layers.

Secondly, as several people have commented, it's better to have a negative that can be printed normally so that you, as cinematographer, have control over what you end up with.

Thirdly, putting - say - a blue filter over the lens affects the entire tonal range equally - extreme whites are affected as are deep shadows. A simple printing correction that affects mid-tones by the same amount will have virtually no effect on whites in the print. A simple telecine correction will produce a different result as well - though it's possible to combine a number of primary corrections to come close to the effect of a filter on the camera.

But finally, many filters don't just alter the balance of red, green and blue in an overall manner, but cut certain frequencies within the range of one or more of those colours. This has a different effect from correcting in post, which can't be replicated in any way at all - even by digital grading, let alone in printing. Colour enhancers are an obvious example of this, cutting a wavelength range between reds and greens (for example) but leaving other reds and greens unaffected. Many filters work this way.

So there are some looks that only a camera filter can give you, and there are some looks that are more easily obtained in post. For the rest, and especially for minor corrections, there probably isn't a lot of point in agonising over how you do it. For mself, I can't see any point in NOT filtering the camera lens just for the sake of doing it later, unless you don't really know what you are doing and want to put off making a decision till later.
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#8 Michael Nash

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Posted 04 December 2006 - 11:16 PM

I learned the importance of color bias and color correction the hard way on one of my first film commercials, for a carpet store. We were pressed for time on a couple shots so I used the overhead cool white fluorescents to light the majority of the store. One of the carpet samples was a pale cyan color, and in telecine when we corrected out the color of the fluorescents, the carpet went completely gray. :(

I use color filters in combination with digital correction (I don't shoot much for print), mainly to control saturation and bias in the color channels, not just for an overall tint. Digital color correction can be very powerful, but you also run into limitations with compression and whatnot. I've found that a combination of both optical (filters or lighting) and digital corrections give a more organic look, and the most control over color.
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#9 David Mullen ASC

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Posted 05 December 2006 - 03:32 AM

After having my pale Corals, 212's, and whatnot disappear in dailies or the first answer print, only to have to reconstruct the tint in answer printing all over again (ME TO TIMER: "no, a little more yellow in that orange") I realized I was just putting extra glass in front of the lens, which in itself is always a problem if you don't really need to because you increase the chances of flares and double reflections. So I gave up on using pale color filters when it was so easily removed by the colorist / timer and so easily added by them.

But I agree that stronger colors probably should be done with optical filtering because otherwise you are starting to imbalance the printer lights, RGB levels, whatnot, to more uneven levels.

I have a general rule which is to avoid ever using more than two pieces of glass together in front of the lens. So if one of those filters is going to be diffusion, because that's a certain look I'm trying to get, and perhaps the other is going to be the occasional Pola or ND grad, etc. then I don't want to get into the habit of adding some pale color filter for the majority of my scenes, because I may need to occasionally stack the color filter, the diffusion, and a third filter.

However, if it is a movie where I'm not using any diffusion, it is easier for me to feel comfortable with making that filter tray dedicated to a color filter.
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