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Screw on filters versus post production manipulation


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#1 David A Smith

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Posted 24 June 2008 - 11:33 AM

I am somewhat new to this but I did go to film school so you can throw info at me and most of it I will understand

I am really baffled in regards to post production altering of an image (color and light) versus "on set" manipulation of an image using warm cards or screw on filters for example. I am referrong to video not film

What I am trying to understand and I may be incorrect

1. When you use warming cards or screw on filters with a camcorder, are you not altering light as it enters the camcorder and the CCD is processing that with digital numbers?

Versus post production where you are altering individual pixels or groups of pixels

Is there not a difference in quality of image?

For example, let's say you use a #1 warm card for white balancing and you like the way it looks, how is this so different than just using a white card to balance and then "warming" up the image in post production editing. Is the overall look better for one versus the other?

Thank you for your time

David
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#2 Dan Goulder

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Posted 24 June 2008 - 11:48 AM

Generallly speaking, anything you can do optically to achieve a desired look during acquisition will give you potentially "cleaner" results than electronically "boosting" certain aspects of the image in post, which can potentially boost undesireable things as well such as noise and artifacts.
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#3 Adrian Sierkowski

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Posted 24 June 2008 - 11:49 AM

Also, for what it's worth, sometimes when applying filters in post, you are adding in more compression (not to mention it taking more time to render) as opposed to doing it on set.
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#4 John Sprung

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Posted 24 June 2008 - 01:15 PM

I am really baffled in regards to post production altering of an image (color and light) versus "on set" manipulation of an image using warm cards or screw on filters for example.

The main difference between hanging filters on the camera and doing it in post is that on the camera you have access to the original real world distribution of energy and wavelengths. In post, you only have the relative amounts of three primaries that are supposed to -- and usually do -- look to our eyes like the light that existed on the set. That's why you can use a "hot mirror" filter to eliminate infrared on set, but there's nothing you can do about it in post. In theory (nobody's done it yet) you could also notch out the 546.1 nanometer mercury spike that makes flourescents turn that nasty green, but there's no way in post to tell what green came from mercury and what didn't. Color wise, most everything else you can do in post.

The one thing to avoid in using color filters on the camera is pushing stuff out of the dynamic range of one of the channels. For instance, if you use an extreme red filter, you could get the red channel clipping or the red layer saturated, and there's no way to undo that in post.

Likewise, you can always add diffusion in post, but there's no legit way to take it out. If you're sure you want to soften the image, on digital cameras it's a good idea to do part of it in camera. Most OLPF's are designed to cheat a little on the Nyquist limit, especially on Bayer sensors, which have a lower limit for red and blue than for green. Adding a little diffusion on camera gets rid of some residual aliasing.

So, bottom line, use filters on the camera to take the color and sharpness in the direction you want to go, but take care not to go too far. You can add more in post, but you can't take it out without some negative side effects.




-- J.S.
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#5 David Mullen ASC

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Posted 24 June 2008 - 01:51 PM

I take a conservative "fifty-fifty" approach in general if I know I have some post manipulation possibilities -- it's not really a halfway approach, but the general idea is to get the look baked into the original but give myself some flexibility to take it a step farther. So night work is not quite as dark as I want it to be in the final, color tints are not quite as strong as I plan on doing later in post, diffusion is one notch lighter than I really like so I have some ability to soften further in post, etc.

I don't really believe in the "shoot it neutral" approach either, for artistic and technical reasons -- I think you have to commit to a look in the original just so everyone on the set and in post gets used to the look, but you have to be smart about it, and responsible, and not go nuts with heavy colors and heavy diffusion, not if it is easy to push it to that final degree in post.

Also, with compressed and color-subsambled video formats, you have limitations in post in terms of how far you can push things before artifacts like noise appear, so there is some argument for getting some of the look in the original and just tweaking it further in post.

Just remember that when you white balance to warm cards, etc. all you are doing is changing the gain in individual RGB channels to shift the color. If it's a small amount of shifting, then it's not much different than doing it in post and it's less of a hassle than pale warming filters, etc.
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#6 Michael Collier

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Posted 24 June 2008 - 03:25 PM

Also keep in mind that when you use white balance to get your look, you risk (or more likely have to work around) other elements.

As an example I shot a scene meant to be very green. Since I wanted practicle christmas tree lights to read green, I balanced the camera through neg-green. Any light I wanted to be white had to have neg green applied to make the look work. The problem comes in when you understand that one (or more) chanels are pushed closer to an upper (or lower) limit.

In that scene we had a DJ light throwing multi-colored rays of light everywhere. The red rays would super-saturate, to the point where they looked fake. Because the green channel had been boosted so much, the saturated reds would over-saturate, since on chip the red channel was almost pushed to the chroma limit. If I had used a neg-green glass filter, that might not have been an issue. we had to be very careful to maintain a propper 'white' exposure and fill with at least a base level of 'green' fill on any element in frame that was to be a bright red, to keep it from taking on the same look (difficult when your working with a fight scene with lots of stage blood.)

for elements you know you have to alter in the digital realm, its best to do a fair amount of that in the white balance (IE, production couldn't afford a neg green glass for that one scene, and I couldn't gel 200 strands of christmas tree lights). Balance happens before it goes to compression, so the signal is still in a 10, 12, or 14 bit uncompressed stream, so radical color shifts at that point amplify the noise less, and since there are no compression or sub-sampling artifacts baked in yet, those are not exagerated in the same way they would be in post, especially if your working in the 8bit 4.2.0 DV color space, or other highly compressed scemes.

but bottom line, if you can get the real glass, and can commit to a direction for a look, its much better. White balance tricks are the next best thing, but far from perfect. Post digital manipulation is best saved for 'final tweeks' and situations where no other practical method is avalible on set.
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#7 Walter Graff

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Posted 24 June 2008 - 08:32 PM

I don't know if I agree with any of the posts here. I'm probably closest in agreement to David's comments. I do a lot of post manipulation from color to actual Tiffen post production filters with the introduction of these remarkable post filters that do exactly the same thing that filters in camera do. I try to create as realistic the look I want in camera but know that sometimes I can not make it perfect or know that I can get help in post. It's a give and take. I try to creat a look in camera but always know post is going ot allow me to finnesse far better and more accurately than looking at a 20 inch monitor in a field or under a tent in December. I did a spot with a guy sitting on motorcycle in front of some soft focus bushes in the background on a sunny day. Looked fine when we shot but in post we thought the trees competed with him so we added graduated NDs in post. Looked no different than it does in camera. Plus we had even more control. Did a Chevy spot in the early spring and thought the colors were a bit muted. So we added sky blue in post, warmed up the dirt in post and tweaked the grays to the point where they worked in post as I didn't have the luxury of time in shooting. Could I have messed with the camera to create these looks? Somewhat but why take your film stock and through off how it sees? Let is see the way it should and take advantage of the same techniques we've been using in film transfer since I was going to sessions. All of these effects are easily done in post and all are completely reversible. Some even fix mistakes in camera such as HMI flicker. I've had to use that filter on occasion. Being old school I never play with colors in a camera much beyond maybe a push of a red or blue gain. We always baseline a camera and then do things outside of the camera with filters, white balance etc but as some have said here, you get in serious trouble if you play with a cameras insides and often can't fix it properly later. One thing I would suggest is to NEVER adjust the green channel since it is what the other two channels use as there reference. Video cameras are designed to be shaded properly and then adjustments made only to certain things, such as only the red and blue channel, and even then not the way today's folks play with cameras from some of the posts I read on various sites. Then again most folks don't even use a vectorscope or wavefrom in post and create finished pieces so far out of spec that colors tear and monitors they watch the stuff on struggle to handle the levels. I think most of what people do to cameras insides is plain wrong. It's one of the reasons why pro cameras have a users menu and a engineering menu. The engineering menus were never designed to be played with but somehow when video was introduced to filmmakers they took it upon themselves to start playing with peds and gammas, etc as if they had a right to even though nine out of then times folks have neither the proper knowledge to do so, nor understand the consequences. Today's post makes even poor white balance non existent. I have a plug in for white balance. Take a scene that was incorrectly or poorly white balanced and hit a button and it's white balanced just like if you did it in camera. The reality is that what I did ten and fifteen years ago in film transfer is no different than what I do with video today. Only thing that is different is attitudes that forgot that all this work we did with film always started with a baseline for how the film sees, and most of what we did was only in camera filtration, exposure/development manipulation and color correction. Today everyone plays with the inside of a camera far too much when all those effects and looks can more easily be done in post with more control and less headache. Perhaps my attitude is different due to my experiences. I have shot a lot of stuff beyond just experimenting and do a heck of a lot of post and simply don't find most stories folks communicate about post 'headaches' as realistic or accurate.
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#8 Dan Goulder

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Posted 24 June 2008 - 09:34 PM

I don't know if I agree with any of the posts here.

We may not agree with yours, either. As one who prefers to avoid filtration most of the time, there are still situations that arise on occasion where one would be limiting the "magic" that can be performed in post without resorting to some degree of in-camera correction, and I don't think it's responsible to advise otherwise. (On the other hand, if your intention is to keep people from over doing it, especially where they end up boxing themselves in, then I would concur with your position.)
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#9 Walter Graff

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Posted 24 June 2008 - 11:33 PM

Yea overdoing it is what I was referring to. Far too many people play far too much inside a camera rather than setting a camera up to see well and use talent to make great pictures. I get at least 5 emails a week from folks with sample footage asking me how to fix it, when it is clear they went far too overboard shooting when they should have found a happy medium and if necessary used post to take it to the place it could have been without the point of no return. Most of the time I tell folks they can't go back after seeing what they did. The current generation is into playing far too much inside the camera for my tastes.
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#10 David A Smith

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Posted 25 June 2008 - 08:17 PM

Thank you for responding everyone, learned quite a bit from the answers

David Smith
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#11 Bob Woodhead

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Posted 25 June 2008 - 08:54 PM

I think a graduated ND filter (glass) would be a good example of when you can't "fix it in post". Maybe those clouds up high are clipping white, and you don't want to iris down, at the expense of losing black detail elsewhere. A polarizer is an even better example. Those are the only two I carry.
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#12 Michael McIntyre

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Posted 28 June 2008 - 03:01 AM

Far too many people play far too much inside a camera rather than setting a camera up to see well and use talent to make great pictures...... The current generation is into playing far too much inside the camera for my tastes.

And you could argue that far too many people are playing around in post. Aren't all creative decisions, by definition, a personal statement? There are things I do in-camera, there are things I do in post. No need to prattle on with these cyclical, long-winded diatribes about nothing.......

I was on this project back in the day and I had this thing that did this thing but other people do other things and they are wrong because I've been doing this so long and on one project there was another guy that said one thing and I said don't say it and then we looked at the scopes and I applied a filter in this one shoot for a corporate client and then I told these kids about how awful their footage was because I get all these tapes because I'm such a professional and I do all these things way before anyone did them and I told a client not to do this one thing but they did it anyway because they didn't seem to understand the play of light during this one filmic moment that reminded me of a dream where I was white balancing with a filter I read about in some software that was inspired by a show cut at this place that used to do the telecine for this one guy I heard about but never met but didn't really want to anyway because I'm much more professional. Did I mention that I was a professional and that I'm thinking of collecting all my infinite wisdom into a collection of let's not say books per se. That's too cliche but some sort of electronic tablature device that can contain both my ego and all of my infinite intellect and this tablet will be able to power my house and my car that cost a lot of money since I've been doing this for so long and I made a lot of money back in the day before any of you were even born. I actually invented the motion picture camera. I made it out of 2 rocks and an amphibian exoskeleton. I fashioned a membrane cell structure that captured light and you flipped the book in our cave and pictures danced on the wall which I measured 2 stops overexposed which reminds of another expensive shoot that I worked on where this guy said he didn't understand using scopes on the set and I demonstrated the basic principles of luminance and chroma and how the interconnectivity of the Grassy Knoll and Kermit the Frog was actually a very real and dangerous collision of physics much like the need for people to stop playing around in-camera.

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#13 Walter Graff

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Posted 28 June 2008 - 06:58 AM

A creative decision in post is to use a cut or dissolve. But what if you could get into the software code and started to change numbers that affected the program but you wouldn't really know which numbers did what. So you tried a few. It made a cool effect with the software. Problem was you couldn't get the software to go back to normal. Even worse you found out that what you did no longer allows the video to play properly on your TV. You never knew you just can't use a bright red bulb as the overexposed red causes the sound to have a buzz. Someone said you need to make sure everything was in spec with the waveform and vectorscope but you've never needed them before so why start now. Far too many people think that playing around in a camera is creativity and a requisite to being a DP. It can be when one understands the controls, their interaction with each other, and the consequences, but not when it substitutes talent and experience which for many it seems to do.

Sort of like these posts here where someone says hey I'm new to this. I got a great camera (it has three chips of CCD). Now my friend says I need to buy a RED camera or this can not be released in theaters. He says it has something to do with resolution. Should I buy one or stick with the Sony camera I bought at BH Photo for $499? It has three chips so is professional. And before I can shoot I need to get a lens adapter, a matt box, light meter, something called a split diopter, and a Dutch tilt-like head. Can someone tell me what the best options are for these devices so I can shoot my movie? I guess it will be in US theaters, but what if it gets picked up overseas? Should I get my talent to sign releases? How do I make it shoot with those cool black bars on top and bottom (postal bars?) I see on TV? Also what is a Dutch head? Do I need to get filters for the matt box? Which ones work for science fiction. I know a split diopter has something to do with shooting, and a lens adapter is something I need or I will not really be shooting 24p. Oh yea, how do you make the camera shoot 24p or does it do that when you put the lens adapter on? I'm really excited about this. I was going to go to film school but think the film will be so great that I'm just going to do it. I've got $100,000 saved up and borrowed from family members so it is going to be great. It better be, it's all the money me and my parents have in the world. Oh yea, one scene involves a guy jumping off a building during rush hour. He lands on a propane truck and causes it to explode. Police panic thinking it's a terrorist attack and come running through the streets. I got some great police uniforms and my friend is a gun collector so he's going to loan me some assault rifles. WITHOUT BULLETS OF COURSE. Do you think I can shoot this on a slow day of the week during real rush hour? My friend knows how to make a really cool explosion with a really orange fire ball. Will I need a permit, or should I just do it for the realistic effect? Maybe I should just do it with a steadycamera. What filter works best for this? All these creative decisions...

PS, I just adjusted something called master pedestal so it's negative 99. I read on the web on a professional site called DVX that you can create some cool effects doing this. There is a guy there who really knows what he is talking about. It makes everything really dark and distorted which I really like (it's a science fiction thriller), but I have to use so much light now or you can't see the picture well and my talent sweats in about 2 minutes because of the intense light so we have to shoot the scenes really fast. We have a big fan to keep them cool but it blows their hair when we shoot and it's kind of loud so they have to talk louder. How can I make the camera see better? I have the gain at hyper 16 but it makes the picture look funny because of all those grains of salt we now see. I'm using auto iris. Any suggestions? And who do I call so I can get this movie out there when it's done. Movie making is hard!
Oh yea, it's taken almost a year but the OFFICIAL website for the movie is up. You can read cast bios, see amazing trailers and look at some cool stills. It's gonna be huge! www.dunselthemovie.nut.

Note: if one don't understand the reality of this post and the implications, hopefully someday you will.
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#14 David Mullen ASC

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Posted 28 June 2008 - 11:37 AM

One reason to be more subtle / conservative with in-camera effects, coloring, and exposure... is that often you don't have optimal monitoring on location compared to a post house, not to mention a lack of scopes and waveforms (or knowledge of how to use them). And generally you aren't dragging around a post house-style 50" HD monitor on location.

It helps to have some experience taking your own footage through post for broadcast so you learn the impact of certain on-set shooting decisions when doing color-correction.
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#15 Daniel Smith

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Posted 28 June 2008 - 01:06 PM

I've been taught both ways... digital manipulation increases noise sure, but optical effects can't be or atleast it is very difficult to reverse them. Entire shoots have had to be re-done because the optical effects were either too strong or un-wanted later down the line.

Depending on the effect I leave most effects to post production. I don't think the increase in noise is as great as people make it out to be, and the versatility of digital manipulation is un-matched.

Edited by Daniel Ashley-Smith, 28 June 2008 - 01:09 PM.

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#16 Michael McIntyre

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Posted 28 June 2008 - 01:14 PM

Note: if one don't understand the reality of this post and the implications, hopefully someday you will.


And therein lies my beef. Ever since you tried to hijack the "look" settings thread (DVX100), there's been a consistent, condescending tone towards the use of in-camera manipulation. You've even gone so far as to suggest certain ops don't even know how to read scopes. To play the Graff hand, I've been finishing for broadcast for over 15 years now. That's innumerable episodes for international deliverables, every day, every week, QC on-the-spot. I'm fully aware of the power of post. I also appreciate the abilities of doing some things in-camera. I don't need convincing otherwise and I don't need these tired, pious posts born from some deep-seeded unhealthy need to be liked and feel important. These strike me as the ramblings of a narcissistic emotional vampire windbag.
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#17 Walter Graff

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Posted 28 June 2008 - 01:28 PM

Too bad I was addressing the board as a whole and no one in particular. Don't take life personally. It's never about you. And neither was anything I said, hence why I did not address you personally by name.

Signed,

the narcissistic windbag
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#18 David Mullen ASC

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Posted 28 June 2008 - 01:35 PM

I've been taught both ways... digital manipulation increases noise sure, but optical effects can't be or atleast it is very difficult to reverse them. Entire shoots have had to be re-done because the optical effects were either too strong or un-wanted later down the line.

Depending on the effect I leave most effects to post production. I don't think the increase in noise is as great as people make it out to be, and the versatility of digital manipulation is un-matched.


The thing about noise is that the visibility is dependent on the size and type of monitor that the image will be viewed on (CRT vs. LCD, for example, or 17" vs. 40"). Noise problems have become a lot more visible now that people are watching things on big LCD's.

And I had some blue noise problems on "The Quiet" that were only visible in the film-out to 35mm -- I didn't catch it on the 50" CRT HDTV monitor that I color-corrected it on.
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#19 Walter Graff

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Posted 28 June 2008 - 01:46 PM

Even worse is how we've taken a step back in overall quality using LCDs and as a result it takes very little noise, color saturation, exposure ratio to see what looks like a problem.
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#20 Daniel Smith

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Posted 28 June 2008 - 04:38 PM

The thing about noise is that the visibility is dependent on the size and type of monitor that the image will be viewed on (CRT vs. LCD, for example, or 17" vs. 40"). Noise problems have become a lot more visible now that people are watching things on big LCD's.

And I had some blue noise problems on "The Quiet" that were only visible in the film-out to 35mm -- I didn't catch it on the 50" CRT HDTV monitor that I color-corrected it on.

This is a good point, the operator who taught me to shoot neutral and grade in post is predominantly a TV camera operator, whereas film is normally displayed on much larger displays making the grain much more evident.
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