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bleach bypass for color desaturation


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#1 Camila Freitas

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Posted 14 February 2006 - 11:50 PM

Hi

I have a shoot in a few weeks and I have a few doubts about how to expose a negative for a skip-bleach print. My main objective with the process is color desaturation and more opaque blacks, though I don't want to have much too contrast since the film is mostly about solitude in everyday life dullness, and the scenes happen in a common family apartment and a supermarket and mostly day exteriors, which I don't think that match a very contrasty and heavy look.

My first question is: since my blacks and midtones are going to go down about 2/3 ou 1stop because of the bleach bypass, I thought about compensating for that with an overexposure of 2/3, so that when the print is processed with the skipbleach the blacks and midtones don't lose as much detail as they would naturally after the silver retention. In order not to wash out my highlights, I would hold them up to +2.5 stops, and my shadows wouldn't be darker than - 3 stops in relation to an 18% gray card.

Well, having in mind that the bleach bypass process on the print will affect mostly the darker areas of the image, it makes sense for me that overexposing 2/3 is advisable to keep some detail in the darker areas. But, if the lighter areas are not to be much affected or not affected at all by the silver retention, it means that if I overexpose the negative by 2/3, they may wash out a little. Can you tell me to what extent are highlights affected by bleach bypass when it's done to the print?

I once read an answer of Mr. Mullen for a student at this forum about a similar question in which he said that compensating wouldn't be necessary in such a case because you could do it on the print. But, to compensate for loss detail with stronger lights on the print will also cause the highlights to go up maybe more than they should, won't it? Wouldn't it be really best to keep your highlights up to a set limit, like +2.5, so that they don't wash out, and overexpose it to have a thicker negative in the highlights and in the shadows so that more detail can "survive" the silver that will be retained?

You see, I have a contradiction here. If you can, help me out by telling me your views on the matter.

Also, since I don't want a too contrasty look, I've been thinking of using a low contrast filter too. In Cinematography (by Malkiewikz and Mullen), it says that these filters sometimes require exposure compensation for less light, since it scatters light all over the negative and has a similar effect to flashing it. If using a filter can be a form of compensating for that detail loss in the dark areas, thus if you use it you wouldn't need to overexpose?
Is there a factor table for these filters (we unfortunately won't be able to shoot tests for this short movie)? Which grade would you recommend in this case? Do the low contrast filters soften the image or produce any artifacts? I'm shooting Super-16, so I don't want to lose much sharpness as well.

Well, I also appreciate if can you send me links to pages where I can find more information about these topics.
Thank you for reading this long and maybe too confused mail!

Camila
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#2 David Mullen ASC

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Posted 15 February 2006 - 12:00 AM

If you are doing the bleach bypass to the PRINT, you don't need to overexpose the negative in order to hold more shadow detail because that isn't going to help, unless you leave the image overexposed-looking. Once you print down to normal brightness, you don't have extra shadow detail visible in the print. If anything, you may have even MORE contrast and deeper blacks because you'd be using higher printer lights to compensate for the denser negative.

A DENSER negative isn't going to improve shadow detail in the bleach bypassed print -- a LOWER CONTRAST negative will.

Hence why people who are using skip-bleach printing to lower color saturation -- not create a high-contrast image -- use contrast-lowering techniques like flashing, pull-processing, smoke, low-con filters, low-con color negative stock, etc. It doesn't really matter if that causes some loss of blacks because the silver left in the print will restore the blacks. It's like you need to lift up the blacks and the shadows on the negative to counteract the crushing of the blacks in the print (to use video terms.)

It would only make sense to overexpose for more shadow detail IF you then pull-processed to reduce density back to normal and thus get less contrast on the negative.
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#3 Dominic Case

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Posted 15 February 2006 - 02:52 AM

Bleach bypass ing the print will increase contrast in the shadow areas. A lighter print will bring the shadow areas a bit lighter so that you can actually see the detail in that increased contrast.

However, overexposing the negative would move the shadows up from the toe of the negative into a steeper part of the curve - that is, increase shadow contrast. This would result in greater difference between the blacks and the midtones, and effectively bury the shadow detail that you want, back into deep black in the bleach-bypassed print.

If you want to avoid burning out the highlights, then as you suggest, controlling the contrast in your subject is the best way. With normal exposure for midtones.

Since increased shadow contrast in the print is the enemy, you could do anything that will reduce shadow contrast in the negative. A moderate flashing of the negative will do just that - it actually extends the shadow response so that you effectively see a little further into the shadows, by flattening the curve. It will lighten the shadow areas in the print, without affecting the mid-tones - and the bleach bypass will put the blacks back to being black.

You can choose between pre or post flashing the neg stock - in camera or at the lab - or Panaflash or similar devices - or low contrast filters, which simply scatter a bit of highlight light over the rest of the image. I think they tend to soften edges a bit more than proper flashing, but others have probably more experience with the filters.

I think I've just said what David said.
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#4 Camila Freitas

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Posted 16 February 2006 - 12:18 AM

I really appeciate your answers! And I still have a few questions about filters for a bleach-bypassed print:

I'm shooting S16 to optically blow it up to 35mm, so I already have a definition loss along the process. This is something that worries me about using a filter all the time, though I know the skip-bleach will also restore a sensation of better definition on the print. I'd choose to use a Tiffen Ultra Contrast - because it seems to be the only Tiffen filter which doesn't produce any halation or extra flare at highlights at all - but it certainly wouldn't be advisable to use the same filter gradation for all situations, would it? We have exterior and interior days and nights, that is, too many different lighting contexts, and for each I think the filter will react in a different way. To be sure of that, of course it would've been great to have had them all tested, but like I told you before, we couldn't make it.

So, could you tell me something about your experience with those filters? At Tiffen website, they say Ultra Cons will let you "see more"... does that actually mean that you have to give the negative less light to compesate for that light gain? How do I measure that... is a spot meter in the place of the lens be enough to measure that? Maybe you can tell me if other filters are best for some of these specific situations.

The other question I'd like to pose to you is about my working latitude when exposing a negative for a bleach-bypassed print; can I work just the same as if I weren't doing it? Or do I really have to hold my blacks and shadows up to -3, as I suggested before? If I have them below that, will I actually be in danger of losing all detail because of the skip bleach, or can't we exactly say the bleach bypass would "darken" my blacks?
Also, would you say that it's best to hold the highlights up to some limit or is that the limit of my negative's latitude and that's all? (I'm using Kodak - Vision 2 250D and 500T, which of course have great latitude, esp. when it comes to highlights).

Thank you once more!
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#5 David Mullen ASC

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Posted 16 February 2006 - 01:05 AM

You can rate the stocks the way you normally would. The main thing is that you need to compensate for the loss of shadow detail in the print. So this can mean using more fill light in general. It can mean using low-con neg stocks. It can mean using flashing or low-con filters of some sort, or smoke.

Yes, UltraCons don't lower definition much at all. They do vary in effect depending on the amount of light in the frame and hitting the glass (so the same filter will look less strong in a high-contrast low-light night scene than a bright day exterior shot.)

Like with using smoke or fill light, it's something you just have to judge by eye. You may decide on an UltraCon #3 in most cases for a semi-flashed look, but when it looks too foggy in the viewfinder because of a bright window in the shot, you may just drop back to a lighter grade. Remember that most of the filter effect will disappear once you use the skip-bleach print process, so some mismatching will be buried by the blacks of the print. Hence if you under flash, fog, etc. all you get in the skip-bleach print is more contrast and deeper blacks, but if you over flash, fog, etc. then your blacks will still look lifted in the print.

Tiffen's Smoque filter is interesting, like an UltraCon but with a dimensional quality like smoke.

You really need to shoot some basic tests to determine the right combination of fill / low-con filtration.

There is also the Arri VariCon device, which fits into a 6x6 mattebox and fogs / flashes the image in front of the lens.
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#6 Dominic Case

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Posted 16 February 2006 - 01:21 AM

Your highlights are pretty safe. Labs usually make the print a little lighter (in printer exposure terms) when it is to be bleach bypassed, enough to offset the effect of the bleach bypass in the mid-tone area. Not sure exactly what your lab will do (this is where a conversation with your lab is ALWAYS the best thing to have) but here we would go down about 3 to 4 trims - that's equivalent to half a stop in the midtones, but rather less at the toe of the curve (of the print). So you can pretty much use all the latitude that the negative offers you at the highlight end.

It's in the shadows that you are monkeying around. The Tiffen claim "lets you see more" means that by adding a bit of light uniformly, the shadows are given a boost to get them past the exposure threshhold of the negative and a little way further up the toe of the curve. (The same additional light has little or no effect in the brighter areas of the image). So a normal print will have slightly lighter shadows: they will have a lower gamma - less difference between each successive gradation of shadow - which means you can get more gradations or steps in before reaching "solid" black. But that is almost exactly the opposite of what the bleach bypass is doing to the print at the shadow end of the print curve (only rather more severely). It is increasing the gamma, so you get to soild black sooner.

So you don't want to overexpose in terms of your mid tones, but it will help you to fill your shadows more than you would otherwise. The Ultracons will help you with that.

David or someone else who actually knows a bit mlore about lighting than I do may be able to put that in to more practical terms.
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#7 Camila Freitas

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Posted 16 February 2006 - 09:35 AM

So, in a general way, I could get a lower grade for exterior/days, a mid one for interior days and nights, and a stronger one for exterior/night, right?

And, if I understand well, if there's anything to be adjusted because of the light boost the filter causes, it can be done at the timing. No exposure adjustments on camera are needed, that's what I want to be sure of.

In Cinematography, you also talk about homemade devices for decreasing contrast and diffusion. Since there's a character in the filme that should be always out of focus, I thought about helping my depth of field by using that glycerin idea smeared on a piece of glass in the area this character will occupy. But, since I'm already using the Ultra Con, and the less glass I put in front of the lens the better, can I smear it directly onto the filter or will it damage it?

Thanks. This conversation has been certainly enlightening for me.
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#8 Camila Freitas

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Posted 16 February 2006 - 09:51 AM

"here we would go down about 3 to 4 trims - that's equivalent to half a stop in the midtones, but rather less at the toe of the curve (of the print)".

I don't quite understand: we would go down with bleach bypass more in the midtones than at the toe of the curve, the darker areas?

"So you can pretty much use all the latitude that the negative offers you at the highlight end".

I gather that the silver retention brings your print down progressively, more at the toe and gradatively less as you go up the curve. At the brighter areas, there should be no silver retained at all, isn't that right? I'd appreciate if you could give me a technical explanation on how that "progression" happens.

All my concern about latitude of a negative that will be printed with such a process is exactly because I know there is a greater "crushing" of the blacks than of the whites, so I'm not quite sure if that negative reating should be parallel for both sides - darker and brighter areas. Besides using a compesating technique such as a filter, should I reduce my working range in the shadows, too (i.e., not trespassing a certain limit for low light, even if I go pretty much to the maximum in the highlights).

I know I'm kind of repeating an earlier question, but that's maybe because I still don't have so clear the physical differences of the silver retention in each area of the curve.
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#9 David Mullen ASC

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Posted 16 February 2006 - 12:47 PM

I think you are overthinking this. Look, on a print, the darker areas have the most density and the brighter areas are the clearest, so obviously when you leave silver in the print, you will be leaving it wherever there is normally dye density, hence why the effect is stronger in the shadows and less so in the highlights.

As Dominic said, since the silver retention print can "feel" dark, there is a tendency to print it slightly on the brighter side, so you may have slightly brighter highlights just to give a good balance with the very deep blacks in the print.

All you really have to worry about is the loss of shadow detail, the increase in contrast in the shadows. Use more fill light and use whatever trick you want to lift up the shadows, knowing that the silver in the print will restore your black levels to some degree. So shoot a slightly "milky" image.

All of your questions could be answered if you shot some tests, which is absolutely imperative if you're going to be this concerned this much about the amount of shadow information lost.

Stop worrying so much about the characteristic curve. All you need to do is shoot some key-to-fill ratio tests and some filter tests, and print them normally and skip-bleach and make a comparison, and then make adjustments to the way you shoot. Don't turn this into an engineering excercise. Are you this picky when you shoot normal footage? Don't you just rely on past experience, some simple tests, and key and fill mainly by eye? This is no different; you just have to compensate for the silver in the print by shooting a flatter image with more shadow detail. How you get that extra shadow detail is up to you.
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#10 Dominic Case

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Posted 16 February 2006 - 09:26 PM

"here we would go down about 3 to 4 trims - that's equivalent to half a stop in the midtones, but rather less at the toe of the curve (of the print)".

I don't quite understand: we would go down with bleach bypass more in the midtones than at the toe of the curve, the darker areas?

Sorry if this wasn't clear.

I was referring to the toe of the print curve - that is the lowest densities, the highlights.
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#11 Camila Freitas

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Posted 16 February 2006 - 10:45 PM

I'm sorry if my questions show some anxiety...
it's only my third short movie, and I got really concerned when I realized I wouldn't be able to roll even simple tests.
But that's it! I'll do the skip bleach even then. Thank you very much!
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#12 Jim Feldspar

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Posted 12 January 2007 - 08:33 PM

You can rate the stocks the way you normally would. The main thing is that you need to compensate for the loss of shadow detail in the print. So this can mean using more fill light in general. It can mean using low-con neg stocks. It can mean using flashing or low-con filters of some sort, or smoke.

Yes, UltraCons don't lower definition much at all. They do vary in effect depending on the amount of light in the frame and hitting the glass (so the same filter will look less strong in a high-contrast low-light night scene than a bright day exterior shot.)

Like with using smoke or fill light, it's something you just have to judge by eye. You may decide on an UltraCon #3 in most cases for a semi-flashed look, but when it looks too foggy in the viewfinder because of a bright window in the shot, you may just drop back to a lighter grade. Remember that most of the filter effect will disappear once you use the skip-bleach print process, so some mismatching will be buried by the blacks of the print. Hence if you under flash, fog, etc. all you get in the skip-bleach print is more contrast and deeper blacks, but if you over flash, fog, etc. then your blacks will still look lifted in the print.

Tiffen's Smoque filter is interesting, like an UltraCon but with a dimensional quality like smoke.

You really need to shoot some basic tests to determine the right combination of fill / low-con filtration.
There is also the Arri VariCon device, which fits into a 6x6 mattebox and fogs / flashes the image in front of the lens.



"The main thing is that you need to compensate for the loss of shadow detail in the print. [/i] So
this can mean using more fill light in general. It can mean using low-con neg stocks. It can mean
using flashing or low-con filters of some sort, or smoke."

How does smoke help compensate for loss of shadow detail? Does lighting the smoke sort of
transfer into lighting the shadow areas? Also, the local rental house here says that it used to
have smoke machines (Rosco Foggers) but not for a while and now users "hazers" which they
explained but I think that I won't really get until I see one in action. When you say smoke,
do you mean the older machines or hazers or something else?


As always, thanks!
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