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Problems with color through black and white


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#1 Brian Rose

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Posted 04 October 2006 - 10:25 PM

All,
I am experimenting with creating color using black and white film, akin to technicolor. I plan to do really simple stuff, mounting a camera, pointed at a stationary object, and film three times, once through the three primaries, then combine in post. I've done some preliminary tests with digital, in which I set the camera to record in black and white, and then I recorded through the three filters. In Adobe Premiere Pro, I recombined the images and achieved color, but the overall image is very dark. Should I be overexposing when I capture the image? Any idea why my pictures are so dark?
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#2 Brian Rose

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Posted 04 October 2006 - 10:37 PM

I forgot to mention, do I need to worry about infrared light with film? I know digital can be more sensitive, so you might need a hot mirror filter, but would I need a hot mirror for 16mm as well?
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#3 Alessandro Machi

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Posted 04 October 2006 - 11:11 PM

All,
I am experimenting with creating color using black and white film, akin to technicolor. I plan to do really simple stuff, mounting a camera, pointed at a stationary object, and film three times, once through the three primaries, then combine in post. I've done some preliminary tests with digital, in which I set the camera to record in black and white, and then I recorded through the three filters. In Adobe Premiere Pro, I recombined the images and achieved color, but the overall image is very dark. Should I be overexposing when I capture the image? Any idea why my pictures are so dark?


You'll probably get a better answer than the one I'll provide, but here goes anyways. Your filters are giving you pure color with no luminence to hang onto. I suggest reducing the colors to percentages. Instead of 100% yellow, use 30% yellow, and so on down the line.
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#4 David W Scott

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Posted 05 October 2006 - 09:17 AM

All,
I am experimenting with creating color using black and white film, akin to technicolor. I plan to do really simple stuff, mounting a camera, pointed at a stationary object, and film three times, once through the three primaries, then combine in post. I've done some preliminary tests with digital, in which I set the camera to record in black and white, and then I recorded through the three filters. In Adobe Premiere Pro, I recombined the images and achieved color, but the overall image is very dark. Should I be overexposing when I capture the image? Any idea why my pictures are so dark?



I may be being too simplistic here, but did you account for the filter factor on each exposure?
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#5 Mike Rizos

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Posted 05 October 2006 - 07:09 PM

I suggest adjusting your exposure so each of the three filter colors provides 33.33% of the exposure. You need to calculate this, as not all three filters have the same filter factor.
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#6 Dominic Case

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Posted 05 October 2006 - 11:24 PM

Colour filters are far from perfect. For example, a green filter absorbs all the red and all the blue light, but a fair amount of green as well. You need to compensate for that in your exposure.

Different coloured filters have different factors, because they absorb different amounts of the colour they are supposed to transmit. So you need to allow in full for each filter factor when making your exposures. What filters are you using?
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#7 Dominic Case

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Posted 06 October 2006 - 12:16 AM

I found the answer to my question in another thread you started, Brian - about filter factors . . . and I'm cheating by replicating my answer here, as I don't know how to cross-link the two threads to one.

Anyway, the filters are Wrattens 24 (Red) , 47 (Blue), 61(Green).

Incidentally, the 25 is the better tricolor filter, but there isn't much difference between it and the 24.

In daylight (D65), the 24 transmits 17% luminance, The 47 transmits 2.6% luminance, and the 61 is 20% luminance - according to Kodak's filter manual.

However, those take ino account the contribution to total luminance, rather than the simple proportion of light.

The normal photographic factor of a 24 is x8, a 47 is x6, and a 61 is x12

These factors would correct a single exposure of a neutral greyscale back to a normal density.

When you combine the images (are you doing this in Photoshop?), you need to take 33% of each image (or different proportions, haven't thought that one through yet, but they need to ad up to 100%.
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#8 David Venhaus

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Posted 06 October 2006 - 01:04 AM

Major studios often make color separation copies (one copy for each color) on black and white film of color movies for extended storage archival purposes. When new prints are struck from these, they need to do 3 passes for each print, one for each primary color. I don't know the technical details of this but if you can find it, it may be of some use to your project.
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#9 Brian Rose

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Posted 06 October 2006 - 08:54 AM

My apologies for the confusing threads, but I was trying to keep questions short and simple. I had figured if someone asked, I'd give the filter information. Anyways, actually, I'm doing this in premiere pro, since they are video clips (of static scenes) shot through three filters. I may try Final Cut next.
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#10 Mike Rizos

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Posted 11 October 2006 - 09:10 PM

Hi Brian,
Sorry I posted the inaccurate filter factors on the other thread.

I would try something like this with a still camera:
Suppose your shot meters 1/125 at f16. Take your shutter speed and divide it by the filter factor. This will give you your actual shooting speed. The f-stop should remain throughout. So, with Wratten 24 expose at 1/15sec. With Wratten 47 expose at 1/21sec. With Wratten 61 expose at 1/10 sec.

Please keep us posted on your progress..
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#11 Bruce Greene

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Posted 11 October 2006 - 09:35 PM

Hi Brian,
Sorry I posted the inaccurate filter factors on the other thread.

I would try something like this with a still camera:
Suppose your shot meters 1/125 at f16. Take your shutter speed and divide it by the filter factor. This will give you your actual shooting speed. The f-stop should remain throughout. So, with Wratten 24 expose at 1/15sec. With Wratten 47 expose at 1/21sec. With Wratten 61 expose at 1/10 sec.

Please keep us posted on your progress..


This may sound stupid, but...

when you shoot color with a 3 chip video camera, each b&w chip is exposed through a red, green, or blue filter. When the camera is white balanced, the luminance of Red=Green=Blue.

I don't think you can increase the quality by placing additional filtration over the camera lens. You are essentially double filtering each chip.

That said, you might get more interesting results if you shoot b&w film in three passes and have it telecined in b&w and apply the color in post. Or 3 passes of a b&w video camera, but I haven't seen one in a few years. :blink:
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#12 Brian Rose

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Posted 11 October 2006 - 09:37 PM

Thanks for the info. I shot a couple of test rolls that I will send to the lab in the next day or two. Once I get them back, I'll post some frames from the work. Until then...
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#13 Bruce Greene

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Posted 11 October 2006 - 11:57 PM

This may sound stupid, but...

when you shoot color with a 3 chip video camera, each b&w chip is exposed through a red, green, or blue filter. When the camera is white balanced, the luminance of Red=Green=Blue.

I don't think you can increase the quality by placing additional filtration over the camera lens. You are essentially double filtering each chip.

That said, you might get more interesting results if you shoot b&w film in three passes and have it telecined in b&w and apply the color in post. Or 3 passes of a b&w video camera, but I haven't seen one in a few years. :blink:



OOPS, Just re-read your original post. You are shooting film, so disregard my post above. I confused "video clip" with the idea that you were shooting video. Never mind. ;)
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#14 Nick G Smith

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Posted 12 October 2006 - 03:37 AM

This may not be of help to you but I think it is possible to do a similar process on a NLE.

Many years ago I made a number of 3 colour films from b/w neg on a 16mm Debrie contact step printer.

If I remember right I would make up a high con matte on 553 stock for each colour pass. The matte would be placed behind the neg and control the area of colour pos stock to be exposed. The pos stock was then rewound and exposed for each colour.

Colour control was using a subtractive process and I remember doing a lot of testing to get the right colour.

I used to really like the way the colours would 'bleed' into each other, and would start printing different passes one of two frames out of sync to make the joins imperfect.
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