Creating colour images from B&W using primary colour filters

[Patrick]

For quite some time, Ive been intrigued by the Technicolour motion picture process. More recently, I was blown away by those 100+ year colour images of the Russian empire which was the result of a similar photographic concept. In particular, I like how the kinds of colours that are produced by such a process are unique and certainly different to the results that one would obtain from conventional colour film.

I would actually like to try this myself and hope to reproduce those surreal vintage looking colours that I see in the old Russian photographs. The shooting should be fairly straight forward. Expose three photographs of a static subject on black and white negative film. One image will be exposed using a red filter, another will be exposed using a green filter and the other will make use of a blue filter. Any movement in the scene will get a strange rainbow colour effect.

I'm not completely sure about the post processing of the scanned images though. With my crude (lack of) Adobe Photoshop skills, should I colour the red filter image red, the green filter image green etc and then combine all three? Is that all that would be required to create a full colour image? Basically, whatever was done with the scanning of those old Russian glass plates is what I want to do with my film negatives to get the same end result.

[Patrick]

I think the main obstacle I'll face is registration issues as the film is wound on after every shot.

[MovieStuff]

I've done this many times and used to use three slide projectors as a demonstration. The easiest way is to pick a blue, red and green filter (lighting gels will work, actually) and then use black and white film to shoot three different frames; one with each color. Do not change the exposure between the three or that will affect your final color balance. Process the three images into black and white positive transparencies and then load them into three slide projectors with the corresponding filter over each. Overlap the images and you will get perfect color. The funny thing is that the specific choice of red, blue or green is not that critical as long as you use the very same filters when you project the image. It works quite wonderfully and is fun to do. You definitely get the Technicolor look.

Good luck!

Roger

[Scotness]

Here's a few links you'll like Patrick:

http://www.flickr.com/groups/prokudin-gorskii/

http://www.loc.gov/exhibits/empire/making.html

http://www.gridenko.com/pg//



Scot

[Patrick]

I've done this many times and used to use three slide projectors as a demonstration.

Projecting them would be quite something and I'm sure those colours will really pop. Well, I do have two slide projectors....all I'd need is a third.

Do not change the exposure between the three or that will affect your final color balance.

That's something that Ive been curious about because don't red filters reduce light considerably more so than filters of other colours? Most colour filters like blue etc only require about half a stop compensation but I'm under the impression that red filters need at least a stop or more. Is that correct?

[Patrick]

Scott, in that second link, it's interesting that when the three images are first combined, the colours look horrible initially, and adjustment is required to get them looking good. Whereas if the positive transparencies are projected with the filters in place over the lenses, the colours are apparently fine straight off. It's a pity that the digital route is not straight forward like that.

Which makes me wonder if i would be a good idea to scan the camera filters or photograph them digitally against a white sheet of paper (manually white balanced of course.) I would then have a set of digitised files of the filters which I could add to the scanned negatives. Though I guess digital cameras and scanners would have their own colour biases so that may defeat the whole point of the exercise.

[MovieStuff]

I've done this many times and used to use three slide projectors as a demonstration.

Projecting them would be quite something and I'm sure those colours will really pop. Well, I do have two slide projectors....all I'd need is a third.

And one of these!

http://cgi.ebay.com/Chief-Stacker-3-goo ... 1e53ba9fe5

Do not change the exposure between the three or that will affect your final color balance.

That's something that Ive been curious about because don't red filters reduce light considerably more so than filters of other colours? Most colour filters like blue etc only require about half a stop compensation but I'm under the impression that red filters need at least a stop or more. Is that correct?

Compensation is required if you are going for an exposure that is lighter than what the filter will normally produce. But, in this case, you are depending on the filter to block a certain amount of light. The best way is to take a reading with each filter and then average the three exposures to come up with one exposure. For instance, if one filter is 1 stop higher, the other 1 stop lower and one in the middle, then use the middle exposure. But use that exposure for all three. If you increase the exposure or decrease it, then you are adding or removing that primary color for that filter and changing the color balance. You can also bracket and choose the combination later that produces best color but, again, it is remarkably forgiving.

Roger

[Patrick]

The best way is to take a reading with each filter and then average the three exposures to come up with one exposure. For instance, if one filter is 1 stop higher, the other 1 stop lower and one in the middle, then use the middle exposure. But use that exposure for all three.

Ive got a feeling that the green and blue filters may each require the same exposure compensation - about half a stop. If I recall, my Hoya no.25 red filter indicated about a stop or a stop and a half exposure compensation the last time I took a reading through it. So I guess I could settle on a one stop compensation from a non-filtered reading as a compromise for all three. In addition to this, when testing and shooting with all three filters, you reckon it's still a good idea to lower the iso setting on the light meter about half stop or one stop for tighter grain with the neg film? My instincts are still telling me not to have any underexposed negative frames with the undesirable weak blacks and increased grain....

And one of these!

http://cgi.ebay.com/Chief-Stacker-3-goo ... 1e53ba9fe5

Ah what every serious technicolour projectionist needs....where would I be without one!

[Patrick]

After some research, it looks like the filter factor for the 25A red filter is 3 stops. There are some differences of opinion on the exposure compensation for the green and blue filters but it looks like green could be 1 and a half stops or maybe 2 stops, and blue - about 1 stop or so....possibly slightly more if I chose a medium blue filter. It looks like the thing to do is to set the exposure for the green filter (the middle) but that would underexpose the red filter image. As mentioned above, I'm tempted to add a bit of overexposure to compensate though in doing so, this would really be exposing for the red filter. Would that have an adverse effect on the colour balance?

Ive been looking at someone's tri-colour work of astrophotography. Some really nice images of the solar system. Interestingly, this guy uses different exposure times for the different filters. Using conventional colour film with his 'Schmidt camera', he said that the results were not entirely satisfactory. Though with the 'primitive' tri-colour approach, he managed to get improved colour saturation and contrast. Though there are still some image problems due to environmental factors.

Some examples of tri-colour astrophotography

http://www.astrofoto.ca/john/tricolour.htm

http://www.scienceandart.com/0gallery.htm

[MovieStuff]

.... It looks like the thing to do is to set the exposure for the green filter (the middle) but that would underexpose the red filter image.....

You are getting side tracked about this whole under/over exposure thing, Patrick. The point isn't to create three black and white images that look like they are properly exposed. Some of the three may look totally black or totally white.

For instance, let's say that you had a red ball on a green table cloth. If you put a green filter over the camera, then the red ball will go black and the green table cloth will go white on the final black and white shot. If you put a red filter over the camera, then the ball will go white and the table cloth will go black. This is normal. Now, if you project those two black and white slides on top of each other with the same red and green filters, then you will get a red ball on a green table cloth.

However, if you compensated for the density of the filters, then it won't work. If you put the green filter on but increase the exposure so that the red ball no longer went black, then you start to change the density of the black ball. Not only does that make the ball lighter, which will let green light through during projection, but you are also over exposing all the areas that are green and making them lose highlight detail. Likewise, if you increase the exposure on the red filter, then the ball will over expose and lose shadowing while the table cloth becomes grey instead of black and that, too, will allow red light to contaminate the green table cloth.

So, unlike normal black and white photography, you aren't creating a black and white image for final viewing as a black and white image. You are creating color separations; each of which will be a black and white image that, by themselves, may not look correct but, together, will each add their own part of the color equation. If you try to "fix" things during each exposure, then you change the equation and contaminate the color. It would be like creating a different exposure on each CCD of a 3CCD video camera. Under normal operation, they all get the same exposure from the same lens during the time of capturing the image. You MUST use the same exposure for all three black and white shots to get correct color balance.

Roger

[Patrick]

Roger, thankyou for making this so much clearer. My understanding of this topic has certainly increased. Okay, I won't 'adjust' the individual exposures during shooting. However, when it comes to the digitisation of the negatives, I won't be the one who will be doing the scanning. It will likely be a local lab that will scan the negatives. Now, with scanning of 'underexposed' and 'overexposed' negatives, the lab employee will more than likely try to 'adjust' the brightness of the images, destroying what I am trying to achieve. I guess I could just tell them beforehand not to 'correct' the images and leave them as they are. They're usually not too bad at following specific instructions.

[Patrick]

Oh another thing. It seems that with green filters in particular, I have quite a few choices. Browsing around, I see samples of light green, medium green and dark green filters on offer. Although interestingly enough, the exact choice of colour is not critical as you say, do you think the medium green or dark green would give better results or would that be down to personal preference? Regardless, I think I'd forget the pale light green.

Hmmm....I wonder if the increased contrast and tonal seperation produced by the use of dark coloured filters would lead to more intense colours and overall more 'pop' in the final tri-colour image. And it is intense colours that I am after!

[Patrick]

One of my first attempts...shot on Ilford FP4 B&W negative film.

http://imageshack.us/f/571/ruinsincolour2.jpg/