Recent three colour process images

Three colour process, separation negatives shot on Ilford Delta 100 with Zodel Baldalux,
colour RGB image composited in Photoshop CS2

In my post last year, 'An Experiment with Three Colour Photography', I described the technique of using three black and white photographs to produce a colour image. For that experiment I used large format film, which meant the taking of each separate shot was inherently slowed down by the process of shooting sheet film. I also had problems when scanning the negatives to create the colour image, as I had to scan each in two halves, leaving problems with both alignment and balancing the colours in the three RGB channels. I subsequently took the tri-colour filter set with me to St Petersburg last September, but only used them for one medium format shot. By necessity this was hand held, and not much quicker than shooting large format, with the problem of holding the camera and the gelatin filters in front of the lens and then pressing the shutter button with two hands (while a stiff breeze threatened to blow the filters into the Neva river). Despite the results needing a good deal of cropping as each shot was not very well aligned through being hand-held, the very distinctive qualities of the three colour technique made me wish I had used it for a few more shots on this journey.

Hand held three colour process, separation negatives shot on HP5 Plus
with Zodel Baldalux, colour RGB image composited in Photoshop CS2

For the above image, a tripod would have ensured a better alignment of each colour. Using roll film rather than large format means that each shot can be taken with quicker succession, although I was still using a manual camera which required cocking the shutter and advancing the film using the red window between each shot. Anything moving in front of the camera shows the time taken between each frame, such as the figures and waves in the shot above, and the clouds. Recent good weather has provided the opportunity to take some more three-colour images. I had hoped for some cloud-free days, as these are the one aspect of the landscape shots which highlight the brief time discrepancy between each shot, but entirely cloudless days are rare. The image at the top of this post was the best of the recent shots; the photograph immediately below shows some problems with shooting into the sun with the filters held in front of the lens causing reflections. The tri-colour filters I have been using are unmounted squares of gelatin, which have the tendancy to pick up fingerprints very easily, and are difficult to clean and this particularly shows up when the sun hits the filter surfaces, and a slight soft-focus effect results.

Three colour process, separation negatives shot on Ilford Delta 100
with Zodel Baldalux, colour RGB image composited in Photoshop CS2

Three colour process, separation negatives shot on Ilford Delta 100
with Agfa Record I, colour RGB image composited in Photoshop CS2

Three colour process, separation negatives shot on Ilford Delta 100
with Agfa Record I, colour RGB image composited in Photoshop CS2

As the 6x9 format gives eight images on a roll of 120 film, this meant that I could shoot two sets of three colour separations, with two frames left on the film. On some of the films I used these frames to shoot second versions of some colours, but I also tried a two colour separation, shooting just through the red and green filters. When making the RGB composite I used the green filtered negative in both Green and Blue channels, essentially giving a red/cyan colour image. This effect was intended to mimic the two colour bipack systems used in the early part of the twentieth century for colour motion pictures (see the Wikipedia article on Bipack Colour).

Two colour process, separation negatives shot on Ilford Delta 100
with Zodel Baldalux, colour RGB image composited in Photoshop CS2

An Experiment with Three Colour Photography

The principles of colour photography are almost as old as photography itself, a three colour process being described by James Clerk Maxwell in 1855, and first demonstrated by Thomas Sutton under Maxwell's direction in 1861. James Clerk Maxwell's method was simple: using black and white emulsion, make three separate exposures with red, green and blue filters. The three photographs were then combined through an additive colour process, by projecting lantern slides of each photograph through the same red, green and blue filters, aligning the projections to create a colour image. This process became more successful when panchromatic emulsions, able to represent the whole spectrum of visible light, emerged around 1900. The most celebrated proponent of this technique was Sergey Prokudin-Gorsky, who documented the Russian Empire before the First World War. The three colour technique was superseded when a convenient, consumer-level colour photography was developed by a number of manufacturers, notably Kodak, during the 1930s with integral tripack colour films.

However, there has been renewed interest in the three-colour process in recent years, in part due to digitisation which makes for easy display of the images so produced. There's a large group on Flickr using the technique, commonly dubbed 'trichromy'. For my first attempt at this technique, I decided to take the approach of making it more difficult than it needed to be by using large format. With taking three separate exposures, I was aware that movement between the images would create ghosting: it would have been quicker to shoot three images in succession on rollfilm, and to shoot more of them, but the challenge of working with large format appealed to me.

Kodak Tri-Colour Filters

To take the photographs, I used my MPP Micro Technical Mk VI camera with Fomapan 400; I had a number of filters which came with a large format lens I'd bought, including a tri-colour set. I took three shots with the RGB filters, using the unsophisticated method of simply holding these over the lens (I took the blue image twice, as I was concerned that the first shot wasn't sufficiently shaded from the oblique sunlight; I also shot it on a glass plate for good measure). The negatives were developed in Rodinal diluted 1:50, for 11mins at 20ºC.

Red, green and blue exposures

Scanning the large format negatives was complicated by not having a scanner capable of taking 4x5 sheet film: I had to scan each negative in two halves. To begin with, I attempted to stitch the two halves of each negative together, and then combine them, but this led to problems with registration across the image, so instead I composited the top and bottom halves of the image separately, then stitched these together. To make the colour image, I used Photoshop to combine the three separate grayscale images by pasting each into a separate channel of a new file in multichannel mode, stacking the channels in the order of red-green-blue, then changing this image mode to RGB.

Uncropped RGB Composite

Despite taking all four exposures as rapidly as possible, I did realise that the movement of clouds in the sky would cause ghosting in the image; what I hadn't expected was how apparent the movement of the shadows is. With the three colour process,  movement between each exposure causes these ghosting effects, making it more appropriate for using with still subjects. Cameras were designed around this problem, initially with backs that could expose three plates in quick succession, followed by dedicated colour separation cameras, which used beam splitters to expose all three plates at same time, such as the Bermpohl Naturfarben Kamera.

RGB Composite

Rather than adjusting the colours in RGB, I made adjustments in each channel separately, feeling that this was more appropriate to the enterprise. The image as a whole suffers from being scanned in sections, leading to the colour being patchy and uneven, yet it works. As I've shot the image in large format, it's possible to look at some details at 100% of the 1200 dpi scan. In the detail of the houses which have reproduced well, the shadows of the trees show colour fringing, which could be due to the movement of the sun, but on reflection it's more likely to be wind in the trees. In the second detail below, looking across allotments to the recycling centre, the arm of a JCB is visible in three different positions, in three different colours.

Detail of houses in the upper left

Detail of JCB movement

Sources/further reading
Wikipedia entry on Colour Photography
James Clerk Maxwell and colour analysis on Wikipedia
Sergey Prokudin-Gorsky in the Library of Congress
Three-Color Camera on Camera-Wiki