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How-to's

Trichromy

Jon Nadelberg (jnadelberg)


Keywords: trichromy, jnadelberg

Humans are trichromats.  That means we see in three basic colors: red, green, and blue (RGB). These are the additive primary colors.  Our brain knits these three colors together to create all the different colors we see.  Trichromy is the three-color process used in photography that generates the colors that our eyes can see.

Some history. The first photograph was taken in 1827. In the 1860s the first color images were created. In 1935, Kodak invented Kodachrome.  Kodachrome had three layers of emulsion coated on a single base, each layer recording one of the three additive primaries.  Kodachrome was fundamentally three black and white films that had color dyes added to them in processing. During processing the black and white imagery was also removed.  When all layers were properly aligned and viewed together, you saw color. 

Image created by using "Trichromy", combining three B&W images into one color image.
Nikon F100 using Kodak Tri-X Pan 400 film.
Click for an enlargement

 

While Kodachrome is unfortunately no longer made nor processed, the basic idea is still valid and usable.  By creating three black and white images, one for each primary color, and then combining them, we can make color imagery out of black and white film.

In this article, we’ll be taking black and white photos using a faithful old Nikon F100, some color separation filters, and combined with Photoshop we will create color with trichromy.

To generate a color image from black and white film, we need to create three separate images that each contains only the color information for one of the three primaries.  This is accomplished through the use of color separation filters.  These filters are designed to block out most of the other two colors, while letting in the color for the filter itself.  For RGB, we need red, green, and blue filters.

The set of filters I am using is a red #25A, a green #58, and a blue #47B.  You will see this set listed in some places as the filters to use, and are very easy to locate.  Looking online, you might see other filters mentioned.  For example, you might see a red #29, a green #61, or a blue #47.  That will work as well, but while the blue and red filters are easily found, the green #61 is not and you will have to special order it. You might also see a mix and match of these six, or a couple of other ones thrown in as possibilities as well.  I picked the #25A, #58, and #47B for three basic reasons:

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3 comments

Ronald Whitney (CaptRonaldo) on September 5, 2017

Very interesting article Jon. While i am strictly a digital guy, its great learning new tricks. Ron

Jon Nadelberg (jnadelberg) on September 4, 2017

Ribbon awarded for his multiple contributions to the Articles section

In Photoshop, if you place a color image in a color channel, the color gets stripped from it. So, if you take three images, and don't use color separation filters with them when you create the three channels, you'll end up with a black and white final image. If you take a black and white image, and apply a Photoshop photo filter to it, it will not properly set the colors for each channel, and you'll not get correct coloration. The filters are specifically color separation filters. Now, if you took three color images, and then separated out the channels from each of the color images, then combined the red channel from the first, green channel from the second, and blue channel from the third into one new image, it would probably work. But I have not done that. I think the filters are a bit easier, but if you don't have them, this is worth trying.

Geoff Baylis (GBaylis) on September 3, 2017

Donor Ribbon awarded for his support to the Fundraising Campaign 2014 Donor Ribbon awarded for his very generous support to the Fundraising Campaign 2015 Awarded for his generous and continuous sharing of his high level skills with the Nikonians community Writer Ribbon awarded for his contributions to the Nikonians Articles. Ribbon awarded for his generous support to the Fundraising Campaign 2017 Ribbon awarded for his win at the Best of Nikonians 2107 Annual Photo Contest Winner of the Best of Nikonians Images 2018 Annual Photo Contest

Thanks Jon, that's a very interesting project and has improved my knowledge of b&b film use and processing - I switched to almost exclusively colour when I got my first SLR camera. Presumably I can 'cheat' with a DSLR to get the misalignment effects by taking three colour images then combining just one colour channel from each into a new image? I shall do some experimentation this week. Geoff

G