The process of trichrome photography is not new. In fact, it appears to be the original way photographers created color photos when black and white film was the only option.
So, as our technology has advanced, the need for this process has evaporated, but being an analog photographer means one of my favorite pastimes is recovering the processes we no longer have “need” for.
What is Trichromatic Photography?
Trichromatic photography is the process of taking three identical black and white photos, each taken with a different color filter (red, green, and blue), and then combining the three photos to create a color image.
Originally, the photographer would take the three b&w photos – one through a red filter, one through a green filter, and one through a blue filter, and then use a projector to project the images through the corresponding filter.
But now we have the convenience of combining the images with just a few clicks right in Photoshop. This modern take on an old process is what I’ll be covering today.
Why Would You Try Trichromatic Photography?
Because we do have access to color photography, why in the world would you want to take on this very fussy process?
Well, because it’s fun and oddly satisfying to get a color image from three black and white images.
I was also chatting with Jennifer Stamps, film photographer and another writer for SIWF, about this, and she remarked that it’s also useful for people who only develop black and white. It’s their chance to create some color images without having to bother with C-41 chemicals.
And two reasons is about two more reasons than I usually have for experimenting, so that feels like winning.
Choose a subject. Beware that the process will take a few seconds. You will need your subject to stay still while you take three separate images and put on three different filters.
If the subject is moving, the final image will have a separation of colors in the area with movement.
Set up your camera on the tripod, ideally with a remote trigger, but this isn’t super necessary, it’s just nice to have.
Metering for Trichromatic Images
You will be taking each of the three images with a different filter, so you will have to meter separately for each image to account for the different filters.
I meter using my internal reflective meter, so I will point the camera into something middle grey, and then put my camera in position on the tripod.
You can also meter for each filter by placing the filter over the lens and metering to see how much you’d need to increase exposure for any given filter. You really only need to do this once to determine how many stops to overexpose for each filter.
If you use a handheld meter that has a bulb in feature, simply place the filter over the meter and take your light reading.
This is actually what I did, and I only did it the one time. I found that the blue and green filters needed about 2 stops of overexposure, and the red filter needed about 3.5 stops of overexposure.
So once I found my initial reading, I knew to overexpose accordingly.
Keeping Track of Your Images
You will want to remember the order you shoot your filters, so you can place each image into the corresponding color channel later in Photoshop.
To keep my life easy, I shot alphabetically (blue, green, red). I also found this helpful for exposing, since blue and green need the same overexposure (+2) and red needs 1.5 stop more (+3.5).
I kept my aperture the same and just moved my shutter speed accordingly. So if the initial reading gave me a shutter speed of 1000, I would use a shutter speed of 250 for the green and blue filter and 80 for the red filter.
Because I was working with flash gels, I would simply place the gel in front of my lens (as flush as possible) and take each photo.
Develop and scan normally, but take note of the order of the scans. My film ends up scanning backwards, so I know the order of the filters switches to red, then green, then blue.
Editing in Photoshop
Next, I bring everything into Photoshop. Here’s a video walkthrough of the Photoshop process I use to create a color image from the three black and white images.
Step 1: Open All 3 Images in Photoshop
You’ll want all three b&w images in the same Photoshop file. (Video timestamp: 0:10-1:05)
First, open all of the images in Photoshop. Then, drag the images into the same file so each image is a separate layer.
It can be very helpful to rename the image files with the color filter you used for that image, and then in Photoshop, rename the layers with that filter color as well. Just helps keep everything organized!
Then, I locate the layer with the red image and place the image with the green filter on top of that and the image with the blue filter on top of that. Not that this order matters, but to maintain my sanity, I always do it this same way.
You just don’t want to put the wrong image into the wrong channel (which we’ll cover in a later step).
Your bottom image will be locked as the background, so I go ahead and unlock that so it acts as a normal layer.
Step 2: Auto-Align the Images
Next, I auto-align the images. Most likely the images will not be exactly aligned, and this is a quick way to get them perfectly overlapping. (Video timestamp: 1:05-1:43)
Select all three layers, click Edit in the top toolbar, select Auto-Align Layers, leave all of the settings as-is (Auto is selected under Projection and neither lens correction option is selected), and click OK.
I have found times where the auto-align feature in Photoshop is NOT a useful tool, so I go rogue and just make each layer less opaque and move the layers to align manually.
Auto-align gets super confused if a subject has moved (like a cloud), and sometimes we’re just smarter than technology.
The last step is to place the corresponding image into the channel that matches the filter. (Video timestamp: 1:43-2:25)
This is where I started to struggle. I found a different way to do this for every tutorial I read up on, and none of them seemed to work.
Not sure if it was because of the varying versions of Photoshop, or what, but it took me quite a while to find a way that worked for me.
Finally, I figured out a super easy way to change the color channel for each b&w image, so I hope it works for you, too.
What we need is the the image shot with the blue filter to go into the blue channel, etc. To do this, right click on the layer in the layers panel, then choose Blending Options.
Under the Advanced Blending heading you’ll see R, G, and B checked. Uncheck the two channels that don’t apply to the given layer, so if you want an image in the red channel, uncheck the G and B so that only the R is selected.
Repeat this process for all the layers, and voila! You’ll be left with an image in full color. It’s as easy as that!
I tried this process primarily with 35mm film, and the noise gets to be a bit much when combining the three photos.
If you just want to mess around and get a feel for it, go for some 35mm. If you want a cleaner look, bust out that medium format
I’ve only tried cheapo flash gels just to give trichromatic photography a whirl. I’d be curious how the quality would be affected by actual filters.
I’d love to try my hand at this with actual people. Okay, I did try it with my middle son and neighbor boy, but holding still is an acquired skill, and though they did well, there was still quite a bit of movement.
Will I do this again? Yes. Probably not often, but it is fun to mix it up and experiment in this way. It’s fussier than my usual experiments, but slowing myself down isn’t necessarily a bad thing.
I hope you give it a go, too! Let me know if there’s any way I can help or questions I can try to answer!