How to Use CTO and CTB Gels to Change the Color of Your Background

One way to spice up your photography is to add gels to your lights so you can produce colorful and edgy looking imagery. Adding wild colors to your photos can offer a lot of creativity but gels can also be used in a much more subtle fashion to slightly alter the color of your background and sky. In today's video I want to share two simple techniques I use to help make my backgrounds on location look more interesting.

As I mentioned above, many photographers use intense color gels on their strobes to produce images that are futuristic or even dreamy. The image below taken from our photography tutorial with Clay Cook shows just how far you can push the creative boundaries by using strong gels on your lights. For this sort of effect, you really want to use "party gels" in order to give your photos the most pop. However, sometimes you can use more traditional gel colors to make a much more subtle effect when shooting out on location. 

Using "party gels" to create extreme color shifts

Color Temperature Blue Gels

The first gel I want to talk about is color temperature blue. This gel, shortened to CTB, is primarily used to cool down warm incandescent lights so they appear closer to white light which reads around 5000k. They can be placed direct over or around your light source to help cool the color or warm hot lights. My favorite brand of gels are those made by Rosco and I prefer the #3204 1/2 CTB gel for most occasions. 

The way I often use these gels is not as described above where I'm gelling warm lights and trying to cool them down, but rather I like to add cooling gels to my strobe light and then adjust my white balance to make my gelled light look white. Essentially what I am doing is bumping my camera's white balance up from 5000k to something around 7000k - 10000k so that my gelled light looks closer to white light than blue light. In a controlled studio environment, this effect might not have much use but when you are shooting out on location with natural ambient light hitting your scene, it will have dramatic effect on the color of your background.

Camera White Balance 5000k, no gel on flash

In this first photo above you can see how everything looks with a standard white balance set to 5000K. The couple is positioned in the shade, the sun is setting to camera left, and my Profoto B1 with beauty dish is lighting them from the front. As you can see, the strobe light looks pretty white (maybe even a bit cool in color) and my background is very blue because of the shaded light in the park. 

In the second photo below, I have tried to warm the background up by bumping my white balance up to 10,000K in camera. As you can see, the background looks much more inviting, warm, and overall pleasing but since the strobe is designed to produce daylight color light at 5000K, the 10,000K setting on my camera makes the strobe light look entirely too warm. The couple's skin tone is now neon orange and unflattering. Obviously we need to do something different if we want our photo to look balanced in color.

Camera White Balance 10,000k, no gel on flash

In order to balance out this scene and keep the background warm, clearly we need to lower the temperature of the flash. By adding 1/2 CTB gel to the flash (or even a full stop of CTB), we can make the flash appear blue which will look more natural. The photo below shows what the gelled flash looks like on our couple when the white balance is set back to 5000K as it was in the first very photo above. You can clearly see our background is still blue like the original but our couple is blue as well.  

Camera White Balance 5000, flash gelled 1/2 CTB

The final step we need to take here is simply to adjust our white balance back up around 10,000K so that both our ambient light in the park and the blue gelled strobe light are warm again. The resulting photo will give our couple nice warm light without it being neon orange and our background will remain warm too.

Camera White Balance 10,000K, Flash gelled 1/2 CTB

As you can see, this photo looks a little more inviting than the first photo where the background is blue because of the setting sun. Typically I try to avoid shooting in shaded areas that has a strong blue cast but every now and then it's completely unavoidable. Having a few CTB gels in your bag can be a life saver when you need to fake a warm, sunny day when you might have an overcast day or the sun has already set. 

Color Temperature Orange Gels

Another technique we can use out on location is using color temperature orange gels on our flash so that we can cool our background while still maintaining fairly white light on our subjects. This trick is basically the opposite method that we just used in the park. Instead of adding a blue gel to our flash, we can add a warm CTO gel which will allow us to lower our camera's white balance and dramatically cool down our background. Below is a photo taken without a gel and the white balance was set to a standard 5000K. The gel used for this demo is the Rosco #3408 RoscoSun 1/2 CTO Gel

Camera White Balance 5000, no gel on flash

By adding a single CTO gel to our flash we can make our day light balanced flash appear to be an incandescent colored light with a much warmer tone. The image below shows how orange the flash has become when the camera's white balance remains set at 5000K.

Camera White Balance 5000, CTO gel added to flash

Unlike the example in the park where we had to increase the white balance to achieve a more normal looking color, when using a CTO gel you need to lower the white balance to something around 2500K - 3300K. This will give our subjects a nice white color light that looks more natural but it will force our sky and ambient light to go extremely blue. 

Camera White Balance 3100k, flash gelled with CTO

As you can see in this photo above, the sky has much more color, all of the blues are much darker and richer, but the color on our couple looks natural. Obviously we lose some of the warm highlights on the ocean which are kind of nice in the original photo but we gain a lot of dramatic color in the sky. 

White Balance 2600, CTO Gel on Flash - Photo by Lee Morris

This technique is extremely useful when you have clear skies like we had in this example because sometimes the color during sunset isn't as vibrant with clear weather as it might be with nice clouds in the atmosphere. You can also use this technique indoors if you want to make your exterior windows appear very blue but you want your subject to still appear to be lit with white light. If you browse through a lot of corporate and medical stock photos online, you will see this technique used a lot. Keep in mind, you can use different gel strengths to make this effect more or less subtle and you can also shoot at different times of day which will also have a drastic effect on the color in your background.

Log in or register to post comments

4 Comments

Dave McDermott's picture

Great video Patrick. I've never used gels in that way before. I will have to give it a try.

Gabrielle Colton's picture

They're really fun to work with, there are so many different effects you can make with them. I use that colored plasticy tissue paper from party city lol

Thanks for posting a detailed-enough article so that I don’t have to watch a video. (Don't like videos) I’ve been wanting to experiment with flashes and gels and this is a good tip.

Emma Grigoryan's picture

Patrick, this is so cool! You explained all in such an easy manner, now I am gonna experiment with geling the location!