HomeDIY Film
Posted in : Featured / Photography Principles on February 17th, 2013.
white_balancing_with_the_histogram

I was going to give this article the title of “How do I use a grey card?“, but grey cards can be used to do more than just correct your white balance, and even with just that there are a couple of different ways to do it, of which this is just one.

When shooting RAW,  the white balance setting isn’t absolutely critical, as you can adjust it in post.  That being said, depending on how you meter your scene (for example, with the histogram), having an incorrect white balance setting can cause your exposure to be off (or at least appear to be off, which makes you overcompensate, creating an incorrect exposure).

Metering with the histogram is not the only way to meter your scene, just one of several ways, but it helps to understand all of the different methods in order to be able to determine which is the most appropriate for any given photograph you wish to create.  Even though understanding how to meter with the histogram may take some time to figure out, ensuring correct while balance will greatly improve your accuracy, and learning how to correct your white balance via the histogram is a great way to get there quickly.

Remember that the histogram for an image, as it is displayed on the back of your camera, is generated based on an in-camera JPG conversion of your RAW file using the image preset settings applied in your camera (including the white balance setting), so, while helpful, it’s still not perfect.  Again, this just gives you another option.

White balancing with the Histogram? Hold on a minute, I thought the histogram was for metering exposure?

Traditionally, yes, that’s what the histogram has been for, however, the histogram has evolved. Most modern DSLRs will actually show four separate histograms instead of just the one you might be used to (RGB histograms may be disabled by default, so be sure to consult your manual if you can’t find it).  It’s this development that we can take advantage of in order to determine a “correct” (neutral) white balance.

If you are using a camera with just a single histogram, it’s showing a combined brightness level for each of the colour channels in your image added together.  It’s like desaturating the image, and just looking at the brightness level of each pixel in the final image.  This can’t really be used to set your white balance.

Individual RGB and Combined Histograms

This is where the four histogram display comes in.  One of the graphs is the combined histogram, the same as the one shown on single histogram view, and the other three are for the individual colour channels in your image; Red, green and blue.

Ok, so how does the histogram help me set the correct white balance?

Well, we know that in order to make a neutral tone appear neutral, the red, green and blue tones all need to be present in equal quantities.  If we take a photograph of a grey card, and each of the three colour channels is not there in equal amounts, we will get a colour shift.  Our goal is to set our white balance in order to counteract that colour shift and show neutral grey as it should.

All our DSLRs come equipped with several preset white balance settings.  Sunny, Cloudy, Flash, Incandescent and Flourescent are pretty common, and you may have a couple of other options.  Some DSLRs will also allow you to dial some slight compensation into each of these presets in order to shift it slightly warmer or cooler to suit your taste.

The problem with these presets is that they tend to vary from camera to camera, even within the same brand.  If I grab Nikon D100, D200, and D300s bodies, set their white balance to “Sunny”, and make identical photographs with each, the RAW files will all record a slightly different colour temperature, and all show a slight shift from the others when viewed side by side.  Bringing any of those images into Adobe Camera RAW or Lightroom and applying the “Sunny” preset in there will, once again, provide a colour shift that’s slightly different from all three images from each of the different cameras.

DSLRs can also offer a couple of other ways to correct your white balance.

  • By creating your own custom white balance preset (some cameras will allow you to save multiple custom presets you can recall at will).
  • By dialling in a Kelvin temperature directly (this is handy if you want to sync up multiple cameras exactly).

Using a custom white balance preset doesn’t require the histogram, although the histogram can tell you if your custom preset is accurate.  This was the method which made me pick a different title for this article.

I have several white balance presets stored on each of my cameras for various lights and modifiers that I regularly shoot under.  Here you can see the saved setting “d-2″ selected.  This is the one I use when I’m just at home shooting snaps in the living room.  Others are for different flash units and different modifiers.

Custom Preset White Balance Settings

This method, though, also has its problems.  Until you can actually get your RAW file on a computer, you don’t know what Kelvin temperature your camera has chosen.  It simply tells you that you were using one of the custom white balance presets.  If you’re just using the one camera, that’s fine.  If you’re trying to sync up multiple cameras, especially when shooting video, this can be a big issue.

This method also doesn’t allow for any compensation, as provided with the built in presets.  You can’t just dial them slightly warmer or cooler than neutral.  They’re always neutral.

So, the one we’re most interested in here is entering the Kelvin temperature directly – which is where the RGB histogram comes in.

If we look at the simplest device used to balance our colour temperature, a neutral grey card of solid density throughout, on a combined histogram display we will see a single spike shooting up somewhere along the histogram.  Theoretically, straight up the middle is good with perfect exposure on an 18% grey card (your in-camera processing settings may shift this up or down depending on your brightness and contrast, even though you are shooting a correct exposure according to your in-camera meter or a handheld light meter).

Accurately Exposed White Balance Card

This shows us that 100% of the brightness in the scene is sitting at the same point in the shot.  But, this doesn’t really tell us whether our white balance is correct or not.  If we look at the set of images below, 111-1 shows the RGB histogram for the above shot.  As you can see, a white balance temperature of 7690K gives us a neutral tone, perfect grey.

Accurately Exposed White Balance Card with the correct temperature settingAccurately Exposed White Balance Card with a warm temperature setting

Image 111-2 shows us how the individual RGB histograms look when the white balance is shifted to 10000K, which appears a little warm.  While the combined histogram is still showing a correctly exposed shot, you can see that the red channel is slightly brighter, and the blue channel is slightly darker, which is what gives that slightly warm appearance.  Given the actual temperature of our light (7690K), this isn’t a massive shift, so the difference in exposure isn’t that great.

In the following two images, you can see what happens when we make an extreme shift, all the way down to 2500K.  In 111-3, you can see the strong blue colour that we’d expect, but that shift has also caused our image to display a darker overall exposure in the combined histogram.

While the exposure has not changed, and shifting the white balance back to 7690K in post would give us the same image as in 111-1, it’s falsely telling us that the image is underexposed.

Accurately Exposed White Balance Card with a cool temperature setting appears underexposed This shot appears to be accurately exposed with a cool temperature setting however it is in fact 2/3rds of a stop underexposed

The final image, 111-4, tells us we have a correct exposure when we open up the aperture 2/3rds of a stop (going from f/11 to f/9).  If, in post, we load up this image, and then shift our white balance to where it should (7690K), the image would actually be 2/3rds of a stop overexposed.  You can also see here, that when we correctly expose for the overall scene using the combined histogram, the blue channel is actually clipping and blowing out.

While that apparently blown out information is still there in the RAW file, which you can get back simply by shifting the white balance, without knowing that your white balance is off, it simply appears that you’ve blown out the blue channel.  You may see this in the middle of a shoot, and then try to underexpose to compensate.  This is where confusion slips in as to whether or not we have the correct exposure when our white balance is off.

We know that neutral grey, of any brightness, is a combination of equal parts red, green and blue.  When we look at the four histogram display, with separate histograms for each of the RGB channels, if the white balance is accurately set, then each of the channels will show a spike in the exact same spot, as in image 111-1.  If they’re not all aligned in the same spot, we know our white balance is either too cool or too warm.

So, even though one of the major advantages of RAW is that I can shift my white balance in post, it’s still a good idea to get it right at the point of shooting too?

This is just something that’s important to me.  You can set your white balance whichever way you prefer, this is just another option and it’s one of several different methods I may use depending on the situation.

I’ll typically use this method when either when shooting video, at events shooting RAW+JPG, or if I’m using multiple cameras simultaneously (for either stills or video).  Dialing in the Kelvin temperature manually gives me colour consistency between the cameras, and all the final images & video footage can be treated identically in post to get the same result.

As mentioned above, and demonstrated in the four images above, having an accurate neutral white balance also means you’ll be able to get a more accurate level of exposure if you’re also metering with the histogram.

So, the goal is to get the colour neutral for every photo?

That might be how this article comes across, but no.  The goal is not necessarily to get your white balance set to a neutral level, but simply to know where that neutral state sits on the Kelvin temperature scale given the lighting situation you’re currently shooting under.

From there we can make creative decisions.  Perhaps it’s a chilly day, and you know in advance you want to cool down that shot a bit to impress some of that coolness on the viewer, or you want to bring some of that incandescent light bulb glow and warmth into your shot.  Go right ahead, but at least you’ll know exactly how far you’ve shifted away from that neutral point in each of your shots, and will be able to meter accordingly.

Sometimes, even having the white balance set to neutral and taking the shot will cause your exposure to be out if you know in advance you want it much warmer or cooler than neutral, and may even cause those colour channels to clip once you adjust the colour temperature in post.

One example of this is shooting portraits.

Now, when I’m photographing people, I do like my skintones slightly warm.  Not orange, sure, but warm.  If I set my white balance to its neutral setting, take a few test shots, and adjust according to what the histogram tells me, when I bring them into Lightroom, and warm them up, I’ve probably blown out the red channel on a lot of the skin.

If I know in advance that I’m going to be warming them up, I can determine my neutral white balance setting, add the amount of warmth that I need (by adjusting the Kelvin temperature in the camera) at the point of capture, and then compensate my exposure accordingly.

For example, in this image, I was using the camera’s “Flash” white balance preset, which makes the lights I was using appear slightly warmer than they actually are.  The shot was actually metered externally with my Sekonic L718 handheld meter.  You can see with the combined histogram that, while perhaps a little on the bright side, the image appears to be good.

A correctly exposed portrait of Collette Von Tora, or so it seems

Once we switch over to the RGB histogram, we see a completely different story.  In the image below, the black pixels overlaying the photograph are actually completely blown out in the red channel.

Our portrait of Collette doesn't appear to be quite so accurate once we inspect individual colour channels

Now, I know my camera and my lights.  I know what this particular white balance setting will do to the preview image, I know what my in-camera image processing settings will do to the preview image, and how both of those will affect the histogram.  I also know that if I meter with my Sekonic I will have to compensate slightly with my exposure settings in order to get things exactly where I want them.

I did this intentionally to demonstrate the point made earlier in the article.  If you don’t know whether your white balance is correct (“correct” being a subjective statement based on how warm or cool you want your final image to be from neutral, if at all), you don’t know if your exposure is correct when metering via the histogram.

In the shot above, my white balance is wrong.  It’s not where I want it to be.  Yes, I want to be slightly warmer than neutral, but not quite as warm as the “Flash” white balance preset gives me with the lights I was using.

If I did not know this (after all the photo on the back of the camera looks “close enough”, right?), I might look at the histogram above, see that the red channel is blown out, and underexpose by maybe a stop or more in order to retain that red channel detail that I perceive to be missing.

If this were the actual white balance setting I wanted to use, this would be the correct thing to do.  As it is not the white balance setting I ultimately want to use, once I shift the white balance to where it should be in Lightroom, my image would actually be underexposed.

This is why I feel that learning to white balance via the histogram is so important.  You can’t just rely on how the image looks on the back of the camera.  Every camera will show the same white balance setting slightly differently.  My wife’s Nikon D3200 shows images to be MUCH cooler than any of my Nikon bodies, and each of my bodies are slightly different from each other too.  The same white balance setting can even appear to be different on the same camera when viewed under different lighting scenarios.

So, even if you know you don’t want to shoot with a neutral white balance, knowing exactly where neutral sits (and knowing how your camera is going to process the image) will allow you to more accurately meter your shot when using the histogram as a reference for metering.