White Balance Correction
White balance is not just a flash problem. Incandescent and fluorescent lights come in several color versions, and change as they age. Daylight varies too, direct sun, cloudy, shade, sunset, etc. The color is rarely exactly what we expect. When we used color negative film, the photofinisher guy made a good guess at correcting the color, but with digital, this is our job now.
Our digital cameras have white balance settings for daylight or cloudy, or flash or incandescent, etc, so we can change it when we sense the light has changed. One problem though, is these are just one setting, when there are different colors of all of these choices. Auto white balance tries, sometimes good, but it's just a dumb computer, it cannot always get it very close. Our critical pictures will deserve more attention.
For example, even flash tube color temperature varies with flash power level. For speedlights, low power direct flash is bluish, and high power bounce is more reddish. Most studio monolights are the opposite, low power is more red. Sometimes we might not mind a bit of red, for a more warm tone, but of course, too much is a problem. Bounce from beige walls can take on sickly color, but when we get white balance right, the good image jumps out, bright and vibrant.
Some photo editors have a White Balance tool to just click on something white in the image, and the software makes it be white (removing color cast from entire image). In Adobe Elements and Photoshop, this is the middle eyedropper tool (marked red here) in the Levels tool (CTRL L). It works well for minor color shifts, not as well for major shifts. Or Raw software will have its own White Balance tool (works same way, but with much wider range). Select that eyedropper tool (here the middle gray dropper, I marked it in red), then click a spot in image which should have been a neutral color (white or gray), and then the entire image color is adjusted so that spot will become neutral (color cast removed, based on this clicked spot actually being neutral). Preview should be on too (under that red mark), so the image immediately displays the result.
Maybe the picture area naturally has something white in it, a table cloth or napkin or envelope or other paper, or a shirt or a sign or a picket fence or church steeple, then try clicking that. White is common, many pictures include something like this. Can be clouds if not too bright. Colorless objects like overcast sky or foaming water splashes can be good. However random white objects are certainly not guaranteed - if that object's true color was not precisely neutral white (or gray), this can cause another color cast - maybe better, but maybe not perfect. Even if not perfect, you can see the resulting color temperature reported, and can try others around that value a bit. You would like "accurate", but you are looking for "pleasing". Often easy as pie, sometimes not always easy - look for other spots. Try a few clicks around the same spot, to see if one is best. Yes, this may be hit or miss, and yes, certainly we can fault this, explaining how it does not always work, but yes, it can often be just the thing. If your problem picture is some odd color, and there are no other choices, then why not try it? In tough situations, you can be very pleasantly surprised - but just not always. You can always Cancel out, or Undo. You ought to go back to many of your old pictures, and try clicking the WB tool on some white area, just to see how this works.
The Raw White Balance eyedropper tool is much better (wider range), but this Levels eyedropper works pretty well for minor shifts. I tend to say a white object, white seems more common, but it can also be gray, so long as it is actually neutral color - with no color cast in the original itself. Neutral colors are black, gray, and white, those pure tones with equal RGB components (no color cast by definition). Black is RGB (0,0,0) and White is RGB (255,255,255), which are just extremes of gray. Gray is any intermediate tone of equal RGB values, for example (120,120,120). But not every gray object is fully neutral color, blue and pink tints are common, which would not have equal RGB components. Even near black can possibly work here, but there is not much difference possible in channels at value zero. There is much more difference detectable at higher values, say 200, the same percentage of color cast is simply larger numerically and easier detected. An 18% gray card can work fine, but is dark, and has no advantage for this. White is good.
Or much better, in a studio situation, or even walk-about bounce in the same room (specifically, a situation with several pictures with same lighting), a truly great solution is to simply include a known true white card in the first test picture. I use this
Porta Brace White Balance Card. 5x7 inches, $5, plastic, durable, washable, inexpensive, accurate, and it is all we need. There are also several fancy complicated expensive systems, but nothing works better than the white card. You click on the card in the test image to tell the White Balance tool "This spot is neutral - Make it be neutral". Presto! Whatever color cast there is removed, also from the entire image area (which assumes of course that the subject and background have the same lighting). The color of the clicked spot is adjusted to force equal RGB components there, which is neutral. The same color adjustment will also work when transferred to all similar pictures in the same lighting situation. The color white is not all-important, it could be a gray card (best if not too dark), but the important thing is that it be actual neutral color, a white or gray shade with equal RGB components - without color cast.
However, if white is exposed so bright to be clipped at 255, then any tint is clipped away, and there are no detectable differences left (when clipped at 255). This is not likely in any normal exposure of the scene or portrait (can happen in clouds), but keep it in mind. Don't put the white card a lot closer to the flash. The subject holding it near their chest in the test shot is fine.
This Levels tool only works on that one selected image, but at minimum, it shows you what good color looks like, a visual goal which you can then work to imitate in the other pictures. Or instead, if only the other standard photo editor color tools are available, start with the blue-yellow slider - if too blue, then try less blue, etc. Raw software is better, offering more features, real White Balance tools, and for example, is good about copying White Balance to multiple images with one click. Also the Raw White Balance tool adjusts both color temperature (blue to yellow) and tint (green to magenta), whereas I'm not sure this levels eyedropper does. I usually instead use the Adobe Camera Raw (ACR) White Balance tool for this, and select all the images in this same session (under the same lighting), and click this card spot in the test image, and the same White Balance correction is applied to all selected images at once, one click. Again, Presto! Very trivial job, but perfect results. We don't even have to think about White Balance then. It's like magic, simple and easy.
The standard abbreviation used here, ACR is Adobe Camera Raw, the Raw software from Adobe, in Photoshop, Lightroom, and Elements.
FWIW, early white balance methods, like Adobe Auto Levels (the Auto button above), just aligned the right end points of the data in the three channels (very slightly clips ends of each RGB channel individually, and then aligns the right ends of the three), which makes white there. This makes the assumption that there is usually actually something white in the image there, which works fairly often (better results), but it also fails a lot (worse results). Newer White Balance tools click a known neutral spot (manual assistance to identify the right spot), a white or gray spot known to have equal RGB components, and this aligns the channels to make those RGB components actually be equal values at that spot. Very straight-forward, equal RGB values is a neutral color, color cast is removed.
About Correcting White Balance - It's Important
Including a good White Balance card (Porta Brace White Card is about $5) in the first test scene is truly excellent, but several other white things which can occur naturally in the image might do this correction reasonably well, at least better than nothing. Outdoors, a white sign or house or picket fence maybe. Indoors, a shirt or envelope or paper or painted bookcase. Maybe not perfect, sometimes even poor, but often is a big improvement. If you're having problems, and it's there, then consider trying it. If it doesn't work, you can always look for something else, or cancel out.
Clicking the White Balance tool on that white spot says "This known spot is neutral color - make it actually be neutral color", and any color cast is removed.
This white or neutral thing might be many things, maybe a white shirt or collar or table cloth or envelope or sign or church steeple. Something is often present, but it should actually be neutral color (no internal color tint). Not everything is neutral enough to work, so if it instead causes worst white balance, and many things will, then just cancel out, and try something else. I'm not promising everything works, but the actual White Balance card is as good as guaranteed, and faith is a comforting thing. Adding this card to the scene is so easy to prepare for, just set it out there, or have the subject hold it once (the test shot). Certainly in a fixed studio situation, where you spend time setting up the lights and setting their levels, for Pete's Sake, get an accurate $5 White Balance card, and use it in your first setup pictures. You can carry it in your bag, and use it anywhere - just take a test picture with it included in the same lighting. It makes all the difference, especially in obvious problem areas, and why not for the important work too? For bounce flash, one typical card reading probably works everywhere in the same room. You do need a way to transfer this corrected White Balance value to the other multiple images in same lighting situation, but Adobe Raw software makes it trivial (even for JPG), allows correcting dozens of the session images the same way with one click to do all of them. White Balance doesn't have to be a problem.
Another way 1: For JPG images, your camera may have the Custom White Balance feature, where you photograph something known to be all neutral white or gray, either a close up of a white or gray card, or you cover the lens with a white filter, set up at that time in that light. There are a few variations of this you can buy, but it is not that hard. Nikon says to just photograph a neutral white or gray object in the same light (focus is unimportant, just fill the frame with it). No actual photo is made in this mode, but then the camera Auto White Balance corrects that known neutral thing for that light, and this Custom White Balance setting remembers to apply same setting to all subsequent pictures - which of course must be in the same lighting to have any meaning. This is basically the same idea (something known neutral to correct), but I think including a card in the first test shot is maybe better, and certainly easier and more versatile.
Another way 2: The Nikon SB speedlight on the hot shoe offers the CLS Flash Color Information Communication, which reports a color temperature supposedly corresponding to the actual power level used (Canon has this too). If the camera is using Auto White Balance (variable, allowing it to be changed), this mode then becomes an entirely different method than regular Auto White Balance, and if with hot shoe flash, now Auto WB simply uses this reported temperature for White Balance. This is in contrast to Flash White Balance, which is always the specified constant no matter what the power level or color was (and the camera cannot change it if we specify Flash White Balance).
Those sample results can be viewed here. I have mixed emotions, sometimes better than other times. But flashtubes definitely change color with power level. Speedlights become more blue at low power, and most studio monolights become more red at low power.
A look at Raw White Balance
All of our light simply varies in color. Incandescent and fluorescent bulbs are available in a wide range of colors, warm white, cool white, daylight white, etc. Bulbs also shift color a bit as they age. Daylight of course includes direct sun, cloudy, shade, sunset, etc. Even flashes vary color with their power level - that is just how flash tubes work. Almost all studio flash units are more red at low power, and speedlights are more blue at low power. Speedlights never specify a color temperature spec, because their color simply varies with power level. Studio lights shouldn't, but might, which can only apply to some for one unspecified setting, maybe full power, but of course they vary with level too.
Raw files set white balance later, in the Raw software, when you can see it. At right is the Adobe Camera Raw (ACR) white balance menu, which is about the same thing as in cameras. We can choose one standard choice, or we can actually fix the image right. This is what Raw is about, making corrections later after we can see what is actually needed.
D800 with SB-800 hot shoe flash, ISO 200, f/8, 1/250 second. There are only two pictures here, bounce and direct flash (first column), plus copies with different WB processing applied in ACR. The numbers under the images are the WB correction values performed and reported by ACR. A lower K number result is more blue correction of a more red image to be more neutral. There is about 1000K color temperature difference in this same flash at this range between these two power levels. The first row (full flash power) with standard Flash WB shows speedlight full power flash is reddish, and second row with 1/64 power flash is more blue (Full power to Half power is the big change, then it tapers more slowly. And most studio monolights act the opposite, becoming 300K or 400K red at low power).
The first column is Flash WB in camera, and left uncorrected "As Shot" in ACR. The second column simply sets Flash WB in ACR (Which is a proper thing to do in Raw, at minimum). The third column more specifically corrects both using the White background (22x30 inches, artists supplies from the craft store). The fourth column corrects on the accurate $5 Porta Brace White Balance Card. The fifth column corrects on the white cup itself. So both top and bottom images become the same color, neither are tinted, both are neutral colors of neutral subjects, and both are pretty good. The worse your image WB is, the more you will love this method. Humans do sometimes prefer a small pink warmer tint however.
With the White Card, we can click on this spot that we know to be neutral, and the software adjusts the image to remove the color cast there to make it be neutral. Neutral means equal RGB components of the color, no color cast, White or Gray or Black can be neutral (non-colored), but white is the easiest and most useful. The points I hope to have made here are:
- Flashes vary color with power level. Daylight varies color with cloudy or shade conditions, or sunset. Incandescent and fluorescent bulbs come in several colors, and vary individually with age. Correct color is rarely an obvious situation. The two flash power levels above vary with a standard constant correction (not precisely correct for either), but color is more consistent with individual eyedropper corrections.
- If you are having trouble with white balance, often you can simply click the WB eyedropper on some white thing already found in many images, maybe a T-shirt or a white sign or paper or envelope or table cloth or church steeple or picket fence. You may be pleasantly surprised with a pleasing result.
- Or maybe not sometimes - It needs to be a neutral white, and not all white things are neutral enough to work like an official $5 white card made for the purpose. Certainly in any fixed studio situation, you SURELY want to include a white card in the first test shots. A gray card works pretty well too.
Flash tubes are roughly daylight color, but they can't have any actual white balance specification, because their color varies with power level.
The Nikon camera manuals put a footnote on every mention of temperature degrees K, saying "approximate". Color is not linear over a range of degrees K, so the camera is probably working in Mired units anyway (which is linear). The camera was set to Flash WB above, and ACR interprets its "As Shot" value as 5900K (you surely want to set WB in ACR instead). The temperature K number is never reported in the image file - Exif does not show any K number. There is a Nikon Exif value: Color Balance 1 - 1.6875, 1.15234375, 1, 1 (example taken from next image below). These are coordiantes into the RGB profile Nikon assumes, and Nikon and Adobe seem to interpret this number slightly different. You do want to select White Balance in ACR if using ACR (another reason is you can see what you are doing then). The difference is a moot point, even if we had exact numbers, the light is usually some different unknown anyway . White Balance has already been done in JPG filesy, whatever it was, it's done now, but the Raw software is doing it now, so ACR tries to figure something out. But the point is, ACR has a WB menu too - use it. Someone needs to specify a proper WB. :)
Possibly none of the numbers are "correct", the system cannot know about the flash that was used, or the actual light color, but it is clear the $5 Porta Brace White Card easily comes out easiest and best every time (neutral is always neutral). A neutral gray card works too.
Fortunately, we have no use for a precise number right here, we just fix it and forget it. Flash units normally cannot say anything about their own color temperature, because color varies with power level. This picture was also at 1/64 power, and some color shift is expected (red from studio lights, blue from speedlights, if at low power). Anyway, none of this is the issue. No matter what explanation, the only issue is, no matter what, color varies, and we always need to correct whatever color mismatch we discover, to make the result become neutral, or possibly at least our preference of "correct".
ACR has the Select All button which selects all images, or you can just select some of them, but often you can correct many of them at once, with one click. You click the white card in one of them (or click one of the standard WB values, Flash or Cloudy, etc), and this correction is applied to all that are selected, in one click. The white card only has to be in one of them (a test image). This is a really big deal for multiple photos all in the same session lighting, studio or walk-around bounce in the same room.
How White Balance Correction Works
This section is not "how to", it is about "what is WB?", in a practical sense. Next (in 1. below) is another example, Raw straight out of the camera. Nothing is adjusted yet. It is not real bad, but it is a little warm, red (at 5900K). The camera shot it as Flash White Balance, with AlienBees B400 lights (Main light in Large softbox was near 1/8 power level at ISO 200). But it is Raw, so we can simply set White Balance any way we please now. The Raw software provides a drop-down menu to select any regular White Balance value (just like in the camera, shown above). The default was "As Shot" (the value interpreted from camera). In hindsight, it would have been simpler to explain selecting Flash White Balance here, but it often needs a little correction regardless (because Flash WB is one constant value, but flash tubes vary color with power level). The light often just does not quite match the camera setting.
This is a Nikon D300 Raw image in Adobe CS5 Camera Raw software. The only "raw processing" work done was that the Raw file was opened (no edit yet). It could be simply output as a JPG file to look same as here, but so much opportunity exists first.
1.
So White Balance is off a little here (NOT because it says 5900K, but because it is a bit red), but the point is, notice the multiple histogram spikes at the right end of the Red, Green, Blue channels. The large spike is obviously the white card, which is major here (large mass of same one color, more pixels than any other bright color here), easily seen, no mistaking it in the histogram. Neutral color is defined as having equal RGB components, but these now are not equal. Red has higher values than blue here. These spikes are the RGB components of this color of this card... but they are not equal RGB components, which neutral white ought to be. And the card is neutral white, so our goal is clear.
So... next (in 2., to demonstrate a point, that White Balance is actually pretty simple to understand), I played like I was the white balance tool. I merely adjusted first the Temperature, and then the Tint sliders, manually, to line up these right end histogram peaks of these three curves by eye, to place them at more equal location (and make them be white) in the histogram. This is what white is, and it is what White Balance tools do - balances the channels so that actual neutral colors (white or gray) have equal RGB components. It is of course more accurate when we know this peak is actually something neutral, which was true here. It could have been a gray card with the spikes in the middle, but it needs to be known neutral (and for humans, spikes to identify it). The result is properly less red now. My try came out 5400K Temperature, and -20 Tint. These numbers are relative here, not numerically significant in themselves. Adjustment is made either on a pure white object, or just for good results by eye.
2.
Next (in 3. below, to demonstrate the White Balance Tool is very easy to do), I instead just used the regular Raw White Balance tool to simply click the White Balance card (normal routine procedure). The drawn red line below shows selecting the White Balance tool, and where it clicked the white card. It came out 5300K and -18 tint. FWIW, the little red arrow marks a small white space on the dress, and alternately clicking that was very close, about 5350K (but not all white places are this neutral - the zebra stripes up near shoulder were off more, and variable). But there are often opportunities present, and you will likely recognize the correct color when you see it pop out. But it is a real good idea to pay $5 for the card, and know what you have. You gotta see it to appreciate it, but it is real pleasure to see the color pop in correctly, so easily. Remember, this is not even about Raw, we always have to deal with correcting White Balance, but Raw just makes it so easy (wide range, good tools).
The yellow line marks the Color Sampler Tool (not required, nor part of the process, I just wanted to show it). It shows the RGB components of the marked (clicked) spot, both are shown by the yellow line. After the histogram peaks are lined up well by clicking the White Balance tool on the White Card, which adjusted color so that this spot shows R 210, G 210, B 210, which are equal RGB components, i.e., neutral white, no color cast. If it were burnt out bright to 255, 255, 255, it would be worthless then to detect a color cast. Don't overexpose it, but also, don't overexpose your portrait either. So there is not much risk, but a gray card would prevent any risk of that overexposure of the card. 18% is pretty dark, but it works, and there are now newer "digital" gray cards, much lighter for this White Balance purpose. But the white card works great too, so long as it is actually neutral. Since this card of course happened to actually be neutral white (planned that way), then all is good, the RGB components are equal, and the color is now neutral and correct, same as the actual card. The unadjusted first image showed 219, 210, 210, unequal, and slightly red (same as histogram shows). My manual rough try above showed 210, 210, 208... pretty close, and 1% is about the absolute minimum difference human eyes can detect.
3.
Now suppose... what if this picture out of the camera accidentally used incandescent white balance? - Giving it a heavy blue cast, since the promised orange incandescent light was not actually present (created here with 2900K White Balance, same result as if camera did it). It really doesn't matter, since it is Raw, we can still set it any way we wish now. Flash White Balance here and now would have been fairly close, like if the camera had done it - not perfect, but in the ballpark, it was flash after all. But see the three widely spaced channel peaks? That's the color of the supposedly white card. Blue channel is strong, red is weak, not even close to equal. But no problem at all, Raw makes it easy - either just select the Flash White Balance menu to get as close as the camera could have done it, or just click the White Card to be precise.
4.
The point here was to do an extreme correction shift, to show what White Balance correction does. The little animated GIF here shows the histogram as the temperature slider moves up warmer (from 2900K to 5300K), shifting the channels; the blue channel moved down to be lower, darker, and the red channel moved up to be higher, brighter. It is an extreme shift, but Green does not shift as much. The three peaks are the RGB components of the white card (neutral color when equal, no color cast). Clicking the white card would do this more simply, but here, the known white histogram peaks were manually aligned (which does the same thing).
Watch carefully as the Temperature slider moves from 2900K (blue image) to 5300K (neutral), and then the Tint slider moves from -3 to -18 to clean it a bit more. It simply shifts the blue and red channels independently until this white peak has equal channel positions (equal RGB components). It can do this because we know the white card is neutral, and bright, and large to cause the recognizable peaks, and we know white is equal RGB components. The White Balance tools today make the three RGB components of the clicked spot be equal, which is done by shifting the channels. It is the SAME final result as 3. just above it, 5300K and -18 tint.
Histogram height is relative, it simply auto-scales the height to fill the height, and the height jumping around might be confusing until we learn to ignore it. We don't care about a "count", everything is relative. Histograms just always try to fill most of the full height, so we can see it better. As the tones are shifted here, the tall clipped peaks (red at zero, blue at 255) come down, giving space to increase overall height of the rest, so it does, automatically. Absolute height is not important in histograms, it is all relative, and the data is always scaled to try to approach full height. The result white point (exposure) could be moved to slide the data to the right a little, but portrait skin tones are often better if you don't push it so close.
This channel shifting is what White Balance does. This extreme case shown would be a drastic shift for JPG. The camera does this while still 12-bit data, before output to JPG. And Raw software does this while still 12-bit data, before output to JPG. JPG is only 8 bits per RGB channel, however smaller changes can still work OK.
Continued - Why Choose Raw Processing?
