Saturday, May 30, 2009

Temperature of Light - part 6 (How to set an In-Camera Custom White Balance)

Now that we've covered the need for a custom white balance for in-camera jpegs, I thought I would take a stab at showing how to do it. This will apply directly to the Canon 450D, but with a little thought and perhaps consultation with the owner's manual, one should be able to apply the concept to other cameras as well.

What you need
To set a custom white balance you will need a known white surface and of course your camera. Best to use a calibrated white balance system. There are several to choose from ranging from around $10 U.S. and up. I suggest something like the QP Card, Opteka Premium Reference Color & White Balance Card Set, or the Digital Grey Kard.In a pinch, a piece of white paper will do, but try to choose one that appears less bright white because the bright white papers typically use optical brighteners that cause a blue color cast when exposed to ultraviolet light. The brighteners fool the eye into thinking it is a brighter white by adding a tiny blue bias. This works because of the way our eyes interpret color. However, your custom white balance will compensate and make things come out with a bit of a red/yellow cast. Usually this is minimal and so using a piece of paper with optical brighteners is still preferable to using nothing.

Steps for Obtaining a Custom White Balance

  1. Take a picture of the white patch (or white paper) making sure that it covers the center area of the frame. For a Canon 450D, it “should fill the spot metering circle.” (pg 90 of
    the manual).

  2. From the menu system (shown below), select “Custom WB”.

  3. Select the photo of the white patch and then press the “Set” button. The camera will ask if you want to use white balance data from this image for the custom white balance. Press the “Set” button for OK.

  4. The camera then displays a reminder to set the white balance to custom. Oddly enough, though there is plenty of screen space, instead of spelling out the word custom, they simply display the icon for custom white balance.

  5. Press the “WB” button on the back to set the white balance type. Use the right/left arrow keys to select Custom (shown below), then press the set button.

You are now ready to shoot. If the display is active, it should show the custom white balance icon below the ISO setting.

Coming Next
That's it for now. In the next posting I will demonstrate how to set a custom white balance using raw processing software. I will use my favorite, Bibble 4.10, but might also take a stab at it with Canon DPP and Adobe Camera Raw.

Until then...


Continue on to Temperature of Light - part 7 (Custom White Balance with Raw Files)

Monday, May 25, 2009

Temperature of Light - part 5 (In-Camera White Balance Settings)

My purpose in writing this posting, is to convince you to use a custom white balance. If you are using jpeg files from your camera, it is the only way to ensure you get correct color rendering. Some time ago I gave a white balance card to a friend and taught him how to use it with his digicam. A few months later I heard from his daughter about how much his photos have improved since he started using the “thingy” that I gave him. Why is that and why couldn't the camera just get it right? Read on to find out.

What is a Custom White Balance?
A custom white balance calibrates the camera's color rendering to the actual light being used. This works regardless of the light's temperature and it works reliably. For most cameras, you take a picture of a known white or near white surface and then program the camera to calibrate its color rendering to that white.

Why a Custom White Balance?
The short answer is because digital camera auto white balance is very unreliable. Take a look at the above images. All of these were taken under the same incandescent lighting, but using different white balance settings as indicated. The one on the bottom closely matches the actual magazine.

Why not use Auto White Balance?
Auto white balance may seem a simple function, yet few if any cameras get it right much of the time.

Take a look at the photo above. It was taken with incandescent light and the camera was set for auto white balance. This magazine cover has a good B&W print that should have been sufficient for the camera to get a decent color balance. However, as is the case for many cameras (especially Canon DSLRs), the auto white balance fell far short of the mark.

The lower photo shows the camera's display, including the RGB and luminance histograms. Notice how red dominates. The camera has chosen a color temperature that is not even close to incandescent.

Auto white balance attempts to figure out the color temperature of the light being used by searching out the brightest thing in the image. It assumes that this is a white surface and so does a color balance based on that. It sounds good on paper, but in practical use it leaves much to be desired.

The problem lies with not always having a true white reference. What if there is nothing white or even close to white in the scene? In this case the camera makes a best guess at what might be close to white and calibrates to that. In reality it does not usually get it right and sometimes it doesn't even come close. There is also the effect of color shift. Under incandescent light, something with a blueish hue might appear as white to the camera, in which case it will make a bad assumption about color. In the case above I cannot imagine what went wrong, but it certainly is not right.

Why not use Presets?
Presets for daylight and incandescent usually get you close, but quite often, not often not close enough, and sometimes they are just plain wrong. The image above was taken with the incandescent preset. The improvement in color compared to auto white balance is obvious. However, it still has a reddish hue that is not found in the real life subject. The RGB histograms from the camera show the improvement, but also show the lack of proper white balance. Because the magazine cover is essentially black and white, all three histograms should look the same.

If without a way or time to calibrate and under known lighting, I would use a preset rather than trusting auto. However, what if I'm in a room that is lit with Reveal incandescent bulbs? From part 4 of this series we know that the Reveal incandescent bulb will produce a light that has more blue than a standard incandescent bulb. If my camera is set to incandescent white balance, then I will get a blue cast in my images.

Fluorescent bulbs are even more problematic, as they have much variability from based on the manufacturer and type. They also shift color with use. Some cameras have two or more fluorescent settings, but that cannot possibly cover all of the variations one might encounter in the real world. Even if there were a preset, how would you know which one to use? When possible (as it usually is), it is always better to get a custom white balance. Daylight varies by time of day and atmospheric conditions.

What About Using a Custom White Balance?
Glad you asked because if you are going to let the camera generate jpeg files for you, this is the best way to go.
The photo above was taken after performing a custom white balance. As you can see, the image correctly depicts the black & white photograph on the cover of the magazine. A look at the RGB histograms in the next photo down confirms an excellent white balance. The simple step of performing a custom white balance has produced a near perfect rendering of the subject, enough said.

Coming Next
In the next posting I will demonstrate how to set an in-camera custom white balance using a Canon 450D. This tutorial should make a good primer even for non-Canon users, so until then...


Continue on to Temperature of Light - part 6 (How to Set an In-Camera Custom White Balance)

Tuesday, May 19, 2009

Temperature of Light - part 4 (Effects of Color Temperature on Camera Output)

So far in this series we have looked at what color temperature is, how color temperature is determined by spectral content, and the temperatures to expect from some common light sources. This posting gets more practical with a little experiment to show the effect of color temperature on what we get from the camera.

For this experiment, I have made five sets of photos, all with the camera set for daylight color balance. This tells the camera that we are using sunlight, so it adjusts the color balance accordingly. Using the same setting for all of the photos allows us to see the differences between light sources. The setup includes a calibrated color check chart so we can see the effect on color rendering. It also includes a QP Card, which has patches for near black, middle gray, and near white. The white patch gives a good visual representation of the light's color. The middle gray patch will be used for making RGB color balance measurements to assess each light sources color rendering.

Bear in mind that the interpretation of spectral content for sunlight is controlled by the camera manufacturer, Canon. The following images are from in-camera jpeg files. The camera is a Canon 450D. I set the camera's preset to “Faithful”, which sets all of the color and contrast controls to zero.

As you probably already know, the Seattle area has a reputation for having the most consecutive overcast days per year compared to any other state in the union. Few places can claim more cloudy days than us. We have some of the happiest slugs on earth... but I digress. What I meant to say is that by chance, it was a near cloudless day, so I was able to get outside and make the sunlight photo in bright, 11:00 A.M. sun. Sometimes things just work out :-)

Lightsource: Sunlight at 11:00 A.M. on a near cloudless day.The colors in the chart are clearly discernible and the white balance card shows what appear to be neutral white and gray patches with no obvious color cast. Using the color picker to take a measurement on the middle gray patch, I get (96, 97, 99), which is close to a perfectly neutral gray.

Our other clue to good color balance is seen in the Red, Green, and Blue histograms.
The between the Red, Green, and Blue histograms. The three histograms show the same basic distribution of pixels at about the same luminance. This is good enough to use with no additional white-balance adjustment.

Lightsource: 150W Halogen Incandescent light bulb (modeling lamp from a monolight).I didn't have any regular incandescent bulbs on hand, so I used the modeling lamp from one of my studio lights. It is no different from any normal halogen bulb except that it has an additional layer of glass to make it safer (JDD style). The spectral output is virtually the same as for an ordinary incandescent light bulb. They both burn a filament to create light. The only difference is that for one, the filament burns in a vacuum and for the other it burns in halogen gas.

Back to our analysis. Notice that the white balance card shows a distinct reddish tint and the colors in the chart are badly skewed toward red. I don't need to make a measurement to know that the color is off considerably. Nonetheless, using the color picker to take a measurement on the middle gray patch, I get (140, 80, 46), which confirms the red bias that our eyes see. This reddish look is the same that we get when we forget to set the white balance on our digital cameras when taking photos indoors. When this happens, the photographer's phrase for describing this effect is that “it was an artistic choice.”

The Red, Green, and Blue histograms tell the story. The reds are about twice the brightness of the greens and nearly four times the brightness of the blues. The spectral content of this light is not even close to sunlight.

Lightsource: 100W Reveal Incandescent light bulb (special coatings to raise color temperature)I had some “Reveal” incandescent bulbs available, so thought I would take a look to see if “Reveal's unique neodymium glass filters out dull, yellow rays unlike regular soft white bulbs...”

Visually you can see that the although the colors are still substantially skewed, reds do not dominate quite as badly compared to the unfiltered halogen bulb. The histograms indeed show a slight improvement in that the blue is now a bit stronger relative to the green and red. The difference is enough to be notice by the eye, but for photographic purposes, the difference is marginal at best. This light source is still a distant match for daylight and the bulbs still dissipate the majority of the power used as heat.

The gray patch of the white balance card measures (131, 75, 52), which confirms a strong red bias with slightly more blue content compared to the halogen lamp.

Lightsource: 23W Daylight Balanced Compact Fluorescent light bulb
I gave this a 10-minute warm-up period, as these bulbs shift their color temperature dramatically over the first few minutes of being powered on.The daylight balanced compact fluorescent has a completely different story to tell. As expected, the histogram shows a light that is much closer to what the camera expects for daylight. As you can see, it is a nicely close match to natural sunlight. Not only are we getting a white patch that looks white, the colors in the chart are vivid and easily discernible.

For the record, this is not one of the expensive bulbs that you get from the camera shop. This is an inexpensive CF bulb bought off of the Internet for around $5.50 each. If you need a decent continuous light source on the cheap, this is it.

Taking a reading of the middle gray patch I get (91, 96, 90). While not absolutely perfect, this is good enough to use without any additional white-balance adjustment.

Lightsource: 200WS Studio Flash set for f/5.6 Predictably, the daylight photo gives us a nice white that is very much like the daylight balanced fluorescent, except without the odd peaks. It is no surprise that a strobe (flash) is considered the best light source for photography. Not only does it provide a lot of lighting power for a small amount of energy, but it is very close to the spectrum of natural light. A flash can be mixed with sunlight with no corrective filters.

A reading for the middle gray patch gets (93, 93, 93), a perfect match. I do have a confession to make, that was the best reading. Some of the others were (92, 90, 91), (89, 89, 91) and a few other similar readings. Regardless, no matter which you take, this is about as close as you get to a perfect match.

Histograms Compared
In this last image I have put the histograms side by side so you can more readily compare them. The RGB histograms really do tell the story.
This has been a long post, but it addresses an important subject. The series on temperature of light is almost complete, but I still want to cover how to obtain a proper white balance, both in the camera and during raw processing.

Coming Next
In the next posting I will cover the various in-camera white balance settings and will compare and discuss the performance for each. It should be interesting, so stay tuned...


Sunday, May 17, 2009

Temperature of Light - part 3 (An Introduction to Histograms)

An Introduction to Histograms
Before getting into the experiment showing the effect of color temperature on a camera's output, I want to touch on histograms. If you are familiar with histograms, please feel free to skip this little side excursion. If you are not familiar with histograms, then you will need this information to better interpret what follows.

A histogram is a graph that shows the distribution of pixels over for a range of illumination from none to full brightness. The x-axis shows illumination with none on the left and full brightness on the right. The y-axis shows the number of pixels at a particular level of illumination. If you see an area of the histogram with a peak at some point along the x-axis, then you know that the image contains a concentration of pixels with that level of brightness.

Digital cameras represent colored light using three channels of color, Red, Green, and Blue. Using combinations of these three primary colors, we can model virtually any color of visible light. There are other ways to model the color (CMY, HSB, Lab, etc.), but that is beyond the scope of this introductory discussion. The point is that there are three color channels and to get an idea of a light's color content, we need a way to view the information from all three channels separately. If we look at the combined luminance only, then we can make no judgment about color.

Take a look at the histograms in the image above. The black histogram on top represents only luminance. It tells us about the exposure, but contains nothing about color. Below it are three more histograms by color. These represent the luminance for each color channel. In this example, the peak that shows up in the middle indicates that middle gray is a dominant color. All three of the histograms have a similar shape, which tells us that there is a fairly even distribution of colors in the image.

Most subjects we photograph will have a fairly equal distribution of colors, so when looking at the resultant histograms they will have a very similar appearance. Any time there is a big difference between the RGB histograms, either the subject has some dominant color or the there is a problem with the white balance.

Histograms are an important tool for analyzing digital images and are one of the most used tools in the digital photographer's took kit. Much more can be said about the interpretation of a histogram and its use for calibrating exposure and post processing. I hope to touch on some of that in future posting, but for now we have enough understanding to continue with the discussion of light temperature.

Coming Next
In the next posting I will continue the series with a demonstration of what the camera sees when photographing under different light sources. Stay tuned...


Wednesday, May 13, 2009

Temperature of Light - part 2 (Artificial Light Sources)

Now that we've covered natural sunlight, let's take a look at some common artificial light sources and compare them against sunlight. The following chart shows three light sources, sunlight, incandescent, and a daylight fluorescent. I haven't yet found a chart for a studio strobe light, but it should look quite similar to the daylight fluorescent, but without the sharp peaks (we discuss that a few paragraphs from now).
The chart below shows light from beyond ultraviolet down through infrared. The visible spectrum is shown as a rainbow fountain fill from violet to red. This chart is only an approximation of the characteristics for these light sources. The colors shown are not a perfect representation, but are intended only to mark where visible light starts and stops. The numbers along the x-axis are the wavelength specified in microns and the y-axix is amplitude in unspecified units.

Looking at the chart, one of the first things to notice is that the sun's emissions (dotted black line) are strongest over the visible spectrum. This of course should be no surprise whether you are an evolutionist, a creationist, or anything in between. Our eyes are optimized for the light that is most prevalent on earth and this chart confirms this as fact.

Incandescent Light
The oldest continuous artificial light source of which I am aware, is the incandescent light bulb (dashed red line). Although it is a continuous spectrum light source, it is interesting to note just how little of this light's output falls in the visible spectrum. Its output curve is slanted heavily toward red and contains only a small amount of blue or violet. Even its strongest color within the visible spectrum falls far below its main concentration of output in the infrared. Most of the energy from an incandescent bulb simply gets expended as heat. This, along with a spectral content that is not a good match for sunlight makes the incandescent light source far from the ideal photographic light source. The amount of power required for good illumination will tax the wiring of most any building and the heat generated will cause our poor subject to perspire (or pass out).

For years photographers used incandescent lights with special coatings that improved the spectral content. Nonetheless, these lights require immense amounts of power to achieve reasonable lighting levels and they get extremely hot, to the point that many, myself included, consider them unsafe and a bad choice considering the available alternatives.

Daylight Balanced Fluorescent Light
The daylight balanced fluorescent bulb is one of the wonders of our modern technology and actually does a nice job of lighting. This continuous output light source outputs a continuous spectrum of light that closely mimics the visible spectral output of the sun. The intensity tends to be a bit low, but you can see from the chart that it has a basic curve that is similar to sunlight. The balance of emissions for a properly designed daylight bulb is close enough to a sunlight that you can use the sunlight setting on a digital camera's white balance with very good results. Note that very little emission falls in the infrared, which is indicative of the excellent efficiency for this type of lighting. As light bulbs go, these operate with very little heat.You will note one small anomaly with this light source. There are two large peaks in the output, one at about 430 microns and another at about 540 microns. Fortunately, our eyes tend to average out the light's emissions and so we don't notice these peaks. Because one does not encounter pure colors in real life, the peaks do not significantly impact the light balance for a digital camera.

Overall, my view is that a daylight balanced fluorescent light source is well suited to photography. The negatives for this light source are that the intensity degrades and the spectral output tends to shift over the life of the bulb. Also, the intensity cannot easily be varied, so most light fixtures that are based on this technology, use arrays of bulbs that get switched on or off to obtain a desired output level. This of course limits the number of settings and increases the expense.

Studio Strobe
A studio strobe outputs a very bright pulsed light with a continuous spectrum that closely matches daylight. On account of this, it is one of the best artificial light sources for photography. Because it is pulsed, the energy required is very low compared to a continuous light source. The power output for a studio strobe can be accurately controlled over a broad range of power settings. The significant disadvantage is that the photographer cannot see the lighting until after making the exposure and processing the resultant image.

To allow the photographer to visualize the lighting, most studio strobes come equipped with incandescent modeling lights. These are much lower power than would be needed for most purposes, but allow one to at lest see where the shadows fall. Typical wattages are around 150 – 250 W. They tend to generate a fair amount of heat, as is common for all incandescent lights. In the future, we will likely see then incandescent modeling lamp replaced with LED based modeling lamps.

For more information on artificial lighting sources, visit the National Lighting Product Information Program website.

In the next postings I will begin to demonstrate the effect of using the light sources that have been discussed and how one can effectively achieve a proper white balance whether shooting raw or jpeg.

Until then,


Continue on to "Temperature of Light - part 3 (An Introduction to Histograms)

Monday, May 11, 2009

Temperature of Light - part 1 (Introduction)

This next set of postings will deal with the temperature of light. This is a rather broad subject and really warrants some additional reading, but I will attempt to offer up a very basic background of the physics and touch on the more common issues with how the temperature of artificial light affects photography.

In the first post of this series on light I touched briefly on what light is. In this last section we are going to be discussing an aspect of light that is very dear to photographers, namely the temperature of light. This is sometimes referred to as the color of light, but it more properly refers to the spectrum of light.

Any light source, with the exception of a laser, will emit a variety of colors, some more than others. When the source approximates the spectrum emitted by the sun, it is said to be a full spectrum light source. The sun emits light in all of the visible colors, but not all of the colors are emitted at the same intensity. Sunlight is also affected by the earth's atmosphere, so the light that we receive on earth is certainly not the same as the sunlight in space, nor is it consistent from day to day. In fact, here in the Seattle area it is not consistent from minute to minute due to our ever changing weather. However, on clear days, the emission of light from the sun is relatively consistent, and so this is what gets used as our standard for a model of sunlight emissions.

The Wikipedia tells us that “Color temperature is based upon the principle that a black body radiator emits light whose color depends on the temperature of the radiator. Black bodies with temperatures below about 4000 K appear reddish whereas those above about 7500 K appear bluish.” This reference is based on the kelvin temperature scale and is commonly used to describe light for photographic applications. Essentially, you heat up a black body and at some point it starts radiating in the visible light spectrum, starting with red. The more it is heated, the more the emissions spread toward blue, violet, ultraviolet, and beyond. If we heat it to 6000 K, then we get light emissions that approximate noon day sunlight. Go a littler hotter, say 7500 K and the light gets a somewhat blue. Go a little lower, say 4500 K and the light gets somewhat reddish. Do note that in spite of the temperature, blue is considered a cold color and red is considered a warm color. This comes from the mood of the color and has nothing to do with its kelvin temperature. For more information on color temperature, visit the Wikipedia or do a Google search.

Here is a chart showing the emissions of sunlight (approximate) for a cloudless day. Note that its emissions extend into the ultraviolet on the left, and far into the infrared at the right, but the majority of its spectral intensity is concentrated within the visible spectrum.

Light sources are rated as either continuous or non-continuous. A continuous light source will reproduce light across the entire range of visible light, from red to violet. A non-continuous light will produce only some of the colors from the visible range. An example of continuous light is a standard incandescent light bulb. While it is very weak in blue light, it does contain enough light across the visible range that our eyes are able to properly identify colors when illuminated under this lighting. An example of non-continuous light is a sodium vapor lamp, which produces mostly an orange/yellow color and has virtually no blue color. If you view a color chart under a sodium vapor lamp, you will see a very poor rendering of color, such that everything will have a distinct orange tint and many colors will not be discernible.

When we consider light sources for photography, we obviously want to use a continuous light source so all of the visible colors can be seen. Our eyes are optimized for sunlight and consequently, our digital camera's sensor and image rendering has been optimized to mimic the way our eyes see. Because of this, we would like a light source that closely matches the emissions of the sun, within the visible light spectrum. Ideally our light source will contain little or no ultraviolet and little or no infrared. The camera's sensor is sensitive to both infrared and ultraviolet. Most digital camera sensors use filters and coatings to reduce the absorption of light outside the visible spectrum, but the effectiveness of these filters vary and there are trade offs with light loss and cost.

In the next post we will take a look at some common light sources and discuss their characteristics and suitability for photography.


Continue on to "Temperature of Light - part 2 (Artificial Light Sources)

Wednesday, May 6, 2009

We Interrupt This Blog...

I don't like interrupting a related series of postings, but this is a time sensitive message that may be of value to someone.

I spent six hours (plus travel time) at the Bellevue Hilton Inn last night to see David Ziser's “Digital WakeUp Call” seminar and I must say that David offers an impressive amount of information and goodies for the money. For me it was worth every penny and much more. David has many years of wedding photography experience and shares his approach to shooting, work flow, and business. There is a lot of information that transfers to studio photography, if not directly, then in concept. I highly recommend that you attend this seminar. At a minimum I guarantee that you will glean something of value. Often it is the little things that make the big difference. Go if for no other reason than to win a door prize. They gave away literally thousands of dollars worth of prizes and will be awarding a grand prize some time during the tour. Now, your's truly did not win any prizes, but happily, everyone came away with the following:
  • One year membership to WPPI (Wedding & Portrait Photographer's International), which is a $100 value.
  • DVD with 4-hours of extended tour content,covering lighting, lightroom, photography, Photoshop, marketing, & software, with tutorials from Scott Kelby & Matt Lkoskowski, David Ziser, and some vendors (show sponsors).
  • Free offers and discounts from PPA (Professional Photographers of America), Zookbinders, Animoto, NAPP (National Association of Photoshop Professionals), SendOutCard, American Color Imaging, Professional Photographer Magazine, & BellaGrafica.

Let me give you a quick rundown on the sessions.

The first session was the longest and focused on lighting and how he got the lighting seen in the many resplendent photos that he shared in the form of 24” x 36” prints and in his slide presentation. Many of these appear as if elaborate lighting setups were used that must have taken considerable time. In reality, as David shared how he got the light, we could begin to understand how very little equipment can be used to make awe inspiring photographs. All were done with just one or two portable flashes and a reflector or bounce off of some available surface (even a person's white shirt). What impressed me about this segment was his ability to see light everywhere and the potential in virtually everything. If the lighting didn't exist, he made it happen using whatever tools he had at the moment. Weddings can be fast moving, high pressure affairs, which often leave little more than fractional minutes for setup and execution of a shot. Of course, there is always the photographer's lie, just one more shot, but even that buys only a little more time. With just a handful of gear and an understanding of light, David has made wonderful portraits in moments. It isn't rocket science, just a good understanding of light and an out of the box view for the potential of anything to interact with light. This is a subject that is near and dear to me, as I'm sure it is for every studio photographer.

The next section covered silver bullet techniques that he uses to speed up his work flow. This section covers mostly the software that he uses and endorses. It gets a bit commercial, but is well worth wading through because of the demonstrations. Of particular interest to me is a program called LumaPix Extreme 4. I thought that Corel Draw was the fastest way to do free form layouts, and of course, there are things that only it can do, but LumaPix Extreme 4 does most of what Corel can do and it does it many times faster. It comes equipped with awesome templates for a starting point, and has an automated setup wizard that can create an entire album (100+ photos) in a few seconds. It appears to be the perfect tool for setting up a photo montage, poster, senior book, family book, wedding book, and about anything that needs photos and text, or I should say graphic elements, arranged in a format suited to the genre and with a very polished professional look.

The last part of the seminar focused on the business aspects of running the business. This segment covered ways to make your business more profitable. Virtually everything David covered in this section is directly applicable for the studio photographer. David discusses how to leverage our relationships with vendors and other associates to increase our visibility in the local community. As he says, “get to know the people doing business with the people you want to do business with.” I don't want to attempt to reproduce his information here, but just let me tell you that it is reliable and relevant for today with an eye toward the future. Even for someone with honed business and sales skills there is fruit to be gleaned. For the rest of us it is life giving, crystal clear water fresh from the mountain stream.

I will get back on track with the series on lighting starting with the next post, but felt that this seminar is so good that it merits interrupting the series. If you are at all on the fence about going, just sign up and be there!