The Color Managed Camera
The evolution of digital cameras has reached a new point. Picture control has been taken to a new level. Digital cameras can instantly and easily be color managed.
2000: Digital cameras are gaining acceptance among professional photographers
2005: RAW file format was accepted as superior by all serious photographers
2011: RAW profiling of digital cameras became easily manageable by all photographers thanks to the introduction of QPcard 202 and 203 color reference cards and QPcalibration application
About light and color
Heated black-body is the common scientific name for light sources like the sun and tungsten light bulbs. What they all have in common is continuos spectral distribution of visible wavelengths. This makes them quite easy to grayscale balance (white or gray balancing). However, grayscale balancing only takes care of different color temperatures of the light (compensates for warmer or colder light), not camera specific on-sensor filter qualities or signal processing and un-even spectral distrbution of artificial light sources like fluorescent light or LED.
Strictly speaking visible color is depending on two components: colorants and light. If there is no light, colorants will remain invisible. Colorants can be transparent and transmit light - like in the filters of a scanner, in a positive slide film, on a camera sensor, in a monitor display or in a video projector. Colorants can reflect light - like paint on a canvas or ink on a printed paper. And colorants can be emitted from a light source – like a colored LED.
Light can be emitted from a heated black-body like the sun or a tungsten light bulb, resulting in continuos spectral distribution. Or it can be artificial with an intermittent spectrum like in fluorescent light. No matter what, visible color is always a combination of colorants and light.
Color management is the discipline of managing colors in digital images
The imaging business (photography and printing) has gone through revolutionary changes over the last 15-20 years. The analogue imaging world is left behind us in favor of a digital image environment. The transition, or even paradigm shift, has taken many years and cost lots of pain. There have been many obstacles to pass and photographers and other imaging professionals have had to learn completely new ways of handling pictures. Fortunately the gain is enormous and well worth the struggle and no one wants to go back to films, chemicals, waiting times and uncertainty.
The two key words for success during the digital transition are spelled "Color Management". We have to manage colors in a completely different and sometimes obscure and abstract way. Color management has been and still is very difficult to comprehend for many photographers and other image disciplines like post processing, separation, printing and web publishing. We have to manage colors in scanners, in monitors, in printers and in cameras.
Every single unit used in the process of handling color images has a specific characterization. Scan a picture in 10 different scanners and it will come out differently in all of them. Display a picture on 10 different monitors and it will look different on all of them. Print a picture with 10 different printers and all prints will look different. Take a picture of a specific subject with 10 different cameras and all pictures will come out differently. So, in order to make these units communicate colors in an accurate way, they all have to be color managed.
Let's make a comparison with a digital thermometer. You put the sensor in ice water and check the scale. It shows +3°C. When you dip the sensor in boiling water it shows +96°C. You know that ice water is 0 and boiling water 100°C. You have now characterized your thermometer. If you like, you can do the same thing with nine other thermometers and get characterization of all of them.
Before we get deeper into temperature management and profiling, let's calibrate the thermometer. There are two small calibration knobs on the thermometer display; one for low temperatures and one for high. Put the sensor in the ice water again and adjust the first knob until it shows 0°C. Repeat with boiling water, but this time use the second knob for calibration. Adjust until the display shows 100°C. Go back to ice water and fine-tune to 0°C. After a few adjustments you have calibrated your thermometer.
Profiling the thermometer is a different task that involves computing. You create a LUT (Look Up Table) and send the temperature information through the LUT before displaying the results. If the thermometer signal says +3°C, then the LUT tells the display to show 0°C. If the thermometer signal says +96°C, then show +100°C. Everything in between can be interpolated and everything below 0 and above 100 can be extrapolated, with more or less accuracy. The LUT in the profile could be replaced by a mathematical matrix doing basically the same job as the LUT.
Next concept in temperature management is linearization. With 0°C and 100°C fine-tuned and correct; can we be sure that 50°C also is correct? Of course not! In order to more accurately display all temperatures between 0 and 100, we should check some increments (like 25°, 50° and 75°) and, if necessary, adjust for them as well. This adjustment or correction can be incorporated in the LUT or matrix of the profile.
Now let's take a look at the concept color gamut. The analogue for our temperature world would be "temperature gamut" and it is defined as the difference between maximum and minimum temperature of the thermometer display. Let's say max is +120°C and min -40°C. That gives a temperature gamut of 160. We can accurately record temperatures between -40 and +120. If the real temperature is above 120, the display will in-accurately show 120. The temperature is "out of gamut" and we have absolutely no idea if the recorded temperature is 120,1 or even 957,3°C
To be or not to be color manageable
Take a picture of or scan a color target. Show the color target on a monitor and print it with a laser, inkjet or commercial offset printer. If you don't manage colors in a scientific and tedious way, you will most certainly end up with a result, maybe resembling, but for sure not being exact like the original color target.
The good thing about a scanner is that the separation filters and the light source always are the same. OK, they will change over time, but basically speaking: it is color manageable. Meaning if you have a known color target and an appropriate application you can quite easily linearize, characterize and create a color correcting profile for the unit. You scan the target once, run the application and you have a scanner profile. Next time you scan an image, you run the scanned result through the profile and it will adjust the colors accordingly. You will end up with a digital image, not only resembling, but being almost exactly the same as the original. That is of course within the color limits of the scanner being used. If the color gamut of the scanner is greater than the color gamut of the physical image, it is possible to, without any problems, create a digital replica with "exactly" the same color values.
The good thing about the monitor is almost the same as the with the scanner; it has color filters and a light source that are stable. The monitor is color manageable, and in an even easier fashion; you don't need a physical target. It is all in the application. The drawback is that you need a measuring device; a colorimeter or a spectrophotometer. On the other hand, if you choose the right device, it can be used for profiling of your printer as well. What you do is to put the metering device on the centre of the monitor screen, start running the application and wait. The app will display a series of different familiar colors on the screen, ask the measuring device how those colors comes out and create a monitor profile taking care of the deviations. There is linearization and adjustment of color temperature involved as well, but basically it is a very simple task manageable by anyone with basic knowledge in computer operation.
Just a short note on monitor color temperature. The international standard for photography and printing says 5000K is the correct color temperature for viewing and visual evaluation. However, it is important to understand that the monitor adjustment does not affect the digital image per se, it only affects how the digital image is presented on the monitor screen. When you change the color temperature of the monitor, the only thing that happens is that the image is displayed as warmer or cooler. In order to recognize the colors of the displayed image correctly you have to consider how your eyes are color managed or rather white balanced. More about that later.
The good thing about the printer is that the inks being used are the same over time. The color of the paper in use can vary and different papers might need individual profiling, but basically a printer is easy to color manage - it is color manageable. Just print a familiar color pattern, measure the result with a spectrophotometer and let the application do the rest.
You will end up with a customized printing profile that is able to tweak the colors of the image to be printed, making them come out correctly on paper. Again - within the printer's color gamut limits. If the color gamut of the printer is smaller than the color image to be printed, we need to adjust the colors in way that is called color mapping. The gamut of the image is compressed by means of reducing saturation.
The "color managed" eye
Human eyes are extremely adaptable to different color temperatures. The most suitable environment for examination of color images is, in it self, color free. Neutral mid gray walls, a gray background on your computer screen and no colored post-it messages on the monitor frame. The perfect environment also has ambient light of moderate strength, preferably with spectral consistency and around 5000K. Your vision will be normalized by, or adapted to, the colors and light of the environment.
Now to the most important matter regarding color managed human vision: the neutral gray of your computer monitor desktop (monitor background) has to color temperature-wise match the gray surroundings (in the room) illuminated by the ambient light. If one of them is lighter is of no or little importance, but they have to be experienced as equally neutral gray. Most probably you can not adjust the color temperature of the ambient light, so the important matching has to be managed by adjusting the monitor's color temperature. Now, what if the color temperature of your monitor is not 5000K? It really doesn't matter - as long as your eyes are adjusted to the actual monitor color temperature, they will recognize the colors of the displayed image correctly. More about monitor color temperatur matching here.
The color managed camera
The most difficult item to color manage in the image workflow is the camera. Like profiling a scanner, a monitor and a printer, profiling a camera takes care of individual differences in different camera brands. But unlike the other units, cameras are used in a wide variety of lighting situations.
"But if I use a neutral gray target like the qpcard 101 or 102 or the Spider Cube and make a custom white balance setting in my camera, then I must be all safe and clear?".
No you are not! Custom white balance setting is of course better than relying on the camera's built in automatic white balance, especially in difficult lighting situations, but it only takes you a small part of the way towards the color managed camera. White balancing is not changing the shape of the RGB curves, it is only changing the balance between them; their position. With RAW images white balancing can be performed in the post processing in the RAW converter with exactly the same result as in the camera. Real color management means position adjustment and curve tweaking.
Camera color management, much more complex and accurate than ordinary white balancing, is quite easy to understand theoretically. And, the color managed digital camera is now at every photographers hands thanks to QPcard 202 and 203 and QPcalibration. You no longer have to rely on generic camera specific RAW profiles. From now on you are in full control of the profiling process.
Start creating your own custom RAW profiles, specific to your camera and a chosen light. This profile will most probably improve the colors of all your images, including older images taken with the same camera. This profile will become your every-day-profile, useful in most lighting conditions.
The second step is to take color fidelity one step further by creating light specific profiles. This is the best way to exploit your cameras full color potential. You will be amazed by the color difference when you compare images converted with your old generic profile and a QPcard (camera and light specific) profile.
The third step is to explore mastering "impossible" light. Modern energy efficient light sources, like fluorescent or LED, show great spectral differences when compared to the sun and tungsten light sources. The spectral distribution is intermittent with spikes and spaces, making colorants reflect or transmit visible light in an inconsistent way. Some wavelengths of the colorants are boosted while others are suppressed. This makes simple white balancing impossible to use with acceptable results. Color management and profiling, however, can greatly improve pictures taken in the light of these modern sources.
Restricting or promoting creativity?
Q) Isn't there a risk that the technical operation involved in profiling a digital camera kills creativity?
A) We are convinced that it works the opposite way. Yes, profiling a camera is technical and non-creative. It involves reading a (short) manual and some computer operations. We have put down a lot of effort in making the camera profiling operation as easy going as possible. After a while, creating profiles is nothing but a routine task. You start with a standard profile that works most of the time. Then you continue making light specific profiles for difficult lighting situations. Profiling for difficult light is actually making post processing a lot less tedious and thus helping freeing your creative mind.
When profiling becomes a routine task, it doesn't limit your creativity at all. In fact the result means broadening of your creative mind. Post processing can easily become a tedious task where you end up spending hours manipulating your pictures to a state corresponding to your inner vision. Customized profiling results in correct colors and optimal color gamut as a starting point, making post processing so much easier. To start from a favorable position means not only less time spent but also improved confidence and, most likely, better end result.