Thursday, July 7, 2011

Coming Soon

IMAGINE A light source, which can automatically match the color of ambient light.

So many times I've taken interior photos, with the room illuminated by tungsten lighting; however, some light comes through the windows, but that looks strongly blue and so harms the photo. For my best work, I adjust the color of the window lighting and the artificial lighting separately in Photoshop, but this is time-consuming and error-prone. Big-budget cinematographers will put colored gels over the windows to get the light colors to match, or they will put gels over their lights. But the use of gels has the unfortunate side-effect of decreasing the light intensity, requiring even brighter and hotter light sources, much to the dismay of the actors.

Rift Labs is developing a three-color lighting panel which has variable color temperature. Using low-power, three-color light-emitting diodes, their forthcoming light panels will automatically be able to match any lighting situation. Or, any color of light can be dialed-in, and the brightness of the lighting does not change.

So photographers and cinematographers can have a portable, battery-operated, low-cost lighting system which can quickly and conveniently produce the color of lighting needed. A good use of this would likely be for fill-in lighting, an augment to ambient lighting. Portable, battery-operated white-light LED panels have appeared in the last couple of years, causing much excitement, but Rift is taking this to the next level.

The organization is making these lighting units open-source, and provide the circuit diagrams and controller software free of charge; if their concept proves usable, we ought to see many similar designs produced at low cost in the near future.

I noticed that they are having trouble finding the correct method of producing a uniform illuminance under a change of color temperature. This is likely to be problematic for them, since the sensitivity of digital cameras to various color temperature conditions is variable across manufacturers and models of cameras.  See here. They may need to adapt their system to include color calibration data specific to particular kinds of cameras. Likely this will merely require a custom color transfer matrix — nine numbers — that will provide closer mapping between what the camera sees and what the light source delivers. This color matrix could either be encoded as a camera model database in the device firmware, or the user could type in the numbers if they know them. A more clever method could be a built-in algorithm for color calibrating the camera: this little feature could be a strong selling point.

I also wonder about the color quality produced by this kind of unit. Since it uses only three colors — red, green, and blue — it may not operate equally well under all color gamuts used by digital cameras. Please recall that it is impossible to mix all possible colors from only three primary colors.  However, if they concentrate on getting sRGB right, then this unit ought to operate well for 99% of uses. But there will still be metamerism problems: colors that look identical to the human eye will look different to the camera, and this kind of three-color lighting will make metamerism failure even more prominent. They may find they get better performance if they also include some other colors in their LED array to provide a more uniform spectrum.

This kind of lighting could be of great benefit for those who shoot RAW. Digital cameras have a fixed white balance: this raw data is processed to produce images correctly balanced according to the color of the light. However, lots of the RAW data is thrown away during this processing, which leads to increased digital noise, particularly in the red and blue channels. The Rift Labs product can be adjusted to produce a magenta light which will accurately produce an accurate RAW light balance: no data is thrown away, and the noise level is reduced to its practical minimum. This is likely only of interest to specialists, but it does show how useful this device can be.

UPDATE: Click here to read an article on color rendition under LED lamps. You may expect color shifts with using these kinds of products.

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