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Monday, March 26, 2012

••◊ The Academy's Take on Lighting, History and Future

If you can't already tell what's on my mind lately, this should cinch the deal.  I was hunting around the Internet-webs looking for information on lighting and came across the Wikipedia page on Color Rending Index (CRI).  It's an interesting read on the history of understanding lighting, however what I found more fascinating was a comment in the article about LEDs not being optimal for film lighting.  I can sort of understand why given the poor color rendering index, but I was still curious about what they found.

A simple Google search landed me on the correct Academy of Motion Picture Arts and Sciences page discussing their report on solid state lighting (i.e. LEDs).  Going further down the rabbit hole there was the Academy's 1928 report on the "new" incandescent bulb technology on the right side of the page.

Oh, how technology changes.  Now days incandescent lighting is considered that old power hungry technology that your local congress member wants to outlaw!  However, back then it was arc lights or the new fangled incandescents.  Some of the interesting comments I saw in the report include... (please note that "Mazda" was used interchangeably with incandescent in the AMPS report)

Replies from nine studios, to Questionnaire No.1, brought forth a uniformity of opinion that the substitution of Incandescent lighting would reduce electrical labor costs approximately 50%.

"Lightness of equipment and hence ease of portability which insures quicker setups as well as lining up of sets; quick adjustment to photographic alignment and subsequent accessibility."
-Karl Struss, Chief Cinematographer for D. W. Griffith

Labor-7 men $7.00 per day. 49.00

There was general agreement in the replies that current costs were materially reduced by the substitution of Incandescents, The current costs on Universals "No. 13 Washington Square" was given by F. Graves as $41.08, as compared with an estimated current cost had Arcs been used of $615.93. Paramount estimated 78 cents current cost per hour for Incandescent, as compared with $1.38 for Arcs.

"In photographing small or medium sized sets of no bigger floor space than 750 square feet or 18 feet in height, the Mazda units, such as broadside domes and strips are very practical for general illumination, but for sets of. larger area or greater height, from my experience, I believe one should incorporate Arcs in the lighting."
Harvey Leavitt, DeMille Studio

"Arc equipment give more general and concentrated light than Mazda on large exterior shots.  We can never hope to get as concentrated light source in Incandescents using Tungstens, as we now get from Arcs"
-Paramount Experimental Department.

"Incandescents, due to the filament, cast a "fuzzy" shadow regardless of the reflector being used or the number of lights."
-R. B. Mclntyre,Production Manager, Samuel Goldwyn.

"We get a greater degree of roundness and softness with the Incandescent light."
-J. M. Nickolaus,M. G. M.

Mazda will be used almost exclusively in the future."
-Paramount Experimental Dept.

These are almost the same arguments given for and against tungsten incandescent lights today!  Speed, ease of setup, operating cost, quality of light, lighting crew costs...etc, still apply.  Only now days people are using Kino's and Litepanel's to substitute in for incandescents.

It's also interesting to note that they studied the spectral characteristics of each light type since even black and white film stock has it's own spectral response, much the same way CMOS sensors do today through their Bayer Pattern color filters!

Technology moves on.  I'm going to try to dig into the solid state lighting discussion they offer through a series of symposium videos.

Monday, March 12, 2012

••◊ Color Rendering and CMOS sensors

A common question I get is about lighting and why one light is more desirable than another, so I thought I would take this opportunity to answer that question in more depth.

The first thing to address is the characteristic of certain lights.  Let's start with the classic orange finger scorching tungsten incandescent bulb.  This is essentially a fancy heating element that happens to put out *some* light.  I stole of a picture of an incandescent bulb spectrum from here.  For those less familiar with wavelength versus color, the 400-500nm range is generally violet-blue,  The 550-650nm range is generally green-yellow-ish.  The 650nm and above range is generally orange-red-ish.  So looking at the graph below, violet is on the far left, green in the middle, red on the far right.  As you can see a tungsten bulb is generally missing blue and is lacking in green, leaving more yellow-red in the spectrum.  Typically a tungsten video light is rated at 3200K and a household bulb might be 2700K - lacking even more blue and green. 

Next, we can explore a fluorescent bulb. These bulbs come in a variety of color temperatures, however for video we generally stick with a color temperature of 5500k for reasons I'll get to later.  For this comparison I stole a picture from Kino-Flo here.  A Fluorescent bulb generally puts out UV light that is then translated to a wider spectrum by coating the glass bulb with a phosphorescent substance.  In the spectrum charts below you can see the UV spike down around 420nm.  Anyone that's been to a science museum is familiar with the green glow of phosphorus, thus the green spike around 550nm.  Those characteristics are fairly independent of the rated color temperature of the bulb.  They just use different amounts of phosphorescent substances to change the perceived blue-orange ratio of the bulb to get somewhat close to a color temperature rating.  A lot of the time I put a gel over fluorescent fixtures to trying to calm the green spike behavior a little.

Obviously the hottest trend on the market is LED lighting.  They aren't quite the panacea that everyone thinks they are, but they do offer quite a few advantages in power, portability, and general usage.  Every "white" LED is actually a blue LED that has an optical coating that broadens the spectrum to appear "white", just as a fluorescent bulb does.  So the result is that you see a blue spike in the spectrum, with a lump in the rest of the spectrum where the phosphorescent material emits light.  I stole a picture from the Philips Lumileds site here.  So, just like a fluorescent bulb, a LED can be made to appear to be just about any color temperature by changing the coating.

The real question is, why does this matter?  Well... our cameras are designed for broad spectrum daylight.  Typically the "native" color temperatures of CMOS sensors are in the range of 5000K-5600K, making daylight range color temperatures more desirable to use with CMOS sensors. 

First, I think I need to define what I mean by "native."  The color filters on the image sensor itself have a certain balance of red/green/blue.  If, for instance, the native color temperature of the sensor is 5200K and you have a light source that is perfectly 5200K the white balance of the sensor will be dead-on.  There won't be a need to adjust the ratio of red to green to blue because they are already balanced by the sensor's color filters.  If you use the same sensor under a tungsten bulb (3200K) then the camera's processing circuitry has to greatly boost the blue channel, thus creating more noise in blue.

From reports I've read the "native" color temperature of the Canon 5D mark II sensor is about 5200K.  The Arri site lists the native color temperature of the Alexa CMOS sensor at 5600K Jim Jannard rates the native color temperature of the Red MX sensor at 5000K.  There's nothing inherently wrong with any of these ratings.  They are what they are.  I used a mix of tungsten, fluorescent, and LED this last weekend on a shoot with the 5D mark II and I think it came out fine at a low ISO setting.

The other reason the spectrum of these lights matter is that it effectively changes the color rendering of camera, even when custom white balanced to the particular light source.  This is especially true with a very "spikey" spectrum such as a fluorescent bulb or LED.  Maybe I'll save that for a future blog entry when I'm feeling techie again.  For now I'll just point to the Wikipedia entry on Color Rendering Index (CRI).  This is where a color test chart, such as the DSC Labs charts, come into play.

Sunday, March 4, 2012

••◊ What Would a Ninja Do, In Boise?

If you were a Japanese assassin left to fend for yourself in a city of 202,000 what would you do?  No sushi, no Godzilla; just a face mask, a sword, and Chinese throwing stars.  That's what a colleague's poster attempted to answer.  This is just a for-fun post about my whims of what a ninja does in a state capitol after a long day at the office - although I'm not implying any ninjutsu skills on my behalf.

There's always a "stealth attack," however the only thing close to security monitoring around the state capitol building is about 20 "occupy Boise" protesters camping on the lawn of the next door building.  Seems like kind of a waste of ninja training.  This was in opposition to when I visited Washington DC and felt like I was going to be strip searched and interrogated by the CIA for just walking down the National Mall with a camera.

A ninja could always go downtown and "unleash fury," however most businesses seem to be closed before 7pm on Wednesday night.  You can see all two people on the street.  Again, a waste of ninja training.  Maybe my next film should be "Ninja in New York!"  You're lucky if the pizza place across from your hotel closes before midnight there.

A ninja could meditate with the views of nature.  This seems appropriate, given the two failures above.  The panorama below is actually the view from our office building.  Definitely a nice thing to see in the morning as I approached my remote work site.  ...and yes, Boise is *that* brown in winter.

After unleashing fury, a ninja could clean up after himself.  After all, it seems like the more honorable and respectable thing to do.

When I was younger and had a fantastic, but parental motivationally flawed idea, it was somewhat common for my mom to reply, "yeah, when pigs fly!"  The corporate engineering department seems to have that issued solved.  Sorry mom, you're going to have to come up with something better, but the second picture says it much better.