Tuesday, April 29, 2008

NAB Odds and Ends

I’m a bit late in writing this, but there are some NAB wonders that I want to blog about. I had all of one day to see the show, but I did see some pretty cool things. How can you not at NAB?

I spent Sunday through Tuesday working in the Element Labs (elementlabs.com) booth. I’ve been consulting on their lights for a little over a year now, helping them develop a broad-spectrum LED light for the motion picture industry. Most LED lights are made of single LEDs that appear to be white (although many skew slightly green) but if you look at the spectrum you’ll see a very sharp spike: they don’t emit much of the color spectrum. As you only get accurate color reproduction if you hit an object with light containing its color, you won’t get very accurate color from a narrow band light source.

Element Labs uses six LED (three each in two packages, alternating across the fixture) to create broad spectrum light. The mixture of LED colors provides for more accurate color response, and it also allows the fixture to change color temperature. The current spec allows for 2200k to 6500k, and it’s a very pretty quality of light.

Last year I worked with Element Labs to create a process shot in the booth. Their original product line consisted of large video wall displays, and several DP’s have used those video wall products to create traveling light for process shots. The idea is that you can hang the panels above a car on a green screen stage, and then play your background plate back across the video wall to create interactive lighting between the plate, which will be added in post, and the actors on the set. Last year we did exactly that, by creating a video wall that reflected in a Shelby Cobra that was parked in the booth. The model in the car was lit with earlier versions of the LED light that we’ve been developing, and the display was a huge hit. This year we scaled down to a motorcycle without a model, so the display was a bit less dramatic but it was still fairly pretty.

The great thing about working a booth for several days is that people come find you. I got visits from a lot of people I know through CML (cinematography.net) as well as a Panavision rep and the president of my IA local.

My free day was reasonably well planned out. My first stop was over at Schneider Optics, to visit Bob Zupka and see their new IR cut filter for the RED. We had a long talk about the complexities of filtering, which once again proved to me that I frequently have no idea how much I don’t know, and then he gave me a prototype of the IR filter for testing. Bob has a theory that IR reduction in the RED may improve the overall MTF of the system, increasing resolution noticeably. Adam Wilt and I are going to do that test on Thursday.

I then visited a local producer, Luke Seerveld (seerveldmedia.com) who was working a booth for a company called Prompter People (http://www.prompterpeople.com/). They specialize in making cheap but useable gear for the production industry. Is a $500 tripod a good buy? In this case, yes--it’s not an O’Connor or a Sachtler but it was darned good for a cheap tripod. They make LED lighting units that are decent--not great, they’re a bit green and spiky, but decent--for very little money. Add 1/4 minus green and your good to go for most purposes. They’re probably not great on color rendition but they’ll work for a number of less critical applications.

I stopped off at a couple of other locations before making my way to Tiffen to see their IR filter. I spoke with one person who was in sales and didn’t know much about the IR filter, but she pointed out the gentleman I should talk to and I waited patiently while he helped someone who was obviously new to the business understand the basics of filters. He recognized my name from an article draft I’d recently sent over (I wrote an article on HD filtration for a future issue of HD Video Pro that I sent over to Tiffen for vetting) but continued to spend a lot of time demonstrating consumer camera support tools to the person ahead of me. After waiting 20-30 minutes I gave up and left.

I met up with fellow DP and rental house owner John Chater (chatercamera.com) at the Tiffen booth and we walked over to BandPro (http://www.bandprodigital.com) to see the Sony F35. I really like the external design of the camera, and I was amazed at the latitude I saw in the image. Looking across the aisle into the Sony booth I was able to see deeper into shadows than I could by eye.

I’ve learned that a good way to analyze a camera’s limitations is to look at highlights, as well as bokeh, to see what happens when the sensor and optics are pushed to their limits. In this case I noticed two things:

(1) Highlights flare vertically, much like an IT chip would, but much softer. It’s not a nasty streak, but a soft and visible flare--almost like anamorphic flare, only not predominantly blue and not horizontal. The design of the chip is rather interesting: instead of a Bayer pattern or three chips around a prism, the pixels are laid out in stripes: two stripes of red, of green, and of blue, repeating left-to-right across the sensor. In post the pixel strips are shifted over on top of each other for full color. When I first heard of this scheme I was worried that horizontal resolution would be compromised, but it’s not--apparently the chip is over-populated with pixels by something like 40% more than it needs.

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Saturday, April 12, 2008

Find me at NAB, part 2

NAB 08 • (1) Comments • Most recent comments by: sam pardue, • Permalink

Saturday, April 12, 2008

Find Me at NAB

For a bit over a year now I’ve been consulting on a new broad-spectrum LED light for the motion picture industry. The idea is that this light, with six different LEDs, can change color temperate with a simple turn of a knob and dim without changing color temperature. The spectrum on this light is much better than current LED lighting products that use only one LED.

In order to see an object’s color accurately you have to light it with light containing that same color. Single LED lights typically use phosphor-based LEDs, which have a little spectral spread to them but not much. They only produce a very narrow range of colored light, so they are good an illuminating but not good at all for color reproduction. The Element Labs Kelvin Tile (the product I’ve been working on) has one phosphor and five dye LEDs mixed together, creating a much broader color palette.

I’ll be working the Element Labs booth at NAB, so come find me if you have a chance. Sunday I’ll be setting up, and Monday/Tuesday I’ll be giving product demos and showing off the new Kelvin Tile “paintbox” control system. Wednesday I’ll be wandering NAB in search of juicy new products.

Here’s where I’ll be:

http://elementlabs.com/nab.html

Come on by and say hi!

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Friday, April 11, 2008

RED Build 15 EI Tests

The idea behind this test was to underexpose a neutral reference and see at what point the RED’s noise becomes too much of an issue. Using Colorista in Final Cut Pro, I put 18% gray at 50 units on the waveform monitor for each exposure, effectively “printing up” each exposure to see how much “grain” (noise) showed up. Some of this is exaggerated by compression artifacts, but I think you can get a good feel for what’s going on.

I’m not sure how this would look on a film out, but to me there isn’t a ton of difference between noise levels at 320 and 640, although I think I’m more comfortable rating the camera at 320. I start seeing reduced contrast at EI 1280, which I really wouldn’t want to try on a paid job.

Compressed via FCP Compressor, H.264.

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Thursday, April 10, 2008

RED IR Filter Test

A while back, while browsing Reduser.net, I saw that someone had done an IR test and discovered that RED has a weakness when it comes to IR filtering. I did my own tests and here are the results:

First shot: RED Build 15, Redcode 36, processed in Red Alert (contrast +.7, brightness +3.0, Kelvin 5130k, all else at presets)
Filtration: Schneider Optics ND .30:

Second shot: same as above, but filtration increased to ND .9 plus ND 1.2--a total of seven stops of ND:

(left to right: PVC’s own HD guru Adam Wilt, and DIT/video engineer Jay Farrington of Chater Camera, San Francisco)

The theory is that when ND filters cut visible light to the point where the ratio between visible light and IR light is very low, the IR shows up much more dramatically than it would otherwise. Normally IR effects are overwhelmed by visible light.

I was a bit confused by this image. The darkest object in the shot--the filter pouch--is made of synthetic fibers and is bright magenta, making me think that the magenta cast in the second picture is an IR issue. But the picture has a magenta cast overall while not everything in the image is radiating the same amount of IR.

I’ve been interviewing Ira Tiffen, formerly of Tiffen, Inc. and a world-renowned expert in the creation and manufacturing of filters, for a magazine article on HD filtration that I’m writing for HD Video Pro magazine. I sent him the pictures above and asked for his expert opinion. This is what he had to say:

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I am making certain assumptions which are commonly encountered. The camera has a built-in IR reduction filter. It is essentially clear to the eye, transmitting most of the light between 400nm and 680nm, which is the visible spectrum, minus the part between 680nm and 700nm. Once it reaches 680nm, the filter begins to reduce light. From 680nm to 700nm, there is a little red lost (which is why this type of filter has a very pale green cast to it), but further above 700nm there is a quickly diminishing transmission of light, all in the IR region. But there IS some transmission from, say 700nm to 730nm, causing a small ‘leak’ in IR. At some higher point, say 900nm, it may start to transmit more light again, but the camera isn’t sensitive to it.

We have to remember that the chip is generally going to have more sensitivity to light in the IR than film does. So a small ‘leak’ in light just above 700nm can be picked up as red by the camera, but with the ND 0.3 filter, at only one stop of light absorption, there is still an abundance of visible light to overpower any leak of near IR getting through the IR filter.

If the camera did not have the built-in IR filter, there would be a much greater amount of near IR light, enough to show a reddish cast on objects (usually black or dark gray) that tend to reflect more IR (remember that dark objects get hotter in the sun than lighter objects- this heat is the excess of reflected IR) and proportionately less visible light. This is why the effect appears even without ND filters when there is no IR filter in the camera.

Here’s what happened in the scene with the ND 2.1 (7 stops, 0.8% transmission) filter combination. All organic-dyed ND filters I have seen, including Schneider’s, begin transmitting an increasing amount of light from about 680nm and up. When there is no ND filter, or a ND filter not much denser than, say, ND 0.9, the amount of additional light in the far red (680nm-700nm) is proportionately too small to be seen among the much greater amount of visible light.

However, with the ND 2.1, the amount of visible light is brought down to less than 1% of the original. The small amount of near red is not affected as much because the filter dyes do not function well in that region. This is the key. So the small amount of far red that gets through is now much greater in proportion to the overall, including the visible, and so a reddish cast is created. Now Schneider ND’s tend to be cooler (read a bit bluer) which is an increase of light transmission just above 400nm, which acts to minimize the reddish cast that would otherwise show up throughout
the image.

In the ND 2.1 filtered image, there is an overall addition of blue in the areas that do not reflect much IR, like the bricks, the silver car, and most other areas. However, in the black filter case, and the gray jacket and sweatshirt, there is a greater amount of light in the far red and IR being reflected, so the reddish cast on those objects becomes enough to overpower the addition of blue that neutralized the red everywhere else.

To recap, without an IR filter the camera would suffer from an excess of red especially in objects that reflect a large amount of IR light. Even without a ND filter.

With just the IR filter, there will generally be a good balance between the visible and the near IR, so that color rendition is normal. The small amount of far red and near IR is overpowered by the large amount of visible light.

With an organically dyed ND filter that is not much denser than a ND 0.9, there is still enough visible light to counterbalance the excess amounts of far red and near IR.

With a much denser ND filter, the overall amount of visible light is reduced enough in proportion to the amount of far red and near IR getting through that there can be a reddish cast through the whole image. With a cooler ND, with some addition of blue, the color can appear normal for objects that do not reflect excessive IR. However, for those objects that do, the amount of IR is enough to still cause a reddish cast because it is then proportionately greater in amount than either the visible light or the increase in blue that worked to counteract it for parts of the scene that do not reflect much IR.

-Ira Tiffen

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I’m extremely thankful to be able to publish this incredibly in-depth explanation of what was going on in the images above. It just shows that no matter how long one works in the industry one can never say, “Now I know it all.” There’s always more. I just love that.

“Now I’ve seen it all” is a completely different matter.

Ira Tiffen is currently working on a book about filtration. He has a publisher but no firm release date. Let’s hope it comes out in the next year or two. I, for one, am dying to read it.

I’m told by Bob Zupka, of Schneider Optics, that they have a filter, called the 486, that was designed for early digital still cameras that didn’t have any effective IR filtering and were extremely sensitive to IR. This filter has a pale pink cast, much like a UV/haze filter, and cuts the spectrum like a knife above 680nm. The cast is easily eliminated by white balancing or basic color correction. Expect to see some HD-size 486 samples at the Schneider Optics booth at NAB. I’m hoping to test one with Adam Wilt shortly thereafter. Stay tuned!

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Wednesday, April 09, 2008

RED Build 15 Flesh Tone Latitude Test (under tungsten light)

In my quest to figure out just how much overexposure latitude I can get out of a RED under tungsten light, I decided to do a test with a flesh tone reference and a RED with build 15 loaded. It turned out to be almost a completely different camera.

Previously I was only able to see two stops of overexposure latitude on a Kodak 18% gray card under tungsten light. That was using build 14. This build seems to yield 3 stops of latitude before clipping flesh tone, which already has more red in it than a gray card. Also, instead of the red channel clipping and causing highlights to turn cyan until the other channels clipped, I see no indication of that at all now. The clipped highlight is very clean and holds color a lot longer than I expected.

On top of that, the DRX highlight recovery tool in Red Alert now seems to cause more problems than it solves. When I used DRX on these clips they turned green, the exact opposite of what they’re supposed to do--which is to take red channel clips that have turned cyan and use the other two unclipped color channels to rebuild detail in the clipped channel, while using the white balance meta data to blend all of that into a neutral highlight.

I don’t know what they did to keep the highlights so clean, but I’d be willing to take this camera into a real world situation now. The only thing that bugs me is that the red channel, which used to be the cleanest color channel by far, now seems very noisy. Maybe that’s a side effect of whatever was done to clean up the highlights.

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Sunday, March 30, 2008

RED results coming soon--stay tuned!

Hi all- I apologize, but I’ve been swamped with work of one sort or another, and when I tried to sit down and start sorting through the latest RED test footage today I couldn’t finish it. I took a nap instead. I must be getting old!

I’ve got three days of shooting this week, and hopefully I’ll be able to pull the footage together and post it by the end of the week. If I were to speculate wildly about the results of the latest round of RED testing, I’d say the following:

The RED definitely has an infrared problem, as previously seen on Reduser.net. We put 7 stops of ND on the lens and saw very severe magenta color shifts on black cloth due to IR contamination. Apparently if the ratio of visible light to infrared becomes too low the RED sees the IR quite easily. I understand that at least one filter manufacturer is currently working on the problem.

We tested build 15, which seems very different to build 14. On build 14 we saw severe problems with red clipping under tungsten light that turned highlights cyan and required highlight recovery work in REDCine and REDAlert to bring back highlight detail. On build 15 it seems that a lot has been done internally to eliminate this problem: the camera seems to hold highlights vastly better under tungsten light, and highlight recovery actually seems to make things slightly worse. There’s obviously something different going on in the camera with this build.

I think there’s some additional processing going on in there, particularly with the red channel. It’s interesting to note that build 14 saw the red channel being the quietest, with green second and blue the noisiest. Now green is the quietest (although still fairly noisy), with red being noisier and blue about the same. Something seems to have happened to the red gain. Also, preliminary histogram examination shows red rolling off around clip instead of hard clipping, which is interesting.

It’s a completely different camera now. I hope to post some build 14 and 15 comparisons and more data later in the week. Stay tuned.

Thanks, as always, to camera guru Adam Wilt for his help and photos. Also thanks to DP Alan Hereford, DP-in-training Ted Allen, and video engineer/co-owner Jay Farrington of Chater Camera (chatercamera.com).

I’ve also got a new showreel coming together, so I suspect I’ll have a lot to say about that process at some point.

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Monday, March 24, 2008

RED: Not a vampire camera at all. It loves daylight!

I’ve now had independent confirmation from a couple of people who watched my RED build 14 exposure tests and have had great luck treating their RED as a daylight film stock. Apparently clipped highlights are significantly less of a problem and noise in the shadows drops way down. It’s a much smoother look.

If you haven’t had a chance to test your RED before shooting to see how well you can recover clipped highlights, it might be a good idea to go HMI or daylight if at all possible. I’m hoping to test recovering clipped highlights and blue filtration by the end of the week, so stay tuned.

Meanwhile, look back a couple of posts in this blog if you need to learn how to recover clipped highlights in Red Alert, and remember that the same control in Red Cine, called “highlight,” does work--but you need to “jiggle” or double-click another control before the new value takes effect. That is slated to be corrected in the next build.

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