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Sunday, April 26, 2015

••◊ Lavaliere Versus Shotgun Microphones

A colleague and I were talking about the what should go in his production kit next.  He suggested a Sennheiser 416 shotgun microphone, to which I replied that he should really get a wireless lav kit.  The reason being is that he's a one man band corporate video guy and doesn't have a sound mixer with him.  Shotgun mics really need to be used in an echo-free environment with the little or no background noise.  A lavalier microphone isolates a speaker from the background and doesn't require a sound mixer to follow the speaker with the boom pole.
 
Two weeks ago I was at NAB and recorded a number of interviews for Video Gear.  I had my friend's suggested combo: Channel 1 = lav, Channel 2 = shotgun microphone thinking the same thing he was.  I would try to use the shotgun a backup if something went wrong with the lav, because wireless audio isn't perfect either.  Below is a short video with the results

video

As you can hear, the shotgun microphone audio was pretty much worthless at 6 feet from the subject.  Now this isn't to say that a shotgun microphone is worthless.  It just says that there are optimal tools for different situations.  If I would have had a sound mixer with a boom pole we could have gotten really good results by placing the shotgun microphone much closer.  The lavaliere microphone already has this advantage because it's pinned to his collar.

My guess is that my friend will pickup a used wireless lav kit off Ebay and be much better off. 

Friday, April 17, 2015

••◊ The Color Rendering Index and Video Lights

There seems to be a lot of confusion about what lights actually produce good color now days, along with a lot of marketing un-"truthiness" from vendors.  So Dom and I set out to make a video that talks about how video lights actually render color with supporting measurements.  The color rendering index is really a comparison between how colors are rendered by natural sources versus the video light.  We could have gone into black body radiators and Planckian Locus, but I think that would have muddied our intent. 

There is one huge caveat to making a video like this: You can't assume that a certain technology always performs good or bad.  For instance, we measured Fiilex LED lights and they consistently have good color rendering, in measurement and real world use (yes, we actually use them too).  I would personally trust them to produce nice color on camera in most situations.  Another un-named brand of LED light that's in the shop has horrible color rendering and I wouldn't use it if someone held a gun to my head.  I would advise you to do your own evaluation before trusting the marketing numbers.  However, some vendors are very truthful.  Using a C-700 spectrometer I had on loan from Sekonic, we measured great performance on the Cineo TruColor HS at NAB earlier this week and it measured exactly as the vendor stated.  The point of all this is don't make assumptions based on one brand.  We didn't intend the video to make that statement.

I also made this video because I certain number of my friends don't understand why video lights cost any more than hardware store bulbs...then they wonder why they have to constantly tweak color in post to make it look "good enough."  The video delves into that too.  Needless to say, when it comes to LED and fluorescent lights, my advice is to stick to the professional products. 



Sunday, April 12, 2015

••◊ Video Lighting Diffusion Tutorial

I've been meaning to post this for a while now, but I've been lazy/too busy.  Dom and I produced a video showing the various attributes of video lighting diffusion.  I hope you find this useful.  It seems to be one of our more popular videos.




Monday, March 23, 2015

••◊ Review of the Sekonic C-700 Spectrometer

Sekonic sent me a demo unit of the new C-700 Spectrometer.  This meter is meant to help cinematographers, photographers, and gaffers understand where lighting issues occur and help correct them.  What it doesn't do is act as a scientific development tool with download-able spectrum spreadsheets and CIExyz plots, which is more a task for the UPRTek MK350N.  That said, what the Sekonic meter does it does much better than any other color meter tool I've seen before.


The meter is laid out like you would expect from a Sekonic product with the rotating integrating sphere at the top of the unit.  Like their new exposure meters the C-700 features a touch screen that will feel familiar to anyone with a smart phone.  On the left side of the unit there are two buttons: On and Memory.  To turn off the meter you have to press the On button for more than one second.  The memory button can save a measurement to a named file if you press it directly after taking a measurement.  This allows you to save the measurement data to a PC later via the C-700 Utility software.

As with any of the Sekonic meters, the measurement button is on the right side; appropriate for right-hander's thumbs. (second picture below)

As you may notice in the third picture below, the integrating sphere has three click-stop settings: dark calibration (bottom), ambient light (middle), and bright light/flash (top).  When you turn on the meter it has to be set in the dark calibration click stop so the meter can calibrate.  In most cases you'll use the ambient light setting when taking measurements.  If you use the bright setting with video lights it will take significantly longer to do the measurement.  The bright setting is mainly for flash photography.

Speaking of flash photography, there are two ports on the bottom of the unit.  The PC sync port can be used to take measurements with photographic flashes and the USB port is used to connect to a PC and download spectral measurements, perform firmware updates, and change meter settings.

The "hidden" black button at the bottom front of the unit is the home button, just like on a smart phone.





There is a wide range of lighting analysis tools built into the C-700 with the main focus being to help you diagnose color problems and correct them.  I didn't show the home screen below, but you'll be able to access any of these tools by tapping on the appropriate icon on the home screen.  The icon is shown the upper right corner of each of the tools.

In the first picture below you'll see a text analysis of the light.  Here I measured a light that measured a CCT of 3247K, 121 foot-candles, and a color rendering average of 95.8.  This was measured from late day golden sun entering my living room window.

In the second picture below from the spectrum analysis tool you see most of the same data, but with the spectrum plotted.  This can tell you about any problems due to missing parts of the spectrum, as common with fluorescent and LED lights.

The third picture shows how you can actually compare spectrums from a previously saved measurement.  So if you really want to fine tune a gel or match light intensity you can with this tool.

The fourth picture below shows the color rendering rating of 15 colors.  This measurement is generally associated with a CRI rating for the light.  Because this graph shows the rendering rating of each of the colors it's easy to spot problems with the color rendering of a light fixture.  We'll see an example of that later in this article.

As I mentioned previously, the real power of this meter is the ability to find and correct lighting problems.  The fifth and sixth picture below show the tools for adding a camera filter or lighting filter, respectively.  In the camera filter correction tool you can see that the light is measuring 3247K and I input a target color temperature of 5000K.  The meter is recommending that I use a Lee 80C and 82A camera correction filters to get the color temperature back to 5000K in the camera.  This would have been a more common method in the days of shooting actual film that is only available in "tungsten" or "daylight" balance. 

Likewise, in the lighting filter tool I measured a CCT of 5548K and set a target CCT of 3200K.  The tool is recommending that I use a Lee 3/4 CTO to get the light to be 3200K - which makes sense.  No more second guessing or messing around the experimental filter and gel combinations.  That's the huge advantage of this meter over an old fashioned color meter that only gives you CCT and +/-green ratings.

The final picture in this series shows the color shift of the samples relative to the target.  This helps you easily identify green/magenta shifts in the light.  The blue/amber axis basically correlates to the CCT difference, so you get that information from all the tools.  In this example it's saying that the target is much, much more blue (5000K) than the measurement (3247K) and has a magenta bias.





 


I'm not going to dwell over all the settings since that's essentially a user manual.  There are three pages of settings, but I want to cover the two most basic features.  First, you can change the LCD back light brightness.  Under normal video lighting I found the "Normal" setting to be adequate.  However if you're out in the sun you won't be able to see the display with this setting.  You'll need to use the "Bright" setting.  Obviously you want to keep the back light setting as low as possible.  The meter is powered off of 2 AA batteries.

The second feature is that you can choose between Lee and Fujifilm camera filters when the meter recommends correction filters.  Having this database built into the meter makes the meter far more advanced than other options.




Here's a measurement example from 3pm sun just outside my house.  I had to take a picture of the meter in the shade since the LCD wouldn't photograph well in the sun.  The color temperature of 5700K and Ra of 98 seems about right. 

The three graphs below are all output from the included C-700 Utility software.  The first graph shows that my target (5000K) is more amber than what I measured (5700K) - makes sense.  The next graph shows the actual spectrum of the sunshine.  The last graph shows how well the sun renders all 15 colors in the CRI plus special colors.  A very high quality light indeed!





Here's another example from early afternoon (2pm) shade.  Ambient sky light is very, very blue and in this case it's more than 9000K, but still is able to render colors well with an Ra of 98+.  The second graph below shows again that the target (5000K) is much more amber and slightly more green than the ambient sky light measurement.




In this last example I wanted to show an LED bulb, since using LED lights has been somewhat problematic for cinematographers.  Instead of showing a picture of the meter here I wanted to show a screen shot of the C-700 Utility software while viewing the "text" tab.  The LED bulb in my living room is rated for 3000K and a claimed CRI of 92.  In the Text tab we can see that the CCT is measuring 2983K, which correlates well.  However the Ra rating is about 83, which is more like what I would expect from a cheap LED bulb. 

The first graph shows that with a CCT of 2900K we aren't seeing any significant green or magenta bias, which is surprising given that this is a common problem with cheap LED bulbs.

The spectrum shows this light as a common blue LED with a phosphor coating, just as we would expect.  Notice how cyan and deep red are missing from the spectrum, unlike a real tungsten bulb.

Now this is where things get interesting.  A lot of lighting vendors make claims about the wonderful nature of "their" LED technology (everyone purchases from the same 4-5 companies).  The last graph below shows the individual rendering ratings for each of the 15 colors.  Notice how the red patch is 21.5?  You sure wouldn't want to do any product shots for a red Ferrari under these lights.  The color of the car would be WAY off.  Notice how violet has a rating of 65.2?  That means no photography of Barney dinosaur toys under these lights.  Using this graph alone you can see where color rendering problems are going to occur.  Even with orange at 77.1 you probably wouldn't want to use these lights for a cooking show that involved carrots and oranges.   ...You get the drift.


 



I'm dreading giving this meter back to Sekonic. It's a good tool to have in my bag for fixing problems.  I'll be directing a video for Video Gear showing the differences in video lights using this meter, so stay tuned for that on their blog.  I hope this overview of features was helpful.  If you have any questions please feel free to leave a comment.

Sunday, March 15, 2015

••◊ Refocus

I've had a lot of foreign experiences lately in film making and this seemed like the appropriate place to share them.  As we all know, Southern California is well known in other parts of the nation for narcissism.  When you get in the groove here you don't notice it as much, because it unfortunately almost becomes a familiar state of being; more so if you're in the film business.

For example, if you tell anyone that's trying to make it in the film/video business you're from San Diego, they won't talk to you.  The reason being is that they can't use you as a connection to forward their career toward greatness.  The person may swear up and down that they'll call you, email you, or whatever...but it will never happen.  You simply aren't someone they can immediately use as a stepping stone into the film business.  I've seen certain filmmakers go as far as putting in big bold letters on their business card, "based in L.A."

The other problematic behavior I commonly encounter is with social media and disingenuous personalities.  It's quite common for people to becomes Facebook friends simply to use as a reference for someone they really want to talk to.  The person may be a smiling, happy friend to your face but they're really thinking how they can get posts about themselves on your Facebook feed so "Producer X" sees it - and, of course, immediately falls in love with them (to quote Mike Myers, "Yeah!  Sure! ...and monkeys might coming flying out of my butt!).  It's like a game of Frogger to try to gather as many high level Facebook friends and social media followers as they can - A game I happily don't participate in.  You know someone is small-time when they still care about such things.

This is the state of being for a large community of insecure people who are still trying to figure out a way to "make it" - whatever that means.  My alternative proposal is to actually do good work.  People love great content.  I see way too may people chasing nepotism when they should be polishing their skills and doing hard work.  Malcolm Gladwell's 10,000 hour rule still applies.

So this led me to some thoughts on how to refocus myself so I don't become one of the dream chasing, fake personality, L.A. Borg.
  • Try to work with people I enjoy spending time with.  These are people I know in real life and I know they have my back when things don't go as planned.
  • Have adventures that I wouldn't normally have if I wasn't a filmmaker.
  • Chase better art.  Concentrate on the skills, craft, and doing good work; work I can be proud of.
...but if that doesn't work out, feel free to still follow my blog.

Saturday, February 28, 2015

••◊ Color Correcting Footage From The Blackmagic Design Pocket Camera

My friend David recently purchased a Blackmagic Design Pocket Camera.  It's a rather minimalist design with a number of significant quirks, but cheap at $420 on the used market.  He essentially just needed something to record himself and fellow actors practicing lines for his acting class.

What we soon discovered is that the BMPC doesn't have a very complete feature set when it comes to exposure metering.  It has zebras and a histogram, but that's it.  No IRE waveform, no exposure meter...none of the usual fare of a professional video camera.  This made for a difficult situation when filming outdoors with my variable ND filter.  The image from the camera is "flat" in either video and especially film mode.  It also lacks saturation, which makes approximating exposure from the back LCD rather difficult.  (Blackmagic - if you read this PLEASE update your firmware to include a viewing LUT!)

In all fairness, I do own a very nice Sekonic exposure meter.  However most variable ND filters are not marked in stops, much less third of stops.  You get generic 1,2,3...markings that are completely without measure.  So when you're outdoors at ISO 800 (recommended sensitivity) then you're forced to use ND to get a reasonable stop on the lens.  I don't know anyone who carries around a set of screw on fixed ND filters.  I have a nice of set ND's that go in a matte box, but the matte box is easily ten times the size of the camera plus lens!

So my best estimate was to get something that looked kind of close on the back LCD and use a GretagMacbeth color checker chart to set the final exposure in post.  I used the histogram on the back LCD to make sure that my exposure wasn't clipping black or white and the distribution was approximately centered.  This is the same way that you would exposure a Red camera when shooting in raw.  Then I made a final tweak to the variable ND filter to bias the exposure to something that looked a little more correct to my eye.  I knew this would get me in the ballpark for adjustment in post. 

One really great thing about this camera is that it includes two very robust codecs, 12-bit Prores HQ and CinemaDNG raw.  Unlike 8-bit highly compressed footage from a DLSR, adjustments to exposure and color in post are very easy and robust on the BMPC.  These same adjustments would likely destroy footage from my 5D mark II.

So we're starting with something like this...


If you look left to right on the chart, the fourth neutral patch (bottom row, just below yellow) is just just less than middle gray.  I know this because I recently tested it with the Canon gammas in my last blog post.  So adjusting the mid tones to have this particular patch just below middle gray should get my exposure approximately corrected.

The first thing I'm going to do is put a four point garbage matte around the neutral patches and look at the luminance waveform in Premiere.

 

If the picture was properly exposed we would see the fourth patch just below 50 IRE.  In the graph above we see it around 45 IRE, so this tells me the shot was a bit underexposed.  That's pretty easy to fix by bringing up the mid tones with a luma curve.

 
 

For this particular test shot we were using the "video" gamma on the BMPC, which requires a bit less correction than the "film" gamma.  To get a more finalized color I used the fast color corrector effect in Premiere.  The first step is to use the eye dropper in the effect and choose the middle gray patch so that we can establish a good white balance.  Note that I chose 5600K white balance on the camera when recording this shot, so it was already pretty close...just not perfect.  This step also removes the green bias from the variable ND filter.  Then I added about 40% more saturation to the image to get the skin tones where they look natural to me.  Depending on your taste, this may be anywhere from 30-60%.  In "film" gamma it was more like 210-230%, depending on the look you're after. 

The great thing is that with such robust codecs it's not a destructive adjustment.  It's like Blackmagic Design, developers of Davinci Resolve color grading software, want you to do color grading.  Hmmmm...  The downside of this is that you MUST do color correction on all your footage to get it to look decent.  There is no easy-to-use baked-in "look" on this camera.  David is an engineer by training, so he probably likes that characteristic of his toy.


One final step I do is take a look at the highlights and shadows and make small adjustments to them using the luma curve.  This is just for personal taste and not a step that's required.  Often these are very, very minor adjustments.  In this case I want to back off the highlights just a bit to give the pictures a more "filmic" highlight roll off.  The only place you'll probably see the difference here is in the sky reflection in the window.  The shadows look normal to me so there's no need to correct them.

 

Before I conclude this post I just want to point out that what I was trying to do here was color correct the footage, NOT color grade.  That's a whole advanced topic for which I'm not an expert.  I think of color correction as more of a technical process and color grading as an intentional artistic process that requires experience and technical know-how.

If you have any questions feel free to leave a comment.

Sunday, February 22, 2015

••◊ C-log and S-log: Why On 8-bit Cameras?

A lot of the people I congregate with in my small film maker world would easily be described as "low end."  They can afford 8-bit beginner or mid-range cameras and dream of shoots with the Alexa.  One issue I constantly run into is that the camera manufacturers put log gamma curves into their cameras - on 8-bit cameras - and low end folks I work with think this makes their camera just as good as the high end cameras.  Reality is a little different and I'll explain with some simple math.

My two most recent examples are C-log on the Canon C100 and S-log on the Sony A7S.  Let's start with Canon.


In the best case C-log has 5.3 stops above middle gray and 6.7 stops below middle gray, as shown on the picture above.  I stole the picture above from Canon's white paper site on C-log.  From my previous article I measured middle gray on C-log somewhere close to 32IRE.

Now this is going to involve some basic math - and I know videographers generally don't like math.  Just stay with me.  An 8-bit camera produces 256 levels of gray, measured as 0-255.  That same 8-bit level can be measured as somewhere between 0-109IRE.  Doing the algebra here, 32 IRE equals 76 8-bit counts.  That means that the 6.7 stops below middle gray in C-log is represented by 76 counts (i.e. 0-75).  The 5.3 stops above middle gray is represented by the remaining 180 counts.


Doesn't that seem backward that the majority of the dynamic range is represented by 76 counts, while the minority of the dynamic range is represented by 180 counts?  This only gets worse when you decrease the ISO.  For instance, looking at the picture above you can see that at ISO 320 or ISO 400 it's nearly 2/3rd's of the dynamic range that is represented by 76 counts, whereas the remaining third is represented by 180 8-bit counts!

The same is true of S-log on the Sony 8-bit cameras, such as the A7S.  In their case they have Slog-2, which places middle gray at 32 IRE again, with 6 stops above middle gray and 8 stops below middle gray.  So the shadows get 76 counts to represent 8 stops - that's almost the entire dynamic range of a Canon DSLR!

The thing is that these log curves were really designed to work on 10-bit cameras.  In that case you have 300 counts (i.e. greater than an 8-bit range) below 32 IRE.  Stretching the shadow range in post doesn't seem like such a big concern when you start with 10-bits (0-1023).  It's the camera manufacturers' marketing folks that listened to all the low end folks and probably thought they would sell more cameras if they had a box spec that the camera supported a high end feature, like log gamma curves.

The other two issues I usually warn people about is that you need a monitor that supports a LUT in order to see what the final image might look like after color grading.  That's usually not cheap ($2k+).  Plus you need someone that knows how to properly expose (experienced DP) and color correct (experienced DIT) footage shot with a log gamma curve.  If you're eye glaze over while reading about IRE levels, you shouldn't use log gamma curves!  Don't understand vectorscopes or luminance waveforms?...DO NOT use log gamma curves!...Don't use a light meter or know how to measure contrast while lighting - DO NOT USE LOG GAMMA CURVES.  There's a reason log gamma curves are for higher end professionals. 

That said, it's nice to believe for a little while that a low-end 8-bit camera has the same features as a higher end professional camera.  It's almost like those kids who put fancy wheels and a loud muffler on their Honda Civic car and think it's now a sports car.

I color graded some footage off the Blackmagic Pocket Camera yesterday.  Let me tell you; 12-bits makes a huge difference!  What we were doing with that footage would have destroyed an 8-bit capture - and it looked great in the end.  More on that later.