“Film Look” – More on Linear / Log Gamma Curves

I’ve written before on this subject here: Demystifying color bit depth, dynamic range and linear/logarithmic scales but here’s a few more notes on light, and log vs linear gamma curves, as it is one of the most important things you can understand in digital cinema acquisition and post, and it can be confusing for the uninitiated.

Why Light is Linear

Basically if you double the energy emitted from a light source, and the distance from that light source stays constant, the light intensity at that point will also double. Easy right?

Why Light is Not Linear – The Inverse Square Rule

Imagine a single light source in a massive dark room. Standing right next to the light, you’ll experience the highest light intensity possible. Moving to the far end of the room, you’ll experience the least intensity in the room, because the light intensity diminishes over distance.

However, it doesn’t diminish linearly as distance increases. If you stand half way between the light source and the far end of the room, the light won’t be half as bright; it will actually be approximately a quarter as intense. The light intensity is inversely proportional to the square of the distance from the light source.

In photography and cinematography brightness or light intensity is often measured in f-stops as it relates to exposure. F-stops are a unit used to quantify ratios of light, or exposure. Each added stop represents an increase in light intensity by a factor of two, each increased stop is a doubling of light intensity, or exposure. A decrease of one stop is a halving of light intensity or exposure.

From Wikipedia:

The f-stop scale is an approximately geometric sequence of numbers that corresponds to the sequence of the powers of the square root of 2:   f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32, f/45, f/64, f/90, f/128, etc.

You don’t need to understand the math, just what it means. So f/2 represents double the light intensity of f/2.8 but half the the light intensity of f/1.4.

Human Perception is Not Linear

This is the real world physics of light. However, our perception of luminance is quite different and that is important when it comes to how we map real world linear luminance values to perceived brightness. We are more sensitive to small changes in luminance at the low end of the scale than the high end.

The Gamma Curve – Linear vs Log

I found the below descriptions from RyanJuckett.com very useful, he’s speaking in the context of color science as it relates to computer graphics and coding for games but it is a good explanation of the gamma curve nonetheless:

The gamma correction curve is used to convert pixel luminance from a linear scale to an exponential scale. When encoding the final pixel value, the curve is used to gamma compress linear luminance to a gamma corrected value. When decoding a pixel value, the inverse curve is used to gamma expand the value back to linear units.

We don’t perceive the luminance of a color on a linear scale, so this gamma compression actually helps us store more useful information in a limited number of bits per pixel. This nonlinear relationship between linear luminance and the perceived brightness of a color (also known as lightness) is shown below.

Linear Luminance

If we were to store image values on a linear scale, single steps in value would correspond to large steps in lightness on the lower end of the scale and minor steps in lightness at the higher end of the scale. As a result, we would lose a lot of lightness fidelity in dark colors.

Now let’s look at luminance using the sRGB gamma corrected curve.

Gamma Luminance

We now get consistent steps of lightness across all values letting us encode lightness with more fidelity across the entire scale. While this image does show linear lightness (human perception), it should be stressed that we are no longer working with linear luminance (physics).

To go through this one more time, lets use 10 bit values as an example; you have 1024 possible values (including 0) to map input luminosity levels to output values from black to white. So your output range is between 0 (black) and 1023 (white).

A normal idealized gamma curve is actually almost a straight line, and this linear mapping will divide values perfectly evenly between 0 and 1023 across the scale of linear luminance, so the mid point of 512 will be exactly half way between black and white, which is 50% grey right?

Wrong. A value of 512 will actually be about 75% grey. There will be far fewer values mapped to the dark end of the scale than the bright end with linear mapped values.

If you have 1023 possible values to map to luminosity levels, it is a waste of valuable data to spread them perfectly evenly because our perception is not linear, we are more sensitive to changes in the shadows and mid-tones than in highlights.

A logarithmic gamma curve also serves to better assign data to expanded highlight information from high dynamic range imaging sensors.

This is why a log image viewed without gamma correction will look very flat and washed out.

In the context of the Blackmagic cameras “Film” and “Video” modes, simply put, “Video” mode applies a more linear gamma curve to the image and “Film” mode applies a logarithmic gamma curve preserving the shadows and midtones and expanding the highlights.

Video example

Above, a more linear gamma curve. Video mode.

RAW exampleAbove, a log gamma curve (without gamma correction). Film mode.

I highly recommend reading Understanding Gamma, CineGamma, HyperGamma and S-Log by Alistair Chapman on dvinfo.net

Pimp Your Pocket Cinema Camera – Pt 3 – Canon EF SpeedBooster!

Following on from the last of my Pocket Cinema Camera posts (Pimp Your BMD Pocket Cinema Camera – Pt 2 – Super 35mm in Your Pocket!) where I introduced the Metabones Nikon G to BMPCC SpeedBooster, I now want to introduce the long awaited Canon EF version.

CanonEF_Metabones_Speedbooster

It’s absolutely brilliant. Everybody needs one of these.

Here’s some test shots showing the huge difference the Metabones SpeedBooster makes to the field of view by reducing the sensor crop factor from 3.02 to 1.75 on the Pocket Cinema Camera. Notice the exposure is also brighter using the Speedbooster. The aperture on the lens was T2.8 and wasn’t changed, so the brighter exposure (technically +1 2/3 stops) is from the Speedbooster only.

NOTE: The Metabones SpeedBooster BMPCC – Canon EF adaptor does not work with Canon EF-S lenses, only EF lenses. It does however provide electronic aperture control from the camera to Canon EF lenses.

Below: Without SpeedBooster – using Redrock Micro Livelens MFT to EF adaptor. Lens is a Samyang 24mm at T2.8, 400ASA on Pocket Cinema Camera.

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Below: with Metabones SpeedBooster BMPCC – Canon EF – Lens is the same Samyang 24mm at T2.8, 400ASA on Pocket Cinema Camera.Metabone_Speedbooster_CanonEF

 

The subject for these test shots by the way is the lovely Avid S6 Control Surface which just happened to be laying around :P

Check out the previous posts:

Pimp Your Pocket Cinema Camera – Pt1 – Power in Your Pocket!
Pimp Your Pocket Cinema Camera – Pt2 – Super 35mm in Your Pocket!

Blackmagic Camera References – Data Rates, Recording Times, Shutter Angle

Below you’ll find some useful references I compiled as part of a larger FAQ reference I am working on for the cameras. I have not listed data rates for all the frame rates, just for 25fps to give a rough idea.

Data Rates – Comparative data rates for Prores are given below. (Mb = Megabit, not Megabyte (MB)… there are 8 bits in a byte, so divide these numbers by 8 if you want MB/sec)

1920 x 1080 @25fps 3840 x 2160 @25fps
ProRes 422 HQ 184Mb/sec 737Mb/sec
ProRes 422 122Mb/sec 492Mb/sec
ProRes 422 LT 85Mb/sec 342Mb/sec
ProRes 422 Proxy 38Mb/sec 151Mb/sec 

Recording Times – Below you can find recording times for each camera and format.

For the Cinema Camera:
–       480 GB SSD, recording RAW = approximately 65 minutes
–       480 GB SSD, recording ProRes 422 HQ = approximately 5.9 hours
–       480 GB SSD, recording ProRes 422 = approximately 9 hours
–       480 GB SSD, recording ProRes 422 LT = approximately 12.8 hours
–       480 GB SSD, recording ProRes 422 Proxy = approximately 28.8 hours

For the Production Camera 4K:
–       480 GB SSD, recording CinemaDNG RAW = approximately 35 minutes
–       480 GB SSD, recording ProRes 422 HQ = approximately 89 minutes
–       480 GB SSD, recording ProRes 422 = approximately 2.2 hours
–       480 GB SSD, recording ProRes 422 LT = approximately 3.2 hours
–       480 GB SSD, recording ProRes 422 Proxy = approximately 7.2 hours

For the Pocket Cinema Camera:
–       64 GB card, recording RAW = approximately 15 minutes
–       64 GB card, recording ProRes 422 HQ = approximately 35-40 minutes
–       64 GB card, recording ProRes 422 = approximately 70 minutes
–       64 GB card, recording ProRes 422 LT = approximately 1.7 hours
–       64 GB card, recording ProRes 422 Proxy = approximately 3.3 hours

Native ISO – Below you can find the native ISO for each camera.

Pocket Cinema Camera – ISO 800
Cinema Camera – ISO 800
Production Camera 4K – ISO 400

Shutter Angle to Shutter Speed Conversion – Below you can find the shutter speed in 1/x sec. For example… 25 frames per second (fps) on 180 degree shutter angle = 1/50th sec shutter speed.

Shutter Speed (1/x sec) at the below frame rates (fps)
Shutter Angle (Degrees) 23.98fps 24fps 25fps 29.97fps 30fps
45 191.84 192 200 239.76 240
90 95.92 96 100 119.88 120
108 79.93 80 83.33 99.90 100
144 59.95 60 62.50 74.93 75
172.8 49.96 50 52.08 62.44 62.50
180 47.96 48 50 59.94 60
216 39.97 40 41.67 49.95 50
270 31.97 32 33.30 39.96 40
324 26.64 26.67 27.78 33.30 33.33
360 23.98 24 25 29.97 30

 

Unboxing the Blackmagic Studio Camera

Today was unboxing day and since yesterday’s post had no images, I thought I’d share these with you today.

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Very impressed with the finish and build quality, the body is die-cast magnesium alloy and is really almost feather light. The four pin XLR power is a great move on this camera but what blows me away is a studio camera with fiber connectivity at this price point. It’s just nuts.

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Look! XLR’s! :D

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Big backlit buttons for key functions and menu navigation.

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Not at all a studio lens, but to throw a image on the sensor the Voightlander Nokton 25mm f/0.95 was what I had laying around. I look forward to testing with an active Panasonic Lumix zoom lens also.

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The 10″ full HD viewfinder is very crisp and clear, very bright. After seeing it I actually wish the Cinema Camera had this screen, even if it meant a bigger body… well, URSA does! It is very reflective though which may bother some users.

So far, very impressed with this camera. I think we will see much more coming for this camera in the months ahead, including possibly a viable powered and active B4 adaptor. MTF Services already make a powered B4 to Sony EX3 adaptor, as well as a B4 to MFT adaptor for super 16mm sensors. I wonder what it would take to combine the two. Such a solution would take this camera to a whole new level with real support for ENG zoom lenses and remote control.

More to come! Watch this space!

Blackmagic Design – Rebels with a Cause

Today the first Blackmagic Studio Cameras landed in Dubai. In my research leading up to this day, and the inevitable need to support and answer a ton of pre-sales questions about this new animal, I’ve discovered a few important “limitations” with the much anticipated Blackmagic Studio Camera.

Whether these “limitations” are perceived or real is the question that is really on my mind. I believe Blackmagic are breaking new ground here and that will always be met with resistance from the guardians and defenders of the established norms.

This is a camera that is not likely to please everyone in the professional broadcast and studio establishment, but may appeal to new and open-minded low budget users crossing over that are willing to overlook a few things, or more likely than not won’t miss them in the first place.

1. The only way to mount a proper ENG zoom lens is with a dumb MFT to B4 adaptor. That means no remote lens control is possible through the camera. Full stop.

Due to the sensor size being larger than that of a 2/3” broadcast camera sensor, only ENG zoom lenses with a 2x extender engaged can be used. This has always been the case, as with the Cinema Camera and a MFT to B4 adaptor, but I don’t consider this a problem necessarily, it’s just a fact.

Remote color balancing and adjustment is of course still possible through the ATEM, just no remote iris / zoom / focus control with a ENG lens.

For many established studios wishing to use a Blackmagic Studio Camera / ATEM combination with professional ENG zoom lenses to replace their current setup, this lack of remote lens control will be a complete deal breaker.

2. So it seems that if full remote lens control is desired, only an active MFT lens with servo zoom will work. That’s basically only one lens. The Panasonic LUMIX® G X VARIO PZ 45-175mm / F4.0-5.6 ASPH. However I don’t think it is a perfectly parfocal lens (able to maintain focus throughout zoom range) although if you know better, please correct me if I’m wrong, and it is not constant aperture. http://shop.panasonic.com/shop/model/H-PS45175K

The hardened old-school professionals who haven’t switched off at point 1, will have left the room whispering (or shouting) four letter expletives at point 2.

I just don’t think those people are the intended target market.

3. Apparently the “interlaced” outputs are not really interlaced but somehow pseudo interlaced from an internally progressive source. Now I haven’t had a chance to look into this yet and am happy to be wrong, but it would make sense seeing as the read-out from the sensor is most likely progressive as with all the other Blackmagic cameras. I anticipate this may be problematic for some expecting a true interlaced output. I don’t know whether this is technically then PsF (Progressive Segmented Frame) or what.

4. The software color and camera control will not be familiar for anyone used to hardware CCU controls. God forbid anyone try anything new.

Therefore my initial thoughts are that this was never intended to be a replacement solution for the established broadcast market. It’s a new system, a new way of running a multi-cam live production and a extremely cost effective entry point for a brand new market.

Some accuse Blackmagic of completely ignoring the established existing requirements of studio production, arguing that if they hadn’t they would have made a Studio Camera with a 2/3” sensor, B4 mount and lens control… which they did… the URSA Broadcast Camera. However I don’t believe this is the case. I see a lot of innovation here and in my opinion they are going after a less experienced, new market of crossover DSLR shooters and cinematographers that are happy to control their own lens at the camera, and were simply wishing for a way to feed multiple sources to a switcher and color balance multiple cameras centrally. That makes sense to me and for that Blackmagic have provided a excellent beginning to end solution at a ridiculously affordable price.

I’m not sure they ever intended to make the ENG purists happy with the Studio Camera… Blackmagic are doing something new here, and I see a deepening blend between EFP / Cinema and ENG / live production.

Pimp Your BMD Pocket Cinema Camera – Pt 2 – Super 35mm in Your Pocket!

In my previous post last week I set out to introduce you to the minimalist approach to equipping the Blackmagic Pocket Cinema Camera for shooting from the hip in any situation as quickly as you can grab your camera, frame your shot and hit record.

Many would love it if Blackmagic had shoehorned a larger super 35mm sensor into the pocket camera, but for whatever reasons they didn’t, and it’s a lovely super 16mm format camera. No amount of wishing can change that fact. However, for those intending to shoot with 35mm format lenses and for lovers of the 35mm ultra shallow depth of field that is considered de-facto standard for any respectable digital cinema camera, Metabones has come to your rescue with the latest Speedbooster for Nikon F lenses.

Metabones have released two versions each with optics tailored to reduce the sensor crop as much as possible for the BMC and BMPCC respectively. By optically reducing the image circle of the larger 35mm format lens to better match the smaller sensor, the light is also intensified giving you 1 2/3 extra stops (on the BMPCC version) on any given lens.

This actually turns the pocket camera’s smaller sensor from what some might consider a disadvantage into a huge advantage over full frame cinema cameras in that you’ve got more than a stop and a half brighter exposure plus a 35mm aesthetic which is closer to the un-cropped field of view using 35mm lenses.

So the BMD Pocket Cinema Camera with the Metabones Speedbooster – BMPCC Version gives you the smallest (close-to) 35mm digital cinema camera solution available. The adaptor reduces sensor crop factor from 2.88x to 1.75x and makes any lens 0.58x wider. A 50mm f/1.2 becomes a 29mm f/0.74!

This can get confusing. To put this back into terms of 35mm equivalency… a straight-up Nikon F to MFT lens mount adaptor with no reduction in sensor crop will mean a 50mm lens with the BMPCC’s 2.88x sensor crop gives you the equivalent field of view of 144mm in the full frame 35mm sensor world. With the BMPCC Speedbooster, the crop factor reduces to 1.75x so your 50mm lens looks like what you’d expect of a 87.5mm on a full frame camera… or from a 29mm lens on a straight mount adaptor… only 1 2/3 stops faster :) Got it? Good!

F0.74 – The new Metabones Speed Booster – BMCC & BMPCC versions from Andrew Reid on Vimeo.

 

Pimp your BMD Pocket Cinema Camera – Pt 1 – Power in Your Pocket!

I’ve been meaning to do this for ages, so this is the first write-up of a series on the Blackmagic Pocket Cinema Camera (BMPCC) and later the Cinema Camera (BMCC). I hope that these will start to come more regularly now and I can get this blog back up to the old days of 1000+ views a day :)

Also for those of you used to all my RED ramblings, my love of all things Epic has not changed, I’ve just found something else I like in addition, and for many of the same reasons. Blackmagic Design are responsible for some seriously ingenious and innovative products, and so now it’s their turn for a bit (until I get my hands on RED Dragon to review :P)

I also want to say I have my hands on these cameras every day, and interact with others who have been shooting for some time now on the Blackmagic cameras, so everything I’m writing about is real world, no BS feedback and opinion from actual use.

Digital Super 16mm

Super 16mm holds a special place in my heart. A few years ago I could be seen regularly with my clockwork WWII era Russian K3 hanging around my neck and a backpack full of film stock. I’d take the camera all over and shoot whatever was around me that was interesting.

As a result, I was very excited about the idea of a true super 16mm “digital film” camera and Blackmagic Design delivered exactly that. Of course it’s full HD, far cleaner and superior than the K3 I loved so much but it delivers a full 13 stops, records RAW and in post gives you all the latitude and flexibility you could ever want… plus I don’t have to load film in the dark, process anything or wait for telecine transfers. Bonus.

The BMPCC is a revolutionary device, and I know all about the new Digital Bolex, which is all well and good with its global shutter, dual CF card slots, internal SSD and $3300 price tag but Blackmagic Design have put the core essentials of all that in the palm of your hand at $995 (and you can actually have it right now). In my opinion I could care less about the Bolex.

With all that said, I am going to start this series by sharing a ideal minimalistic pocket setup that’s all about getting out there and capturing the world exactly as it is with no fuss, no setup, no excuses.

Very often less is more, and this configuration is about putting serious cinematic power in your pocket, literally. If you are a instagram or iPhone photo junkie like me then having a true full HD digital cinema camera in your pocket at all times opens up a world of creative possibilities.

I will say right now I’m a massive fan of the Voightlander Nokton lenses and the only reason I am not listing a Voightlander in this list is that for this setup I want something as flat as possible. I’ll touch on the Voightlanders again however in a bit.
Blackmagic Design Pocket Cinema Camera

13 stops of 1080p RAW in your hand.

For a camera you want to carry around with you, it’s all about being light and super compact so in this list theres no cage, no external V-mount battery, no handles, no excess weight. Just some extra EL20 batteries and media to carry in a free pocket, one fast medium wide pancake lens and a few filters.

For this recipe you will need:

1 x Blackmagic Design Pocket Cinema Camera
3 x BMD EN-EL20 Battery
1 x Panasonic LUMIX G 20mm f/1.7 II ASPH. Lens
3 x SanDisk Extreme Pro SDXC 64GB Memory Card
1 x Heliopan 58mm Variable ND Filter
1 x Hoya 58mm Circular Polarizer Filter
1 x Hoya 58mm UV Filter
1 x 46mm – 58mm step-up ring

A note on the variable ND, the Heliopan is arguably the sharpest of all the variable ND filters available, but they don’t make a 46mm size. So I would recommend getting whatever size in the range that suits the largest of any other lenses you might want to use and get a step-up ring from 46mm for the pancake. I’ve chosen 58mm because it will fit the Voightlander Nokton 17.5mm and 42.5mm (and 25mm with a step up ring), as well as the fantastic Olympus M. Zuiko Digital ED 75mm f/1.8 and carrying a step-up ring for the smaller lenses is not a big deal.Three batteries and cards should be great for most day outings that you’d carry your camera with you. We’re talking informal, fast, creative shooting here. Great results are all about light, contrast and composition. In this minimal list you’ve got one fixed focal length lens, so be prepared to move to frame your shots. It’s about capturing moments, and being fast enough on your feet to do so.A ultra portable tripod or monopod would work well also if you are willing to carry it. The Miller Air is fantastic and not too heavy on the shoulder. You could even get into carrying a small slider, but if you start down that road the portability and quickness starts to erode and you’re in production mode before you know it with a whole lot of gear on your back to lug around.

Taking this minimalist setup further is as easy as adding some more lenses, and at this point I’ll come back to the Voightlander Nokton lenses.
Voightlander Nokton MFT primes.

Seriously fast! Voightlander Nokton MFT primes at f/0.95.

These lenses deserve a whole write-up on their own. I love them! Available in 14.5mm, 25mm and 42.5mm at a staggering F0.95 they practically see in the dark. While there is some glow in the highlights, or any light sources within your shot when wide open, it’s practically gone at F1.4 and beyond. Needless to say if you want a f/0.95 lens that doesn’t glow, the Leica 50mm Noctilux f/0.95 will set you back $11,000, so I think the Nokton trio at 1/10th the price can be forgiven.
On a side note, some additional fantastic lenses to keep in a small bag or your backpack with you if you wanted some options might be one or more of the following.Olympus M.Zuiko Digital ED 12mm f/2.0
Panasonic Lumix Leica D Summilux 25mm /F1.4 ASPH
Olympus M. Zuiko Digital ED 45mm f/1.8
Olympus M. Zuiko Digital ED 75mm f/1.8You can find many good reviews of these lenses with a quick search.

The Olympus 12mm and Lumix Leica 25mm are also 46mm filter thread size so the same filters in the above list would screw onto these also. The Olympus 45mm I’ve listed has a smaller 37mm filter thread so you would need a step-up ring just for that lens.

The Olympus 75mm may seem like a odd lens to include as it is long (150mm equiv) for a portrait lens but really is a standout fantastic lens. It is a larger lens, with a 58mm filter thread, which is why I chose 58mm filters in the basic list.

Next time I’m going to talk about building a more serious production ready pocket cinema camera featuring the M43 to Nikon Speedbooster by Metabones and some more serious accessories.

I’ve also taken out the pocket cam rigged with the wooden camera PL adaptor and a few Optimos so I’ll touch on shooting with PL glass too.

More fun to come. Thanks for reading.