I know that many of my readers like to shoot log. One of the most common terms used around shooting log is “shooting flat”. Lets take a look at that term and think about what it actually means.
One description of a flat image might be – “An image with low contrast”. Certainly an image with low contrast can be considered flat.
Once upon a time shooting flat meant lighting a scene so that there was very little contrast. The background in an interview might be quite well lit. You would avoid deep shadows or strong highlights. This was done because cameras had very limited dynamic ranges. These flat images of low contrast scenes could then have the contrast boosted in post production to make them look better.
8 years ago, with the advent of DSLR cameras that could shoot with film like depths of field it became fashionable to shoot flat because digital film cameras when shooting using log produced an image that looks flat when viewed on a conventional TV or monitor.
But lets think about that for a moment. A typical digital cinema camera can capture 14 stops of dynamic range. A scene with 14 stops of dynamic range contains a huge contrast range, perhaps a brilliant bright sky and deep shadows, you can possibly describe the capture a scene with 14 stops of dynamic range as “flat”?
The answer is you can’t – or at least you shouldn’t because the recording isn’t flat. The dynamic range that most digital cinema cameras can capture is not flat, not at all.
The problem is that a normal TV or video monitor can’t show a very big dynamic range. A conventional TV can only show around 6 stops. If you take a log video signal with a 14 stop image and try to show that on a 6 stop screen you will be squashing the highlights and shadows closer together, so the highlight that was at +14 stops in the scene and is recorded at 100%, gets pushed closer to the deepest shadow in the scene that is recorded at 1%.
On a normal 6 stop TV the 100% recording level is shown at +6 stops while the deepest shadow will be at 1%, so now the 14 stop recording is being shown with only 6 stops between the deepest black and the brightest highlight. Instead of the highlight being dazzlingly bright it’s now just a bright white and not all that much brighter than the shadows. As a result the image on the screen looks all wrong, nothing like what you recorded and it appears to be “flat”.
BUT THE DATA IN THE FILE IS NOT FLAT – that recording contains a high contrast, 14 stop image – it’s the inability of the TV or monitor to show it correctly that makes it look wrong, not that you have shot flat.
In the early days of DSLR shooting many DSLR shooters decided to mimic the way the image from a digital cinema camera looks flat on a normal TV, perhaps in the miss-guided belief that a flat image must always have a greater dynamic range. This definitely isn’t always the case. I can take any regular dynamic range image and make it look flat by reducing the contrast, raising the blacks a bit, shifting the gamma perhaps, that’s easy. But that doesn’t increase the dynamic range that is captured. Changing the capture range of a camera typically requires fundamental changes to the way it operates rather than simple tweaks to the basic picture settings.
So we went through a period where shooting a flat looking image with a DSLR was the trendy way to shoot because on a normal TV or monitor the image recorded is reminiscent of the image from a true digital cinema camera shooting log, even though in practice the “flat look” was often damaging the image rather than improving it.
Now there are many digital cinema cameras that can capture a very big dynamic range using log encoding and these images look washed out and flat on a normal monitor or TV because of the miss-match between the camera and the monitor, not because the captured scene is flat. But we still call this shooting flat (wrong)!
Why? In many cases people like to leave the image this way as they like this “incorrect” look. Flat is trendy, it’s fashionable, at least to those inside the TV and Video production world. I’m not sure that the wider general audience really understands why their pictures look washed out.
If you have a monitor with high dynamic range display capabilities such as a Atomos Shogun Flame or Inferno, that can show a large dynamic range then you’ll know that if you feed it log and set the display range to HDR and choose the right gamma curve, the picture on the screen is no longer flat, it’s bright and contrasty. This isn’t a LUT or any other cheat. The monitor is simply showing the image with a range much closer to the capture range and now it looks right again.
So next time you use the term “shooting Flat” think very carefully about what it actually means and whether you are really shooting flat or whether it’s simply a case of using the wrong monitor. Using words or terms like this incorrectly causes all kinds of problems. For example most people think that log footage is flat and that that’s how it’s supposed to look. But it isn’t flat and it’s not supposed to look flat, we are just using the wrong monitors!
4 thoughts on “Shooting Flat – No it’s not!”
Perhaps “straight” (gamma) might be a better term Alister.
Or tell it how it is – “shooting log”?
Log recording reminds me of the “compander” tecnique in storing or tansmitting a waveform signal. The idea goes; “Compress” a wave at 2:1 ratio then BOOST its level and store or transmit it. Then “expand” it at the exact opposite amount on the playout side with a 1:2 ratio. (The polar oposite of the encode ratio) DBX noise reduction was spectacular at this on reel to reel tapes. This made the wave sound very “flat” with little dynamic range. On the playback, the expander would shove the tape hiss and noise floor WAY down, restore the dynamic range deliver a fantastic signal to noise ratio that “tape” could never deliver without “companding”
Log is a similar idea. “Compress” the gamma at a ratio…expose to the right, take in ALL the light you can…then later “expand” (aka contrast) the wave in post back to its original hi dynamic range pre-compressed value.
It really is the classic “compander” concept in wave form processing, storage and transmission. Its how you fit 90+db signal to noise ratio onto a tape that can only hold 50db. Or…in video, 14 stops into a 6 stop rec709 gamma curve.
No, it’s the opposite of a compander.
A audio compander works by reducing the dynamic range of an audio signal by Compressing the dynamic range by boosting the quieter parts of the signal before they are transmitted or encoded. This way the quiet bits are not swamped by any noise. Then at the other end the dynamic range is expanded again by reducing the quiet bits back to their original level, reducing the level also reduces any noise, improving both SNR and Dynamic range.
Log is not reducing or changing the dynamic range in order for it to be later compressed or expanded. It is simply using a different range of code values to record it than are used for conventional TV to allow a bigger range to be recorded in a conventional 10 bit codec. Then in post production the code values are converted to the correct range for viewing, not expanded, not compressed – just as they came from the camera. If you don’t convert the code values to the monitors expected values then the image will look wrong. Use the right monitor and the pictures will look right simply because there is then no change to the contrast or dynamic range. Log encoding definitely does not improve the SNR as a compander does and it definitely is not a way to record 14 stops in a 6 stop gamma curve. It is a totally different type of gamma curve to 709 and that’s why it looks wrong on a 709 TV or monitor. If anything using Log will result in a poorer SNR than using a linear recording. A compander should improve the SNR.