Tag Archives: slog

Lastolite EzyBalance Calibration Card – Pop-up grey card and 90% white card. Review.

2014-07-15-08.35.54-300x168 Lastolite EzyBalance Calibration Card - Pop-up grey card and 90% white card. Review.
Lastolite EzyBalance pop up grey card.

Fed up with carrying large or bulky grey cards that get bent and creased or get dirty and fade? Why not try one of the great Lastolite pop up grey cards? I have the 30cm 18% grey pop-up grey card and it works really well. When folded it’s only about 12cm across so takes no space at all. It comes in a handy zip up case. This is so much easier to carry and transport than traditional ridged cards. The back of the target is 90% white. Both the grey and white targets appear to be very accurate and the matte surface of the grey card helps eliminate hot spots and reflections. There is a cross hair style focussing target in the center of each side if you need to check focus. They come in different sizes, if you want a larger one there are also 50cm and 75cm versions plus there is even an underwater version. Do note that they come in both 18% and 12% shades of grey. Really handy if shooting with SLog or for setting white balance. If you are working with a video camera you want the 18% grey version, but you may need the 12% version if calibrating a light meter etc. Simple, low cost item that works really well. Recommended!

http://www.lastolite.co.uk/ezybalance-grey-wht-card-03m-lllr1250

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Understanding Sony’s SLog3. It isn’t really noisy.

It’s been brought to my attention that there is a lot of concern about the apparent noise levels when using Sony’s new Slog3 gamma curve. The problem being that when you view the ungraded Slog3 it appears to have more noise in the shadows than Slog2. Many are concerned that this “extra” noise will end up making the final pictures nosier. The reality is that this is not the case, you won’t get any extra noise using Slog3 over Slog2. Because S-Log3 is closer to the log gamma curves used in other cameras many people find that Slog3 is generally easier to grade and work with in post production.

So what’s going on?

Slog3 mimics the Cineon Log curve, a curve that was originally designed, back in the 1980’s to match the density of film stocks. As a result the shadow and low key parts of the scene are shown and recorded at a brighter level than Slog2. S-Log2 was designed from the outset to work with electronic sensors and is optimised for the way an electronic sensor works rather than film. Because the S-Log3 shadow range has more gain than S-log2, the shadows end up a bit brighter than it perhaps they really needs to be and because of the extra gain the noise in the shadows appears to be worse. The noise level might be a bit higher but the important thing, the ratio between wanted picture information and un wanted noise is exactly the same whether in Slog2 or Slog3.

Let me explain:

The signal to noise ratio of a camera is determined predominantly by the sensor itself and how the sensor is read. This is NOT changing between gamma curves.

The other thing that effects the signal to noise ratio is the exposure level, or to be more precise the aperture and how much light falls on the sensor. This should be same for Slog2 and Slog3. So again no change there.

As these two key factors do not change when you switch between Slog2 and slog3, there is no change in the signal to noise ratio between Slog2 and Slog3. It is the ratio between wanted picture information and noise that is important. Not the noise level, but the ratio. What people see when they look at ungraded SLog3 is a higher noise level simply because ALL the signal levels are also higher, both noise and desirable image information. So the ratio between the wanted signal and the noise is actually no different for both Slog2 and Slog3.

Gamma is just gain, nothing more, nothing less, just applied by variable amounts at different levels. In the case of log, the amount of gain decreases as you go further up the curve.

Increasing or decreasing gain does NOT significantly change the signal to noise ratio of a digital camera (or any other digital system). It might make noise more visible if you are amplifying the image more than normal in an underexposure situation where you are using that extra gain to compensate for not enough light. But the ratio between the dark object and the noise does not change, it’s just that as you have made the dark object brighter by adding gain, you have also made the noise brighter by the same amount, so the noise also becomes brighter and thus more obvious.

Lets take a look at some Math. I’ll keep it very simple, I promise!

Just for a moment to keep things simple, lets say some camera has a signal to noise ratio of 3:1 (SNR is normally measured in db, but I’m going to keep things really simple here).

So, from the sensor if my picture signal is 3 then my noise will be 1.

If I apply Gamma Curve “A” which has 2x gain then my picture becomes 6 and my noise becomes 2. The SNR is 6:2 = 3:1

If I apply Gamma Curve “B” which has 3x gain then my picture becomes 9 and my noise becomes 3. The SNR is 9:3 = 3:1 so no change to the ratio, but the noise is now 3 with gamma B compared to  Gamma A where it is 2, so the gamma B image will appear at first glance to be noisier.

Now we take those imaginary clips in to post production:

In post we want to grade the shots so that we end up with the same brightness of image, so lets say our target level after grading is 12.

For the gamma “A” signal we need to add 3x gain to take 6 to 18. As a result the noise now becomes 6 (3 x 2 = 6).

For the gamma “B” signal (our noisy looking one) we need to use  less gain in post, only 2x gain, to take 9  to 18. When we apply 2x gain our noise for gamma B becomes 6 (2 x 3 = 6).

Notice anything? In both cases the noise in the final image is exactly the same, in both cases the final image level is 18 and the final noise level is 6, even though the two recordings started at different levels with one appearing noisier than the other.

OK, so that’s the theory, what about in practice?

Take a look at the images below. These are 400% crops from larger frames. Identical exposure, workflow and processing for each. You will see the original Slog2 and SLog3 plus the Slog 2 and Slog 3 after applying the LC-709 LUT to each in Sony’s raw viewer. Nothing else has been done to the clips. You can “see” more noise in the raised shadows in the untouched SLog3, but after applying the LUTs the noise levels are the same. This is because the Signal to Noise ratio of both curves is the same and after adding the LUT’s the total gain applied (camera gain + LUT gain) to get the same output levels is the same.

Slog2-400 Understanding Sony's SLog3. It isn't really noisy.
Slog3-400 Understanding Sony's SLog3. It isn't really noisy.Slog2-to-709-400 Understanding Sony's SLog3. It isn't really noisy.Slog3-to-709-400 Understanding Sony's SLog3. It isn't really noisy.

It’s interesting to note in these frame grabs that you can actually see that in fact the S-Log3 final image looks if anything a touch less noisy. The bobbles and the edge of the picture frame look better in the Slog3 in my opinion. This is probably because the S-Log3 recording uses very slightly higher levels in the shadow areas and this helps reduce compression artefacts.

The best way to alter the SNR of a typical video system (other than through electronic noise reduction) is by changing the exposure, which is why EI (Exposure Index) and exposure offsets are so important and so effective.

Slog3 has a near straight line curve above middle grey. This means that in post production it’s easier to grade as adjustments to one part of the image will have a similar effect to other parts of the image. It’s also very, very close to Cineon and to Arri Log C and in many cases LUT and grades designed for these gammas will also work pretty well with SLog3.

The down side to Slog3?

Very few really. Fewer data points are recorded for each stop in the brighter parts of the picture and highlight range compared to Slog2. This doesn’t change the dynamic range but if you are using a less than ideal 8 bit codec you may find S-Log2 less prone to banding in the sky or other gradients compared to S-Log3. With a 10 bit recording, in a decent workflow, it makes very little difference.

 

Convergent design Gemini S-Log frame grabs.

Hi all. A very brief post as I’ve just got back to the hotel from a long day at Broadcast India.

I finally found a little bit of time to upload a couple of quick frame grabs from the Gemini. Sorry they are not Tiff’s or the DPX files but time is scarce.

There are 3 frames: The graded S-Log, A Cinegamma 3 grab and the raw S-Log.

The increase in dynamic range over the cinegamma frame is clearly visible in the highlights outside the window as well as on the wall behind the actor.

I have to say I’m liking the Gemini a lot. The firmware is not quite there yet but it’s very, very close with almost daily updates being released. Apart from an initial hiccup (which has now been rectified) the unit has been stable even in the Mumbai heat. It amazes me and everyone else that see’s it that the little 5″ monitor sitting on the handle of my F3 is also a 4:4:4 uncompressed recorder, its so compact compared to all the other alternatives. Being able to apply LUT’s on the Gemini is also very neat.

The screen is super bright and easily viewable in direct sunlight. Im powering both the camera and the Gemini of a single Swit S-8U62 battery which gives me a little over 2 hours from a full charge.

It does generate some pretty big files, so I have been using Adobe Premier to transcode the clips to Apple ProRes 4:4:4 on ingest. This is taking a little longer than I expected, but then I am using a vintage MacBook Pro 3.1 and I guess is a small penalty to pay for the incredible image quality that I’m getting.

Combine all this with the soon to arrive EI-SLog firmware from Sony and it will all only get better and better.

SLog-sample-graded-1024x576 Convergent design Gemini S-Log frame grabs.
S-Log with basic grade applied
CG3-sample-1024x576 Convergent design Gemini S-Log frame grabs.
Same shot but Cinegamma 3
SLog-sample-1024x576 Convergent design Gemini S-Log frame grabs.
Raw S-Log frame grab. Click on image for flu frame.