ISO when shooting RAW

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Brad Ballew

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ISO when shooting RAW

PostTue Apr 02, 2013 10:11 pm

I have heard from a couple of people that your ISO setting in RAW doesn't really effect anything. Since this is my first RAW camera this is a new concept to me. Could someone elaborate a little more on this.. I like to be as familiar with the technical side of things as I can. Is it simply because.. well.. it's RAW and it's going to capture all the info within it's seeable range no matter what the ISO setting?
Brad Ballew
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Michael Beck

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Re: ISO when shooting RAW

PostTue Apr 02, 2013 11:43 pm

You should do some research on RAW, it is a deep topic.

you can start here:
http://en.wikipedia.org/wiki/Raw_image_format
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-Michael Beck
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Dillon McEvoy

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Re: ISO when shooting RAW

PostWed Apr 03, 2013 1:11 am

Shooting at ASA 200 I've noticed produces the cleanest image in RAW
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Aaron Scheiner

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Re: ISO when shooting RAW

PostWed Apr 03, 2013 3:26 pm

The ISO setting on the camera is a representation of the gain settings in effect on the preamps (between the sensor and the ADCs or analog/digital converters). Increasing the gain/ISO causes more of the noise floor to be recorded and can cause highlights to over-expose. It also effectively results in a loss of dynamic range.

Decreasing the ISO/gain will lower the noise floor (cleaner image) but can also cause shadow detail loss. Areas of the sensor can overexpose even if the level doesn't max out the ADCs. The effect of this differs between cameras but ultimately also results in a loss of dynamic range.

Ultimately the best ISO is the native ISO, which would appear to be 800; the manual states that 800 is the "optimum" setting for ISO... implying that it is the native ISO (at which the most amount of dynamic range is preserved).

In short, ISO (or gain) will affect the raw output of the camera, it's more than just metadata.

If someone thinks I'm wrong, say so ;) .

And... that Wikipedia article doesn't talk about ISO or gain at all.

The manual can be found here.
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Frank Glencairn

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Re: ISO when shooting RAW

PostWed Apr 03, 2013 6:28 pm

Come on guys, in raw, ISO is just metadata - everybody knows that.

Only if you set it to 1600, the curve gets mapped a bit different, to prevent noise in the blacks.
But it still is metadata.
http://frankglencairn.wordpress.com/

Set your zebras to 100%, ETTR and you're golden - and NO, you can't use TB as output for an external monitor, and you can't download the footy via TB ether.
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Felix Steinhardt

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Re: ISO when shooting RAW

PostWed Apr 03, 2013 7:15 pm

It´s not the case with DSLRs shooting RAW pictures. There analog gain is applied. I was also confused at first when I heard about the RAW ISO metadata thing on the RED cameras a few years back.
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Aaron Scheiner

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Re: ISO when shooting RAW

PostWed Apr 03, 2013 7:40 pm

Both traditional video cameras (Sony PMW-EX3, Z7, etc.) and Canon DSLRs* use analog gain between the sensor and the ADCs... but it appears that RED cameras have fixed analog gain which means the BMCC is probably also fixed and that means, as Frank said earlier, ISO on the BMCC is purely metadata and has no material effect on the raw output.

I'm learning ;) .

It would be great if I had a camera with which to test this :P .

*
http://shootintheshot.joshsilfen.com/2010/05/13/canon-hd-dslr-native-iso/
http://wiki.magiclantern.fm/userguide "ISO"
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Alain Baars

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Re: ISO when shooting RAW

PostSat Apr 06, 2013 9:41 pm

So I hear two different stories here; one that states that ISO is just metadata (which sounds logical to me), the other one claims that ISO variation gives wider/narrower DR.

What is the right statement and what is the native ISO for the BMCC?

I'm a commercial photographer since 1992 and I know that in that business a lot of people say they 'know' it, when they mean they 'suppose' it.

In other words, I respect everyone's opinion, but I really would like to know what it's really about.
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Aaron Scheiner

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Re: ISO when shooting RAW

PostWed Apr 10, 2013 7:29 pm

So now that I have a BMCC to play with... I tried shooting the same shot with different ISO settings in raw. I then grabbed a DNG from each ISO region and loaded them into Photoshop. On import I clicked "Auto". I then applied -2 from the exposure that the importer chose to get a sense of clipped highlights and in separate set of imports added +2 to the exposure the importer chose to get an idea of grain.

Given that the shots were identical with the exception of ISO on the camera, Photoshop's DNG importer should(?) have exposed the shots so that the output was identical regardless of ISO (assuming analog gain is static).

But this didn't happen.

I couldn't discern any differences between the 400 and 800 ISO shots but there seemed to be a difference between both the 1600 and 400/800 shots and the 200 and 400/800 shots.

This is an experiment, by all means point out flaws in my logic please :P . I don't know the answer to the gain question.

Initial observations (all comparing 200 to 1600) :

The grain in the 200 ISO shots seems to be coarser (and have more grain artifacts).
Highlights seem to clip more at 1600.
In the levels dialog less shadow detail seems to be present in the 200 ISO shot.
In the levels dialog less highlight detail seems to be present in the 200 ISO shot.

That said, the differences are very small.

It would be great, just for clarity, to know whether or not ISO does shift analog gain.

I'll upload the DNGs if anyone is interested.

I should also point out that the manual makes it clear that a difference exists between 400 and 800 ISO :
The optimum ISO setting for the Blackmagic Cinema Camera is 800ASA.

In bright conditions 400ASA would be best to record richer colors.

If there is no difference in output, why would 400ISO produce richer colours/colors ?

Finally! The Zebra on the camera's display changes depending on what ISO is selected... it has been stated previously that Zebra represents the absolute sensor limit... which implies that analog gain is being applied if ISO affects it.
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m.snell-callanen

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Re: ISO when shooting RAW

PostSun Jun 02, 2013 3:43 pm

I think the manual is saying 400 could be better in bright daylight if you're shooting ProRes or DNX.

I've done similar tests of shooting RAW with all 4 ISO settings and then changing them back to 800 in post. They all look identical to me.
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Juan Salvo

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Re: ISO when shooting RAW

PostMon Jun 03, 2013 1:53 am

Frank Glencairn wrote:Come on guys, in raw, ISO is just metadata - everybody knows that.

Not always. Depends on the camera.
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Dustin Uy

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Re: ISO when shooting RAW

PostMon Jun 03, 2013 9:27 pm

always shoot in 800 ISO.
specially in prores
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Aaron Scheiner

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Re: ISO when shooting RAW

PostMon Jun 03, 2013 9:36 pm

According to one of John Brawley's posts on another thread* the ISO settings in the camera's menu do make a difference. The camera's raw data is 16bit but the DNG output is 12bit. The 16bit output is mapped to the 12bit output and the ISO setting in the menu changes how that mapping is applied.

As an example, 200 ISO will map in such a way as to give more depth to highlights, 400 and 800 will be neutral and 1600 will map to give more depth to shadows(at the expense of losing some highlights).

You can see this shift by watching the zebras as you change ISO in the menu; the zebras will shift depending on the ISO setting.

That said, the difference is barely visible... to know for sure what effect ISO has you'd need to look at the raw data.

*John Brawley's post :
Some people have seen slight differences between 1600 and 800 (but not 400 and 200) in terms of the way the DR works.

When I've pressed BMD about it, the engineers have told me there is a TINY difference in the way they map the 16 bit linear of the camera into the 12 BIT LOG of DNG @ 1600 ISO. So while there is the same DR, they allocate more bits to the bottom end (shadows). The idea being that any noise reduction later might be cleaner.
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Chad Smith

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Re: ISO when shooting RAW

PostTue Oct 22, 2013 10:29 pm

I recently got a number of shots from a client that has the BMCC. I believe that all the shots were taken using 1600 ISO. This camera has the Canon mount. Looking at the DNG files coming out of Resolve all the shots look very noisy and have little detail. When I try and sharpen in Resolve the image falls apart with only 2 clicks of sharpening. (52) I am bringing the clips into Resolve as BMD Film and then applying the Black Magic REC 709 LUT. Is there a better workflow? It seems like something is amiss. I am trying to figure out if it is a camera setting or something that is happening in Resolve. I did however load up one shot into AE with minimal processing and still saw the noise. This is on a Ext Day shot with plenty of light.

I thought I would post this here as I feel it is an ISO issue.

Thanks
Chad Smith
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adamroberts

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Re: ISO when shooting RAW

PostTue Oct 22, 2013 10:43 pm

When shooting RAW the footage is recorded at 800ISO. The camera setting of 1600ISO is simple meta data.

If you click on the Camera RAW panel in Resolve you can adjust how the RAW files are processed.

Processing them as BMC Film is usually best. You can then apply a LUT or grade from the LOG image that is produced.

Check out Color Grading Central. They have a nice free 2 part tutorial on grading BMCC RAW footage.
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Chad Smith

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Re: ISO when shooting RAW

PostWed Oct 23, 2013 3:00 pm

Hi Adam - Yes that is my workflow. However the images that are coming out of Resolve are really not good. Working with RED footage gets a much better result. (have done color work on many features shot on RED)
It must be something I or the shooter is doing. Noisy, not seeing the 12 stops of DR at all, soft, breaks up and looks nasty when sharpening is applied. Have tried pushing DNGs through AE and still have the noise issue on an ext day shot.

When I load footage that Denver put up on his site and do the same workflow it looks great.

Would love to get this sorted out.
Chad Smith
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Tom

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Re: ISO when shooting RAW

PostWed Oct 23, 2013 3:11 pm

Some resources which might help,

A video showing the final visual difference when shooting RAW at various ISO's





A guide to exposing to the right in raw on the BMCC:




It seems to me that the main area of confusion on this thread is that how to best capture raw images is camera specific. Crucially it depends on the Native ISO of the camera in question and whether or not the camera applies analogue gain to achieve different iso values. As such, one best practice for one camera may not be the best for another.

The native ISO of the BMCC is 800. At this setting you will have the largest amount of dynamic range.

When you change the iso value on the bmcc, the clipping point does not change, but the noise floor is pushed down. So lowering the ISO will make the image look cleaner, but you will still be clipping at the same point. So lowering the ISO on this camera in order to help to control the level of light being recorded is not a good idea.

Iso 1600 is a slight exception in that although it is still meta data, the way the range is mapped is different, allocating more bits in the shadows.

As seen in the first video I posted, there is practically no visual difference in the iso values if you digitally balance the exposure in post - proving that it is just meta data. For example, shooting at iso 200 will look the same as shooting at iso 800 and lowering it 2 stops in post - or vice versa.

This is not the same for a DSLR, RED, Arri etc - it is probably the same for the pocket cam.
Tom Majerski
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adamroberts

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Re: ISO when shooting RAW

PostWed Oct 23, 2013 3:19 pm

Chad_S wrote:It must be something I or the shooter is doing. Noisy, not seeing the 12 stops of DR at all, soft, breaks up and looks nasty when sharpening is applied. Have tried pushing DNGs through AE and still have the noise issue on an ext day shot.

When I load footage that Denver put up on his site and do the same workflow it looks great.

Would love to get this sorted out.


Sounds like the footage was badly exposed. Can you share a single DNG file?
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Matt Coppolaro

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Re: ISO when shooting RAW

PostThu Sep 08, 2016 7:07 am

I'm not sure what the science is, but I can tell you that in my experience ISO does have a major impact on RAW. I do a lot of low light shooting with my BMPC 4K, and at ISO 800 the grain resembles thick artifacts and is practically unusable. At ISO 400 I always get tight knit film-style grain. I just lift the brightness in post. I have done many comparisons, and basically ISO 400 is now my default.. I never use 800.
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Eddie Barton

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Re: ISO when shooting RAW

PostThu Sep 08, 2016 11:53 pm

Not all raw cameras use ISO as just metadata. However, in the case of the BM cameras, RED, ARRI, Sony, DB, ISO is a metadata tag. The big difference is in how you expose for each ISO. Instead of losing highlight detail when shifting to a higher ISO, you get more highlight range when properly exposed. Just think of it as "calibrated ETTR/ETTL." Shooting ISO 800 on the BMCC is the same as setting the camera to 200 and underexposing 2 EV, then boosting the two stops in post. And the opposite is true as well. ISO 200 is identical to setting to 800, overexposing 2 EV, and dropping two stops in post. This is because the analog gain never changes in the BM cams. This allows the dynamic range shift like you would see with other popular cinema cameras.

I actually posted graphs of the effect that happens and showed the math behind it in another post. I would say the graphs are very helpful for knowing what to expect when you're exposing your camera.

viewtopic.php?f=2&t=51260#p297150

And here's the post for the math (nerd warning, fairly in depth): viewtopic.php?f=2&t=51260&start=50#p297359
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Thuyen Nguyen

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Re: ISO when shooting RAW

PostMon Sep 12, 2016 1:10 am

Frank Glencairn wrote:Come on guys, in raw, ISO is just metadata - everybody knows that.

Only if you set it to 1600, the curve gets mapped a bit different, to prevent noise in the blacks.
But it still is metadata.

Only exposure matters in the amount of noise or clipped highlights when shooting raw.

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