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  • Hey all, just changed over the backend after 15 years I figured time to give it a bit of an update, its probably gonna be a bit weird for most of you and i am sure there is a few bugs to work out but it should kinda work the same as before... hopefully :)

Understanding ISO with the RED ONE

Great thread.

The thing about this discussion I'm a little confused about is what are your histograms showing? Or are you guys literally using a light meter based on an ISO and setting the camera? 'Cause once you've bumped the aperture to change the histogram you've effectively changed the rating of the scene.

For instance, Indoors, lower dynamic range: If you rate the camera at 320 and then use the histograms to set your exposure your net result is about like metering to 160 and exposing there.

If you've got film lighting you're fine. If you're the natural lower light light indie guy... well, crush the blacks. Build 16 may well smooth the transition into underexposure and effectively help speed the camera up in these situations.
 
joelnet said:
Great thread.

The thing about this discussion I'm a little confused about is what are your histograms showing? Or are you guys literally using a light meter based on an ISO and setting the camera? 'Cause once you've bumped the aperture to change the histogram you've effectively changed the rating of the scene.
Click to expand...

When I'm talking about sensitivity and ASA I refer to the results I find using a light meter. I evaluate the shot afterwards in REDCine using a histogram.

Hans
 
My God, this is complicated! :waaa:

Thanks for this post.

I feel like attending REDUser film school.

When do I pay? :)

(Hopefully - early '09 ;) )
 
Simpler rule?

Simpler rule?

karapetkov said:
My God, this is complicated! :waaa:
Click to expand...

How about just adding one stop of fill or bounce board/relector for every stop that you stop down to save highlights.

If you read at 320 then stop down two stops, you read the shade and add two stops of fill to keep the shade out of the noise, then in post darken the shade and you have everything clean and not clipped...
 
Does changing the ISO in the camera really matter, since changing the ISO in Red Alert or REDCine is basically doing the exact same thing? You could make a conscious desicion to underexpose the image 2 stops outdoors at 320 ISO, and it would effectively be the same as shooting 800 ISO. Then in REDcine change that ISO to anything you like, back up to 800 if you wanted to. Changing the ISO in camera is only playing with how you view the material on the LCD. How you expose the image results in how the image can be graded later. Is that a fair assumption? 320 ISO 2 stops underexposed is the same as 800 ISO exposed normally. True or False?
 
Right or left

Right or left

Since this is Mac's thread I have stuck with the concept of changing the camera's ASA setting then setting exposure using the adulterated representation for reference. I find this a bit counterintuitive as an approach but for some film folks this is the preferred method.

The core issue in my mind is whether you are willing to cope with more noise in the toe in order to get a more "filmlike" shoulder by ETTL or accept the clip edge risk (harshness varies depending on material) of ETTR in order to reduce noise levels.
 
fastlayne, it works if you expose to the right but don't over-expose. The in-camera ISO setting, while metadata, does change how the live histogram responds so if you expose to the right properly then this technique becomes a valid way to retain highlights etc.

Of course you are really underexposing by one stop, hence extra shadow noise, but if your highlights are more crucial then you've made the right compromise for the shot's requirements.

Hans, I've seen around 11 stops on a test chart at a couple of clients we've had, though real world usage does probably bring it closer to 9 if you want usable picture without excessive noise. It depends on what you consider usable I guess as to where you draw the line. Anyway, my point wasn't so much about the exact dynamic range as the technique so read it as 9 if that helps.

DANCAD, good idea re: adding 1 stop of fill for every stop you effectively underexpose. Simple and balances out the "expose to the right and light for the shadows" equation.
 
Thanks for taking the time to present your tests so beautifully.
j.
 
fastlayne said:
Does changing the ISO in the camera really matter, since changing the ISO in Red Alert or REDCine is basically doing the exact same thing? You could make a conscious desicion to underexpose the image 2 stops outdoors at 320 ISO, and it would effectively be the same as shooting 800 ISO. Then in REDcine change that ISO to anything you like, back up to 800 if you wanted to. Changing the ISO in camera is only playing with how you view the material on the LCD. How you expose the image results in how the image can be graded later. Is that a fair assumption? 320 ISO 2 stops underexposed is the same as 800 ISO exposed normally. True or False?
Click to expand...

Blair S. Paulsen said:
Since this is Mac's thread I have stuck with the concept of changing the camera's ASA setting then setting exposure using the adulterated representation for reference. I find this a bit counterintuitive as an approach but for some film folks this is the preferred method.
Click to expand...


Well, it would be easier to forget about all this, shot 320ISO and underexpose 1 or 2 stops. But then the image in the LCD would appear too dark. I think that´s the reason for all this. XD
 
Mac

To what degree are you using the Luminance or RGB histogram in the Red LCD/EVF to gauge exposure?

Just curious,
 
So are you saying shoot 5000K no matter what and then just messing with your color temperature in post?

Hans von Sonntag said:
Hi Macgregor,

IMHO, there is no such thing as ISO (ASA) setting in the camera. All you do is changing a LUT for monitoring. RED's sensor is said to have a sensitivity of 320 ASA at 5000K. As with any filmstock its up to the DP to rate REDs sensitivity.

In most cases I find RED more to 250 ASA at 5000K. However, in high contrast scenes 500 ASA might be applicable. In this case there is a trade off towards more noise. If significant oversampling takes place (downconverting from 4K to 1080p or even PAL/NTSC, for instance) the slightly higher noise can be "swallowed" by the oversampling.

Colour temperature below or above 5000K changes the DR and noise level of RED considerably, not to the better.

All around, I fully agree with you.

Hans
Click to expand...
 
Interesting way of skinning this cat.
By "rating" the camera at 800ASA, all you are doing is underexposing by 1 1/3 stops and when matching the greycard, pulling it up 1 1/3 stops in "digital development". Therefore you have 1 1/3 stops more information in your highlights since all you really did is underexpose the Raw image by 1 1/3 stops.
But you also pulled up your "Noise Zone" 1 1/3 stop along your zone.

Rob Peter to pay Paul. Or ISO setting is metadata and has no effect on the RAW image recorded.

The definition of what your noise zone is and what noise level is acceptable to you in the images you want to create for a specific project is what's going to determine how you rate your camera and how you light it. Nothing new to any cinematographer or still photographer imho.

It also brings you back to the old adage of Digital Imaging: Protect the highlights and LIGHT for the shadows (to make up for all the protecting you've done).

And no a Perpetuum Mobile is physically not possible ;)
 
I think the real solution will be to design the Mysterium X (the new one) to be not linear at the top of the curve (fall off in highlights) as film does it.
Some kind of current bleeding device (shottky diode)
http://en.wikipedia.org/wiki/Schottky_diode

Alternatively one can pick the semiconductor characteristics for CMOS photo sites that are not linear in the similar fashion.

ND filters that attenuate more light when more light is trying to get through them is the other solution that will address this problem. (not linear ND filters)
 
Beansmcgibb said:
So are you saying shoot 5000K no matter what and then just messing with your color temperature in post?
Click to expand...

There's no difference between setting your color temperature in-camera and setting it in post. Both do the same thing: apply digital gain to the necessary channels to make your white reference appear neutral.

The key issue here, though, is that the sensor has a native color temperature of around 5000K. At that temperature, it doesn't have to apply different amounts of gain to different channels. So what you really want to do, in an ideal case, is light and/or filter so that your images will look the way you want them to when "developed" at 5000K at around 320 ASA (the ideal ASA depends on scene contrast, as discussed above). The further away from 5000K you are (again, doesn't matter whether you set it in camera or in RedAlert/RedCine), the more chroma noise you'll see.

(I don't want to give the impression that the camera won't deliver reasonable results when processing images at other color temperatures, mind you. Within a reasonable range, it will. But lighting to achieve the desired look at 5000K delivers the best result.)
 
macgregor said:
Well, it would be easier to forget about all this, shot 320ISO and underexpose 1 or 2 stops. But then the image in the LCD would appear too dark. I think that´s the reason for all this. XD
Click to expand...

exactly, simple like this!

As i understand the camera, i like to set ISO one step higher just to alert ME to not overexpose.
Then in post, just go one step back at normal ISO.

Forgot...every iris step down to preserve highlights will increase noise in the shadows for a given dark gray value (visual value).
 
florianstadler.com said:
By "rating" the camera at 800ASA, all you are doing is underexposing by 1 1/3 stops and when matching the greycard, pulling it up 1 1/3 stops in "digital development". Therefore you have 1 1/3 stops more information in your highlights since all you really did is underexpose the Raw image by 1 1/3 stops.
But you also pulled up your "Noise Zone" 1 1/3 stop along your zone.
Click to expand...
I think this is the best explanation of how this whole thing works. However, I'm a bit confused; when I watch Mac's video, and he changes his exposure appropriately to compensate for the ISO shift, he's not just gaining noise in the shadows; he's losing shadow detail completely. Look at the Pelican case on the right. At ISO 320, you can see deep within it, detail of the inner side textures, and full rendering of the cables inside. At ISO 800, it's completely crushed. So if the tradeoff with this system was simply more noise in the darker areas to retain more highlights - in essence, greater dynamic range in exchange for more "digital grain" (as most of the posts here seem to imply) - that would be a reasonable tradeoff a DP could make if he/she so chose. But I am not seeing this in the video - I am seeing a complete shift of usable exposure zones; you either retain shadow detail and blow out your highlights or keep that higlight detail, but lose the shadows AND gain more noise in the darker areas. Is anyone else seeing this in the clip?
 
Yes, i completely agree Haakon.

Maybe it's because when we underexpose to protect highlights,
1) we have to LIFT the shadow info INCLUDING the noise.
2) although it's a 12 bit info, when we "stretch" the steps too much, then...

interestingly...it seems to work EXACTLY like sound recording.
 
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