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EXPOSURE - HISTOGRAM - GOAL POSTS : Are you doing it wrong?

J

J Taylor

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Hey Everyone,

I've been renting out my Scarlet package for a few months now and of course everyone is VERY happy with the image and can't believe how easy it is to work with etc. etc.

BUT I've also had people come to me who have been using the histogram and 'goal posts' incorrectly, or I should say 'incorrectly as I see it'

I learned to shoot on RED by reading this forum and asking an old professor who specializes in RED a LOT of questions. My understanding is that to get the best exposure possible and minimize noise, retain color information, and not clip that YOU SHOULD EXPOSE IN RAW MODE. I wanted to start this thread because I've had at least half a dozen people who rented from me not know this.

1) Should you always expose using RAW preview?

2) If you are good on the RAW view goal posts but not the Redcolor3 goal posts and vice versa, how does this affect the final image?

J
 
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It's possible, and even common, for your goal posts + histogram to be spot on perfect in RAW viewing mode and clipped/crushed in REDColor view. Just remember that the goal posts and histogram are reacting to the RGB values of the debayered image, so it's entirely possible for the RGB values to be clipped post-debayer while safely within bounds in your RAW file.
 
Keith Putnam said:
It's possible, and even common, for your goal posts + histogram to be spot on perfect in RAW viewing mode and clipped/crushed in REDColor view. Just remember that the goal posts and histogram are reacting to the RGB values of the debayered image, so it's entirely possible for the RGB values to be clipped post-debayer while safely within bounds in your RAW file.
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So, what you are saying is that it would be nice to be able to apply a REDCINE-X 'look' that is 'close' to the final desired output not just to the monitor output, but to the histogram - as when the look is applied in post, it may push one or more channels into clipping?

Is it possible to apply a 'look' to affect what the histogram sees?
 
Yes if you have a look applied to your footage, then the histogram will show what the exposure is for that look as the histogram is just for the monitor output and doesn't show what is being recorded raw. So having a look on your camera will not change whether or not you are going to clip your sensor, but it will help you to get a better idea of what your final image will look like with the final color.
 
Louis Maddalena said:
Yes if you have a look applied to your footage, then the histogram will show what the exposure is for that look as the histogram is just for the monitor output and doesn't show what is being recorded raw. So having a look on your camera will not change whether or not you are going to clip your sensor, but it will help you to get a better idea of what your final image will look like with the final color.
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I think you are saying this:

1. The 'look' WILL affect the histogram.

2. You can still be clipping in RAW even if the 'look' histogram is OK.

3. You must look at the histogram using the 'look' AND using RAW to be sure you are not clipping a channel.
 
I just ETTR using REDColor, switch to RAW every now and then to make sure no clipping on the right. I try to expose and shoot in native ISO and native K whenever possible. Rarely apply a "look" in camera, I try to keep it flat, knowing what can/cannot be done post.

Its less noisy and richer to bring the image down than to bring the image up, in post...
 
Histogram is metadata and I only use it as an "exposing to the right" indicator (brighter). Goalposts and stop lights are RAW sensor clipping/crushing, so you should avoid having either (especially stop-lights/highlight goal-post).

With that in mind, unless the lighting is completely controlled, ISO800 is where it's at since it'll force you to expose for more highlight retention (and you can always dig into the shadows and apply noise reduction if you need to).
 
Les C. said:
I think you are saying this:

1. The 'look' WILL affect the histogram.

2. You can still be clipping in RAW even if the 'look' histogram is OK.

3. You must look at the histogram using the 'look' AND using RAW to be sure you are not clipping a channel.
Click to expand...

Close. The look wil effect the histogram, however, if you are not clipping the histogram you're not going to clip raw. You can however, be clipping the histogram and not necessarily be clipping the raw. You don't however, need to use the raw check to see if you are clipping the raw, that is what the stop lights and goal posts are for. If a goal post has red in it you are clipping the whites or not getting enough blacks, but a quick way to look at it is if the stop lights to the right of the highlights are lit up. That will indicate if a channel is clipping.
 
It seems very unclear and everyone has a different take on it.

If you are going to be coloring off of redcolor3, then should you just expose based on redcolor3 histogram and posts, or should you still be checking your RAW to make sure it's not clipping.

If you SHOULD check RAW, then what if you have a situation where one or the other clips, is it better to be safe in RAW or safe in redcolor3?
 
J Taylor said:
It seems very unclear and everyone has a different take on it.

If you are going to be coloring off of redcolor3, then should you just expose based on redcolor3 histogram and posts, or should you still be checking your RAW to make sure it's not clipping.

If you SHOULD check RAW, then what if you have a situation where one or the other clips, is it better to be safe in RAW or safe in redcolor3?
Click to expand...


J Taylor said:
2) If you are good on the RAW view goal posts but not the Redcolor3 goal posts and vice versa, how does this affect the final image?
Click to expand...

I'm no expert, but it seems you have the wrong idea about what info the goal posts are giving you.

As far as I know, the goal posts only show you what the sensor is doing and are not influenced by metadata at all.

The REDcolors and REDgammas are metadata. The histogram is affected by them but the goal posts are not.

There is no such thing as a REDcolor3 goal post or a REDgamma2 goal post.

Try this:

1) Lock down your camera on a tripod (or, change settings on a stationary camera with a REDmote) and point it at a static scene with no light fluctuations where you have deep shadow and/or blown highlights so that the left and/or right goal posts and traffic lights light up.

2) Switch between the different color spaces and gammas on the camera.

3) Switch between RAW view and the "normal", metadata influenced view.

You shouldn't see any change whatsoever in the goal posts or the traffic lights (if they were lit). The goal posts, traffic lights and exposure tool are all indications of what the sensor is doing.

The proximity of the goal posts to the histogram, while logical, gives people the idea that there's a direct, 1-to-1 relationship between the histogram and what the sensor is actually doing, which isn't true for RED cameras.

This runs contrary to how other cameras behave but most other cameras cook their data upon recording and aren't based on RAW image capture and metadata. People have to throw out some of what they "know" about how "video" cameras work and re-educate (REDucate) themselves on a few important concepts.

The RED histogram gives you an idea of what your image will look like AFTER transcode or when recording to an external recorder, when your data is baked in, and therefore useful in that respect. But, it should never be used to try to tell what the sensor is doing because it's dependent upon metadata settings.

According to Jim, RC3/RG3 were designed as a monitoring path option and a good starting point for grading.

If you're not clipping the sensor it doesn't matter what REDcolor, REDgamma or REDlogfilm are doing, as they are metadata and can be changed freely.

If you are clipping your sensor, no combination of REDcolor, REDgamma or REDlogfilm is going to reclaim data the sensor didn't capture in the first place.

From RED's website:
http://www.red.com/learn/red-101/red-camera-exposure-tools
 
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Thanks Brian. That's pretty much how I have been interpreting the histogram and goal post tools. Basically expose to the right and avoid any clipping as indicated by the stop light and all is good.
 
Thanks Brian,

that makes a lot more sense. Thank you for taking the time to explain it clearly. Also bob, I've heard expose to the right constantly on the forum so it's something I've incorporated into my shooting, but I'm curious what the actual reason for it is.
 
There are many article online on this subject:

http://www.google.ca/search?client=...oe=UTF-8&redir_esc=&ei=jcorUKWeF-Wx6wHEg4HwCg

RED also have a couple of articles too:
http://www.red.com/learn/red-101/red-camera-exposure-tools
http://www.red.com/learn/red-101/exposure-with-red-cameras


J Taylor said:
Thanks Brian,

that makes a lot more sense. Thank you for taking the time to explain it clearly. Also bob, I've heard expose to the right constantly on the forum so it's something I've incorporated into my shooting, but I'm curious what the actual reason for it is.
Click to expand...
 
I'm setting exposure by goal posts and traffic lights only, as the histogram feels unreliable (the gap, for example).

If I may expand the discussion into HDR, how are you guys setting exposure for HDR, i.e. are you letting the sensor clip by the number of stops you've set HDR for... or do you do something totally different?
 
Petri Teittinen said:
I'm setting exposure by goal posts and traffic lights only, as the histogram feels unreliable (the gap, for example).

If I may expand the discussion into HDR, how are you guys setting exposure for HDR, i.e. are you letting the sensor clip by the number of stops you've set HDR for... or do you do something totally different?
Click to expand...

I haven't done much HDRx shooting but I'm going to go out on a limb and say the method you describe sounds dubious.

Overexposing the sensor by, say, 3 stops and then setting your HDRx to -3 stops of protection gives you a net result of zero and puts you right back where you would've been had you exposed properly.

HDRx is meant to give you additional latitude.

I think the procedure is:

1) Expose your scene normally

2) See what areas in which you want to keep detail may be overexposing

3) Note the amount by which they're overexposing

4) Set HDRx (down to -6 stops of protection) to that amount to compensate

I've seen at least one person suggest overexposing the A-track by 1 stop but I'm not sure why and if he meant overexpose the sensor by 1 stop or overexpose your scene by 1 stop.
 
Brian Boyer said:
I haven't done much HDRx shooting but I'm going to go out on a limb and say the method you describe sounds dubious.

Overexposing the sensor by, say, 3 stops and then setting your HDRx to -3 stops of protection gives you a net result of zero and puts you right back where you would've been had you exposed properly.

HDRx is meant to give you additional latitude.

I think the procedure is:

1) Expose your scene normally

2) See what areas in which you want to keep detail may be overexposing

3) Note the amount by which they're overexposing

4) Set HDRx (down to -6 stops of protection) to that amount to compensate

I've seen at least one person suggest overexposing the A-track by 1 stop but I'm not sure why and if he meant overexpose the sensor by 1 stop or overexpose your scene by 1 stop.
Click to expand...

Bingo.

Early on, Jim cautioned against overexposing the scene and then compensationg with HDRx insofar as you were then committed to the blended mode. If you expose the scene normally and then recover highlights with HDRx, as Brian says, you have a wide range of possibilities.

BTW - I think, if you read the RED articles on exposure noted in Bob's post above, you'll re-evaluate the idea of ETTR.
 
Keith Putnam said:
It's possible, and even common, for your goal posts + histogram to be spot on perfect in RAW viewing mode and clipped/crushed in REDColor view.
Click to expand...

Hi, thanks everyone for all the great information in this thread... One thing I am not too sure about is how to switch to 'RAW viewing mode'... is that when you select ACESproxy in the gamma settings thereby turning off the applied meta colorspace/gamma? Or am I way off? I am new to this aspect of the RED camera so any clarification is much appreciated, thanks :)
 
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