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Taming Blown Highlights


erniethemilk
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4 minutes ago, SrMi said:

Without clipping on the sensor, you could avoid clipping in the DNG by using an ISO low enough.

I'd like you to demonstrate that please. I don't believe any camera maker (except in cheap P&S) would nobble their own product by clipping the raw file above and beyond what is clipped in the sensor.

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28 minutes ago, SrMi said:

There is clipping on the sensor, and there is clipping in the DNG file

I'm not really understanding this part. There can no clipping on the sensor but the RAW app's handling of the RAW data gives the impression of clipping, specifically LR/ACR's 'hidden' native tone curve, whatever wacky bullshit adobe are doing with LUTs this process generation, whatever luminosity deltas adobe put into their DCP HSD tables for any particular camera, how ever the RAW app choses to work with the DNG maker notes - stuff like that. But that's more of a RAW app thing.

I think I'm miss-understanding you and you mean something different?

20 minutes ago, SrMi said:

When you see clipping in the DNG at higher ISOs, it does not mean that the sensels were saturated, but maybe the ISO "amplification" clipped the data.

 

I'm not really understanding this part either, AFAIK the DNG is created after the exposure parameters have been set and executed.. sure there's some interesting tags in DNG files, like "baseline exposure = -0.5" on the M9 which literally means that every M9 DNG you ever opened in an Adobe product has been darkened before you touched a slider (and also a tag in the M9 that amounts too anti-aliasing filter = YES

Like my amplifier analogy some posts back... you can amplify the music player until the limit of the speakers is reached and it sounds bad, but you didn't break the record - you just need to turn the volume down a bit.

Likewise if you don't clip at capture you didn't break anything by over/under amplification in post

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Ok! So I just went to the bathroom!!

 

The first shot is 100% camera recommended, F2.4 1/60 and ISO400.

Shot 2 is F2.4 1/60 and ISO200

Shot 3 is F2.4 1/60 and ISO800

 

shot 1 and shot 2, with shot 2 receiving a 1 stop global brightness boost. (+1 ev)

 

 

shot 1 and shot 3, with shot 3 receiving a 1 stop global darkening. (-1ev)

 

Obviously this is quick and dirty (erm not that my bathroom isn't a clean place) but as we can see, the exposure was ok(ish - but under IMO) at 400 ISO, but under/over exposing it with ISO didn't make any big problems* to darken or brighten the image to match the exposure in the other two

 

I'm not sure why the reflected light on the sink isn't the same in each shot, I moved a bit between shots maybe!

But amusingly that reflection looks most obviously blown in the unedited iso200 shot!

 

*These days the problem is becoming that you could theoretically add 10 stops of push to a base ISO image from a modern camera, but the exposure slider only goes up to 5!

-------------

None of this is helping Dave (op) not clip stuff at ISO 200 !!!!

 

 

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34 minutes ago, adan said:

I'd like you to demonstrate that please. I don't believe any camera maker (except in cheap P&S) would nobble their own product by clipping the raw file above and beyond what is clipped in the sensor.

Make two shots with the same exposure (same aperture and shutter speed), one at base ISO, so there is no clipping, and a second at ISO 12800. The ISO 12800 shot would likely cause a lot of clipping. Since the amount of light hitting the sensor is the same in both images, we know that the sensor's pixels have not been clipped in both shots. However, the DNG in ISO 12800 shot contains clipped data.

I include an illustration from here:

The red signal is determined by the exposure (shutter speed and aperture). Even though the red signal may not be clipped, the amplification can cause the blue signal to be clipped. 

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27 minutes ago, Adam Bonn said:

I'm not really understanding this part. There can no clipping on the sensor but the RAW app's handling of the RAW data gives the impression of clipping, specifically LR/ACR's 'hidden' native tone curve, whatever wacky bullshit adobe are doing with LUTs this process generation, whatever luminosity deltas adobe put into their DCP HSD tables for any particular camera, how ever the RAW app choses to work with the DNG maker notes - stuff like that. But that's more of a RAW app thing.

I think I'm miss-understanding you and you mean something different?

 

I'm not really understanding this part either, AFAIK the DNG is created after the exposure parameters have been set and executed.. sure there's some interesting tags in DNG files, like "baseline exposure = -0.5" on the M9 which literally means that every M9 DNG you ever opened in an Adobe product has been darkened before you touched a slider (and also a tag in the M9 that amounts too anti-aliasing filter = YES

Like my amplifier analogy some posts back... you can amplify the music player until the limit of the speakers is reached and it sounds bad, but you didn't break the record - you just need to turn the volume down a bit.

Likewise if you don't clip at capture you didn't break anything by over/under amplification in post

The graph I included in response to Adan's question may clarify my point.

The amount of light hitting the sensor is determined by the aperture and the shutter speed (not ISO). The signal read from the sensor is proportional to the luminance from the scene. Assume that the selected exposure does not clip/saturate any of the sensor's pixels. The unclipped signal from the sensor is amplified and stored in the DNG. Too much amplification (too high ISO) will clip the data stored in the DNG.

In the amplifier analogy, you may turn your amplifier too high, which could lead to the distortions in the loudspeakers even though the source does not have distortions.

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1 hour ago, adan said:

I'd like you to demonstrate that please. I don't believe any camera maker (except in cheap P&S) would nobble their own product by clipping the raw file above and beyond what is clipped in the sensor.

Here are two images shot with the same exposure, one with ISO 64 and the other with ISO 3200. Both shots have no clipping in the sensor. However, the ISO 3200 DNG contains a lot of clipping.

 

 

 

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4 minutes ago, SrMi said:

Here are two images shot with the same exposure, one with ISO 64 and the other with ISO 3200. Both shots have no clipping in the sensor. However, the ISO 3200 DNG contains a lot of clipping.

if you made that test with ISO 64 and whatever A/SS then repeated it at ISO 3200 and the same A/SS, would you expect to be able recover all the data to make the 3200 look like the 64 one?

(I think yes... )

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Posted (edited)
13 minutes ago, Adam Bonn said:

(I think yes... )

Ok I just tried with with my M10 and no I'm wrong... I can't recover F4 1/500 3200 to the same image as F4 1/500 @ ISO200 (not even close to be honest)

edit

however RAW digger tells me that I've clipped a lot of data in the 3200 shot, which I take to mean as clipped sensor data

Edited by Adam Bonn
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Posted (edited)
24 minutes ago, Adam Bonn said:

if you made that test with ISO 64 and whatever A/SS then repeated it at ISO 3200 and the same A/SS, would you expect to be able recover all the data to make the 3200 look like the 64 one?

(I think yes... )

No, the data has been lost at ISO 3200. I am talking about "taming the highlights" during the exposure, not after the exposure.

Edited by SrMi
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7 minutes ago, Adam Bonn said:

Ok I just tried with with my M10 and no I'm wrong... I can't recover F4 1/500 3200 to the same image as F4 1/500 @ ISO200 (not even close to be honest)

edit

however RAW digger tells me that I've clipped a lot of data in the 3200 shot, which I take to mean as clipped sensor data

If shooting above base ISO, clipped data in the DNG does not mean that that the data was clipped in the sensor.

 

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Posted (edited)
13 minutes ago, SrMi said:

If shooting above base ISO, clipped data in the DNG does not mean that that the data was clipped in the sensor.

 

you mean that the digital post ADC push (to native ISO) is what is clipping the data?

but the data is lost because the sensor can only create a RAW from the given exposure parameters?

edit:

Sorry Srdjan, I just saw your pictorial explanation in #44, I must have missed it by clicking on the SrMi has quoted you notification... I think you answered this question already and it's yes!

Edited by Adam Bonn
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23 minutes ago, Adam Bonn said:

you mean that the digital post ADC push (to native ISO) is what is clipping the data?

but the data is lost because the sensor can only create a RAW from the given exposure parameters?

edit:

Sorry Srdjan, I just saw your pictorial explanation in #44, I must have missed it by clicking on the SrMi has quoted you notification... I think you answered this question already and it's yes!

Yes, a picture is worth a thousand words 😁.

My point is that sometimes you can avoid clipping during image exposure by reducing the amplification in the camera (i.e., use lower ISO).

If the DNG is clipped, you can only pray that highlight recovery in post can reconstruct the missing data. IMO, that works up to 1EV, but it depends on the image.

 

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