September 26, 2017, 12:40:45 PM

Author Topic: Histogram question regarding clipping  (Read 4001 times)

sulla

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Re: Histogram question regarding clipping
« Reply #15 on: August 19, 2017, 12:32:05 PM »
Who tell you Lightroom histogram lie?
Lie? In a sense of not-telling-the-whole-truth: yes.
Try the following experiment: From a perfectly exposed RAW, i.e. without over- and under-exposed parts (no clipping on either side), if you import it in LR and push the highlights/whites, then the histogram will clip, although the RAW contains full data and does not clip. Yes, LR histogram lies.
Following real situation: Image exposed such, that some highlight clipping is shown in-camera, but actually not in RAW. Import it to LR, and histogram will still clip. bring down highlights/whites will bring back all the details. Now histogram will not clip any more. So yes: LR histogram lies in some sense.

What the histogram should do: It should show the full scale of the RAW and then overlay to this borders on the high and low side which will show you the constraints of the current image format, JPG, say. This way you would see that there is no clipping in the RAW-data and that by bringing down highlights / pushing shadows you can bring those details back.
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Re: Histogram question regarding clipping
« Reply #15 on: August 19, 2017, 12:32:05 PM »

SecureGSM

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Re: Histogram question regarding clipping
« Reply #16 on: August 19, 2017, 12:39:23 PM »
Sulla, not quite correct. The Canon RAW 14-bit file format contains an extra headroom in highlights area. So clipped highlights still can be recovered in many cases. That has nothing to do with Lightroom at all. Ask Private by Design. He should be able to explain this better.
« Last Edit: August 19, 2017, 12:44:46 PM by SecureGSM »

Joules

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Re: Histogram question regarding clipping
« Reply #17 on: August 19, 2017, 01:42:04 PM »
Sulla, not quite correct. The Canon RAW 14-bit file format contains an extra headroom in highlights area. So clipped highlights still can be recovered in many cases. That has nothing to do with Lightroom at all. Ask Private by Design. He should be able to explain this better.
I think all Sulla is saying is that he'd like to have a histogramm that displays the entire dynamic range of the RAW file, including this extra headroom, to know how much he can recover in post.

I'd like to have that too. When I go trough my RAWs, I sometimeshave to bring down their exposure a little before being able to select which one is exposed the best, because I can't tell in LR based on the initial histogram. (I shoot multiple exposure settings when I can, because i'm not great at it so I like to have some options).

That's also why I'd like to try putting together a little RAW editor that's tweaked for my taste. I'll try to implement an option for saving the images as non-debayered dng files, so that I can still do all I usually do in LR.
« Last Edit: August 19, 2017, 02:38:27 PM by Joules »

Mikehit

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Re: Histogram question regarding clipping
« Reply #18 on: August 20, 2017, 03:15:03 PM »
On all canon cameras I have owned, I find that the raw file has about 1 stop headroom compared to what the in-camera histogram shows. And when viewing the image on the screen I will allow a small amount of blinkies and find that the data there is recoverable.

The luminance histogram can be deceptive especially regards the red channel - I have had luminance histogram look fine but red poppies turn orange because the red channel has blown badly.

snoke

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Re: Histogram question regarding clipping
« Reply #19 on: August 21, 2017, 08:18:25 AM »
The luminance histogram can be deceptive especially regards the red channel - I have had luminance histogram look fine but red poppies turn orange because the red channel has blown badly.

Use RGB histogram, not luminance and you see channel clip.

snoke

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Re: Histogram question regarding clipping
« Reply #20 on: August 21, 2017, 08:36:43 AM »
Who tell you Lightroom histogram lie?
Lie? In a sense of not-telling-the-whole-truth: yes.

No. Who tell you lie about Lightroom histogram?

LR histogram = ACR histogram. Same logic.

Quote
Try the following experiment: From a perfectly exposed RAW, i.e. without over- and under-exposed parts (no clipping on either side), if you import it in LR and push the highlights/whites, then the histogram will clip, although the RAW contains full data and does not clip.

Following real situation: Image exposed such, that some highlight clipping is shown in-camera, but actually not in RAW. Import it to LR, and histogram will still clip. bring down highlights/whites will bring back all the details. Now histogram will not clip any more. So yes: LR histogram lies in some sense.

What the histogram should do: It should show the full scale of the RAW and then overlay to this borders on the high and low side which will show you the constraints of the current image format, JPG, say.

Raw engine is same for LR & ACR. Both lie or not lie. Not one.

But you confused.
« Last Edit: August 21, 2017, 09:24:54 AM by snoke »

zim

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Re: Histogram question regarding clipping
« Reply #21 on: August 21, 2017, 09:17:48 AM »
Can any topic in CR actually end without insults any more..... sigh

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Re: Histogram question regarding clipping
« Reply #21 on: August 21, 2017, 09:17:48 AM »

Joules

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Re: Histogram question regarding clipping
« Reply #22 on: August 21, 2017, 09:58:28 AM »
Raw engine is same for LR & ACR. Both lie or not lie. Not one.
As far as i can tell there is no debate here about whether or not the Lightroom and Adobe Camera RAW Histograms are the same. That is something you read into the conversation, so it seems you are confused. or am I missing something? I think it's common knowledge that both programs share some technical components, including the RAW engine. I see nobody claiming something else.

Sulla's point was that Lightroom's Histogram shows the information from the current state of the edited picture and not the information from the underlying RAW file. Which can be seen as a distortion of information, and therefore be called a "lie" in some sense. Another term that you brought into the conversation, by the way.

So what's your point? I feel like we're discussing a misunderstanding.

snoke

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Re: Histogram question regarding clipping
« Reply #23 on: August 21, 2017, 10:37:38 AM »
Raw engine is same for LR & ACR. Both lie or not lie. Not one.
As far as i can tell there is no debate here about whether or not the Lightroom and Adobe Camera RAW Histograms are the same.

I know what you say. CR forum say histograms different. Adobe say histograms same.

Quote
Sulla's point was that Lightroom's Histogram shows the information from the current state of the edited picture and not the information from the underlying RAW file. Which can be seen as a distortion of information, and therefore be called a "lie" in some sense.

ACR is same. It show histogram after changes too. You never make change to image in ACR?

Joules

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Re: Histogram question regarding clipping
« Reply #24 on: August 21, 2017, 11:04:22 AM »
ACR is same. It show histogram after changes too. You never make change to image in ACR?
Precisely. The histogram for both programs changes as you make edits to your image. The reason for that is that the histogram on display shows the information of the edited picture. It shows the information of the output image, if you will. Just like the camera shows the histogram of the JPEG it would output.

Neither shows all the information from the actual RAW file. That's all that was ever said here. Do you disagree with that? It that case, run the experiment described by Sulla to see the proof. I still think there is a misunderstanding here.
« Last Edit: August 21, 2017, 11:06:46 AM by Joules »

sulla

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Re: Histogram question regarding clipping
« Reply #25 on: August 21, 2017, 06:34:34 PM »
I already wanted to retreat from this discussion, but now that I see it becoming more productive again, I somehow feel that I am obliged to reengage, as my earlier contributions lead to considerable misunderstandings. So, I would like to add this:

I don't consider the "additional headroom of ~1 stop" in the RAW files over the in-camera displayed histogram an "additional bonus" you get from shooting RAW, but I consider the canon / adobe algorithm of calculating and displaying the histogram as hiding from the user ~1stop of dynamic range that is actually present in the sensor data. That algorithm is what I - and apparently Juoules, too - am not really happy with and that leads to the situation that there is no Canon way to know in the field whether an exposure acutally clips or not and that makes exposure-to-the-right quite difficult.

But we learned from earlier contributions that there is a MagicLantern way to tell right away whether sensor data clip.

I take away from this passionate discussion that I really should give MagicLantern a try. So far I unfortunately haven't.
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scyrene

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Re: Histogram question regarding clipping
« Reply #26 on: August 21, 2017, 07:07:01 PM »
Can any topic in CR actually end without insults any more..... sigh

Insults? I must have missed that. A fair bit of talking at cross purposes, which is par for the course.
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privatebydesign

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Re: Histogram question regarding clipping
« Reply #27 on: August 21, 2017, 07:10:32 PM »
A large part of the dissonance in this thread is based on an opinion that is not entirely correct, which is based on a misunderstanding of what Lightroom is actually showing you. In the Library module it is, effectively, showing you a jpeg in a small color space and the histogram reflects that, in the Develop module it is showing you something entirely different.

Lightroom does a lot of heavy lifting under the bonnet to make things seem effortless in the interface, trouble with that is it leads to many false assumptions. If you want to see your histogram from the RAW data look at the Develop module, the histogram there is the full depth information mapped into the Melissa RGB color space, which is the ProPhoto color range with an sRGB gamma curve applied (it is a custom color space used in the Develop and Print modules).

Here is an illustration. First screenshot from the Library Module with a clearly clipped (but missing spike) histogram, second screenshot same image no adjustments but from the Develop Module with highlights that are clipped but present.

So why does it do this?

The Library module is working in a different color space with a smaller gamut and the histogram is a reflection of the image as you see it, WYSIWY have. The Develop module is working in a much bigger color space and again is showing you a real time analysis of what is on the screen. By the way, the Develop module only does this for RAW files, it is quite amazing how much thought Adobe put into color management within the software so we don't need to give it a thought.
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Re: Histogram question regarding clipping
« Reply #27 on: August 21, 2017, 07:10:32 PM »

sulla

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Re: Histogram question regarding clipping
« Reply #28 on: August 21, 2017, 07:24:49 PM »
I knew that the develop module uses different data than the library module, as, e.g., it builds its own preview, during which at first it displays the library-module preview. I did not know, however, that it uses a different colour space and that it displayed a histogram with a greater dynamic range than the library module. I never noticed that colours and tones shift as soon as the develop module switches from the library-module-preview to its own preview. Next time I'll try to observe that carefully.
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neuroanatomist

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Re: Histogram question regarding clipping
« Reply #29 on: August 21, 2017, 07:54:50 PM »
@sulla - for in-camera exposure, you might Google 'Canon UniWB'.
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Re: Histogram question regarding clipping
« Reply #29 on: August 21, 2017, 07:54:50 PM »