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09-04-2018, 01:51 PM   #61
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QuoteOriginally posted by normhead Quote
The thing most important to IQ and DR is the amount of light used to form the image. That is determined by exposure.
That is right and in an Iso invariant camera that is via aperture and shutter speed alone - the exposure triangle no longer exists.

09-04-2018, 02:10 PM   #62
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QuoteOriginally posted by GUB Quote
I am querying about the editing of the image - not the taking of it Norm.
Editing the image you can create as much dynamic range as you want limited only by the display device. If you have two values, 0 and 1, and the display values of your monitor or prints are 1 lumin for the 0 black to 400 lumens for the 1, you have a contrast value of 255:1 you can map 8 bits of colour depth to 1 -255 and have 8 EV DR, or you can map them to 124 and 125 and have practically no discernible dynamic range. Output DR is determined by the output device, not the input information.

If your input device is 15 EV, and you have an old digital device only capable of say 7 EV, and your export device is only capable of 5 EV, ( newspaper images where not even that much) it's very likely your images will look similar. PP allows you to both stretch and shrink DR to your approval. The limitation being, the input from your camera will likely have vastly more DR than your output device. The maximum output from film on paper was about 120:1. 124:1 would be 7 EV. You can do a lot higher on a computer monitor or TV, but, you won't get the 13 EV of a K-3 or 15 EV of a K-1. You're going to be shrinking your K-1 or K-3 images, not stretching them. You have to be shooting at an impossibly high ISO before you're going to need to increase your DR.

This image, shot at 20,000 ISO on a K-3 is seriously lacking in DR. Unfortunately increasing the DR to match the output of your monitor would increase noise to for me unbearable levels. You have to find a balance, increased dynamic range vs the overall appearance of the image. When you try and stretch your dynamic range because of lack of DR in your original you are going to run into this kind of issue. Like resolution, most images look better if the camera has more DR than the output device , kind of like oversampling in resolution.



But would anyone believe a black bear tore my garbage bin off the tree it was bolted to, rolled it down my driveway until it broke open, then spread gargbage all over half the county if I hadn't taken this image? There would be doubters. Crap images have their value.

Last edited by normhead; 09-04-2018 at 02:26 PM.
09-04-2018, 02:32 PM   #63
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QuoteOriginally posted by normhead Quote
Editing the image you can create as much dynamic range as you want limited only by the display device. If you have two values, 0 and 1, and the display values of your monitor or prints are 1 lumin for the 0 black to 400 lumens for the 1, you have a contrast value of 255:1 you can map 8 bits of colour depth to 1 -255 and have 8 EV DR, or you can map them to 124 and 125 and have practically no discernible dynamic range. Output DR is determined by the output device, not the input information.

If your input device is 15 EV, and you have an old digital device only capable of say 7 EV, and your export device is only capable of 5 EV, ( newspaper images where not even that much) it's very likely your images will look similar. PP allows you to both stretch and shrink DR to your approval. The limitation being, the input from your camera will likely have vastly more DR than your output device. The maximum output from film on paper was about 120:1. 124:1 would be 7 EV. You can do a lot higher on a computer monitor or TV, but, you won't get the 13 EV of a K-3 or 15 EV of a K-1. You're going to be shrinking your K-1 or K-3 images, not stretching them. You have to be shooting at an impossibly high ISO before you're going to need to increase your DR.

This image, shot at 20,000 ISO on a K-3 is seriously lacking in DR. Unfortunately increasing the DR to match the output of your monitor would increase noise to for me unbearable levels. You have to find a balance, increased dynamic range vs the overall appearance of the image. When you try and stretch your dynamic range because of lack of DR in your original you are going to run into this kind of issue. Like resolution, most images look better if the camera has more DR than the output device , kind of like oversampling in resolution.



But would anyone believe a black bear tore my garbage bin off the tree it was bolted to, rolled it down my driveway until it broke open, then spread gargbage all over half the county if I hadn't taken this image? There would be doubters. Crap images have their value.
I always have struggled with understanding dynamic range.
QuoteOriginally posted by normhead Quote
Editing the image your create as much dynamic range as you want limited only by the display device.
So in editing can I recover the lost dynamic range of an image taken with a higher Iso ?
09-04-2018, 04:26 PM   #64
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QuoteOriginally posted by GUB Quote
Just to clarify for me - In the case of the horse on the beach - by just lightening the shadows and keeping the highlights back and the anchors on the histogram in the same place - does the edited image still have the overall dynamic range of the original Iso 100 image?. (obviously with tonal curves in different areas).
The horse on the beach image illustrates ETTR more so than the merits of ISO invariance. If spot-metering the brightest part of the sky in TAv mode had given ISO 1600 as the "correct" exposure, exposing at ISO 100 would not have helped. But spot metering the dark horse would have resulted in a blown sky, center-weighted might have blown the sky, and who knows whether magical matrix metering might have done the right thing.

That said, exposing at base ISO is more likely to protect highlights than letting ISO float with TAv or other auto-ISO modes (unless the metered reading gives base ISO as the correct exposure).

Exposing at base ISO instead of metered ISO may help preserve highlights in some cases but not all. It's up the photographer to evaluate the scene and decide the appropriate amount of headroom for highlights. Exposing at base ISO does make chimping harder (with a risk of botching the image from not being able to easily review it) and there's always the risk that the amount of pushing might be too high and the photographer should have compromised on shutter speed or aperture to reduce the metered ISO or required post-process push.

09-04-2018, 06:06 PM   #65
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QuoteOriginally posted by GUB Quote
I always have struggled with understanding dynamic range.

So in editing can I recover the lost dynamic range of an image taken with a higher Iso ?
The DR is a quality of the sensor and the amount of light striking it. If the sensor can't pick up the shadows at the shutter speed and aperture you've selected, changing ISO isn't going to help you. You only create more DR by increasing the amount of light available to the sensor. But as a rule, the higher the ISO, the less DR you have to work with. But, you may not get more with base ISO and leaving the bottom end empty, or the top end over exposed.

So you can create dynamic range in post, but you can't recover data you didn't capture with your exposure.

QuoteQuote:
Exposing at base ISO instead of metered ISO may help preserve highlights in some cases but not all. It's up the photographer to evaluate the scene and decide the appropriate amount of headroom for highlights.
Exactly, it's not a hard science, it's judgement calls. Only experience helps understand it. I could try and explain it but I'd just end up tripping all over my own words.

Last edited by normhead; 09-05-2018 at 01:03 PM.
09-04-2018, 07:07 PM   #66
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QuoteOriginally posted by GUB Quote
That is right and in an Iso invariant camera that is via aperture and shutter speed alone - the exposure triangle no longer exists.
Actually, the exposure triangle still exists but the ISO axis could also be labelled the "post processing push" axis.

For example, a tiny sub-triangle of the full exposure triangle for EV=16 which might have these three possible settings that all yield the same image brightness levels:

[1/1000, f/8, ISO 100], [1/1000, f/11, ISO 200]
[1/2000, f/8, ISO 200]

Using ISO invariance with base ISO of 100 and pushing in post could re-define this triangle as:

[1/1000, f/8, ISO 100, Push 0], [1/1000, f/11, ISO 100, Push 1]
[1/2000, f/8, ISO 100, Push 1]

There's still a triangle because there are still the trade-offs of higher and lower shutter speeds with wider and narrower apertures and higher or lower ISO or push-in-post processing.
09-04-2018, 07:16 PM   #67
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QuoteOriginally posted by photoptimist Quote
Actually, the exposure triangle still exists but the ISO axis could also be labelled the "post processing push" axis.

For example, a tiny sub-triangle of the full exposure triangle for EV=16 which might have these three possible settings that all yield the same image brightness levels:

[1/1000, f/8, ISO 100], [1/1000, f/11, ISO 200]
[1/2000, f/8, ISO 200]

Using ISO invariance with base ISO of 100 and pushing in post could re-define this triangle as:

[1/1000, f/8, ISO 100, Push 0], [1/1000, f/11, ISO 100, Push 1]
[1/2000, f/8, ISO 100, Push 1]

There's still a triangle because there are still the trade-offs of higher and lower shutter speeds with wider and narrower apertures and higher or lower ISO or push-in-post processing.
I think it is all in the way you think - I think of it as two variables and an awareness of the perils of unnecessary underexposure ( low signal to noise ratio).
But however you think the outcome is essentially the same. (And the correct setting highly subjective!!).
EDIT How about a compromise? -- it is best visualised as a triangle but there are only two variables.

Last edited by GUB; 09-04-2018 at 07:24 PM.
09-04-2018, 07:24 PM - 3 Likes   #68
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QuoteOriginally posted by GUB Quote
I think it is all in the way you think - I think of it as two variables and an awareness of the perils of unnecessary underexposure ( low signal to noise ratio).
But however you think the outcome is essentially the same. (And the correct setting highly subjective!!).
Yes it is subjective. But there really are three distinct variables at play that affect three different dimensions of image quality:

[1/1000, f/8, ISO 100, Push 0]: more motion blur, less DoF, less noise
[1/1000, f/11, ISO 100, Push 1]: more motion blur, more DoF, more noise
[1/2000, f/8, ISO 100, Push 1]: less motion blur, less DoF, more noise

It comes down to trade-offs in motion blur, DoF, and noise as modulated by shutter speed, aperture, and either ISO gain or post-processing push.

12-13-2019, 08:15 AM   #69
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For what it's worth, I'm not sure the newer pentax cameras are 'ISO invariant' anyway. I took a few shots with the KP (constant aperture and shutter speed) and slowly increased ISO by 1 stop at a time (up to +4). Went into LR and raised exposure in all to match. My photos taken with the correct exposure were always better than photos bumped up in post. This was true whether it was ISO 100 - 800 or 1600 - 12800 I also, in all honestly, have no idea what the sensor accelerators do on the newer cameras (KP, K1 ii, etc.). Maybe you guys know more.
Sorry to revive an old thread!
12-13-2019, 05:22 PM   #70
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QuoteOriginally posted by eric3929 Quote
I'm not sure the newer pentax cameras are 'ISO invariant' anyway.
ISO invariant is a term like equivalence that just mucks up photography forums and doesn't do anybody any good.
QuoteOriginally posted by eric3929 Quote
My photos taken with the correct exposure were always better than photos bumped up in post.
This post explains it better than I can:
QuoteOriginally posted by photoptimist Quote
The horse on the beach image illustrates ETTR more so than the merits of ISO invariance. If spot-metering the brightest part of the sky in TAv mode had given ISO 1600 as the "correct" exposure, exposing at ISO 100 would not have helped. But spot metering the dark horse would have resulted in a blown sky, center-weighted might have blown the sky, and who knows whether magical matrix metering might have done the right thing.That said, exposing at base ISO is more likely to protect highlights than letting ISO float with TAv or other auto-ISO modes (unless the metered reading gives base ISO as the correct exposure).Exposing at base ISO instead of metered ISO may help preserve highlights in some cases but not all. It's up the photographer to evaluate the scene and decide the appropriate amount of headroom for highlights. Exposing at base ISO does make chimping harder (with a risk of botching the image from not being able to easily review it) and there's always the risk that the amount of pushing might be too high and the photographer should have compromised on shutter speed or aperture to reduce the metered ISO or required post-process push.
QuoteOriginally posted by eric3929 Quote
I also, in all honestly, have no idea what the sensor accelerators do on the newer cameras (KP, K1 ii, etc.). Maybe you guys know more.
Unless a Pentax engineer involved with developing those cameras is lurking on this forum, the answer is no. I would summarize the ISO invariant argument as camera users trying to prove they are smarter than the people who design the cameras.
12-13-2019, 06:56 PM   #71
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QuoteOriginally posted by eric3929 Quote
For what it's worth, I'm not sure the newer pentax cameras are 'ISO invariant' anyway. I took a few shots with the KP (constant aperture and shutter speed) and slowly increased ISO by 1 stop at a time (up to +4). Went into LR and raised exposure in all to match. My photos taken with the correct exposure were always better than photos bumped up in post. This was true whether it was ISO 100 - 800 or 1600 - 12800 I also, in all honestly, have no idea what the sensor accelerators do on the newer cameras (KP, K1 ii, etc.). Maybe you guys know more.
Sorry to revive an old thread!
Could you clarify your test. Which was the "correct" exposure? It needs to be the "+4" one. So in manual mode take a "correct" exposure at your higher iso at take progressively underexposed shots by decreasing the iso and correcting these in post. This may be what you did but your wording is confusing. I would hate to think that later generations of cameras are moving away from being iso invariant but I gather it might be to do with the accelerator units in like the K1ii. From memory it is something like iso-invariant above iso 400.
QuoteOriginally posted by RGlasel Quote
ISO invariant is a term like equivalence that just mucks up photography forums and doesn't do anybody any good.
maybe for a jpg shooter.
12-13-2019, 07:03 PM   #72
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QuoteOriginally posted by RGlasel Quote
I would summarize the ISO invariant argument as camera users trying to prove they are smarter than the people who design the cameras.
No one is attempting to be smarter than others. Iso-invariance is a feature of the recent Sony sensors. It is simply good practise to utilise it to gain more control over your highlights if that is what you wish.
12-14-2019, 01:31 PM   #73
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QuoteOriginally posted by GUB Quote
Could you clarify your test.
Thanks for pointing out the confusing language. I looked back and what I wrote made no sense (and doesn't even reflect the test I did). I set up the triad to expose correctly with ISO at 100. I then kept ISO and aperture constant, and increased SS to underexpose by 1 stop, 2 stops, etc. I repeated this at a few different ISOs. What I found was that at any ISO, I had better results by shooting at correct exposure than I did by increasing exposure +1, +2, etc in LR. I hope this makes more sense now. I had heard that because of the ISO invariance, I could get away with underexposing shots at night by keeping ISO low and raising exposure in post. I think this is what my test was simulating - but if I should have set it up differently let me know.

On a side note, the KP and the K1 ii (with the sensor accelerators) show a non-linear relationship between dynamic range and ISO (at least according to the charts on PhotonstoPhotos). The older cameras (K1, K3, etc.) show a linear relationship.
12-14-2019, 09:39 PM   #74
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QuoteOriginally posted by eric3929 Quote
On a side note, the KP and the K1 ii (with the sensor accelerators) show a non-linear relationship between dynamic range and ISO (at least according to the charts on PhotonstoPhotos). The older cameras (K1, K3, etc.) show a linear relationship.
I think that means they are not iso invariant but does the relationship become linear above iso 400?

QuoteOriginally posted by eric3929 Quote
I set up the triad to expose correctly with ISO at 100. I then kept ISO and aperture constant, and increased SS to underexpose by 1 stop, 2 stops, etc
This set up is exactly the wrong way to do it. Think of the aperture and shutter as putting a quantity of light on the sensor and the Iso applying amplification to the resulting signal.
So you under exposed by cutting back that quantity of light and thereby starving the sensor - hence more noise in the signal/noise ratio.
This is supposed to be a test of comparing increased EV in PPing against the noise from Higher Iso
Try replicating your test but make the correct exposure at iso 3200 and decreasing iso to under-expose.
12-15-2019, 05:04 PM   #75
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QuoteOriginally posted by GUB Quote
Think of the aperture and shutter as putting a quantity of light on the sensor and the Iso applying amplification to the resulting signal.
Thanks for your feedback! I understand your suggestion and I've repeated the test. I did two rounds of constant aperture and SS. In the first I correctly exposed with ISO 6400 and then proceeded to drop to 3200, 1600, 800. In the second I correctly exposed at 800 and dropped to 400, 200, and 100. While I can discern a difference between the images, I'll say they are really quite comparable to one another now. These are more in alignment with the results I had been expecting when I did the first test. Thanks for your tips GUB.
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