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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 - 2 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.

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