“Expose to the Right” & relation to ISO Invariance

[Bart_van_der_Wolf]

when dealing with Adobe converters do use gutted .dcp profiles (linear curve, hidden expocorrections compensated, post exposure corrections LUTs removed) + Process 2010 + brightness 50, contrast 25, curve : Medium Contrast, output to the baddest gamut-wise colorspace... something like this... at least in ACR.

Correct. In fact, LR's Process 2012 conversions are useful in practice for conversions of images with (potential) clipping issues. However, for analysis of Raw data it is less suited because there is indeed too much going on (it's not obvious what is real data related and what is constructed) under the hood of LR to draw any meaningful technical conclusions. It can reconstruct detail from (partially) clipped highlights pretty good, but that is extrapolated data. So when the clipping indicator indicates nothing, there may still be clipped data. Useful for rescuing highlights, not so much for analysis, or for learning how to improve one's technique.

To inspect the really Raw data one needs a tool like Rawdigger. It will tell if there is clipping when the Raw (linear gamma, no WB) histogram collects increasing amounts of data in the highest bin of the histogram.

Cheers,
Bart

[jrsforums]

Years ago, Emil Martinec posted the following where he equated ETTR with Maximizing Exposure

What is the appropriate mantra? I would prefer "Maximize Exposure"; maximize subject to three constraints:
(1) maintaining needed DoF, which limits how much you can open up the aperture; (2) freezing motion, which limits the exposure time;
(3) retaining highlight detail, by not clipping wanted highlight areas in any channel.
Note that ISO is not part of exposure; on many cameras (those with CCD sensors, and the newer Sony Exmor sensors), there is little or no advantage to raising the ISO, which compromises point (3), even though leaving the ISO at a low value may leave the histogram "to the left" for your chosen exposure; such cameras can safely be operated at close to their lowest ISO (the precise optimal ISO depends on the details of a given camera design). On many other CMOS sensor'd cameras, such as Canon's offerings, and Nikons with Nikon-designed CMOS sensors (D3/D700/D3s, for example), noise relative to exposure is improved by increasing the ISO; after you have maximized the exposure (ie by satisfying criteria (1) and (2)), you have a tradeoff to make for (3) -- raising the ISO lowers shadow noise (up to a camera-specific point of diminishing returns, usually about ISO 1600), therefore improving S/N, but reduces highlight headroom for your chosen exposure, so one has to decide how high the ISO can go and still keep wanted highlights unclipped.
Anyway, the prescription is to set the exposure (shutter speed and aperture only) according to (1) and (2); back off the exposure if at base ISO and you are compromising (3). If you are compromising (3) with your chosen exposure and you are not at base ISO, then you should have started with a lower ISO. Afterward, depending on the specifics of the camera's noise profile, further optimization results from raising the ISO, up to the limit specified by (3), or the camera's ISO point of diminishing returns, whichever is arrived at first.
So, it's (almost) all about ME.

[digitaldog]

Note that ISO is not part of exposure; on many cameras (those with CCD sensors, and the newer Sony Exmor sensors), there is little or no advantage to raising the ISO,

Yet that doesn't appear to be the case with Canon systems.

[jrsforums]

Yet that doesn't appear to be the case with Canon systems.

I hope you have, by now, finished reading the quote,  where this is discussed.

[digitaldog]

I hope you have, by now, finished reading the quote,  where this is discussed.

The two parts of the quote that contradict each other, yes.

[jrsforums]

The two parts of the quote that contradict each other, yes.

ISO is not part of exposure.  It is, on certain sensors, a part of maximizing exposure considerations of aperture and shutter speed.  Thereby allowing faster shutter or smaller aperture with a less than linear reduction in dynamic range and/or increase in noise.

[AlterEgo]

To inspect the really Raw data one needs a tool like Rawdigger.

absolutely, but if smb still want to use Adobe converters this is the easiest set of parameters, then the said individual might go deeper and try may be altering ColorMatrix'es inside .dcp to make proper use of UniWB (I didn't do that myself though - as I have both RD anf FRV)

[digitaldog]

ISO is not part of exposure.  It is, on certain sensors, a part of maximizing exposure considerations of aperture and shutter speed.

OK, that's clear. It is and it isn't.

[jrsforums]

OK, that's clear. It is and it isn't.

Come on Andrew.  ISO has nothing to do with the amount of light reaching the sensor. 

It is also known that increasing ISO will increase noise and lessen dynamic range. The amount of the change is dependent of the amplification characteristics.  Knowing how your camera reacts is important to the image you want to create....which we often call, improperly, exposure.

[digitaldog]

Come on Andrew.  ISO has nothing to do with the amount of light reaching the sensor.  

I agree IF we accept that exposure is solely the relationship of aperture and shutter speed. I think that's probably true but have an open mind.

It is also known that increasing ISO will increase noise and lessen dynamic range.

Expect when it doesn't. In the example I provided, the increased ISO reduced the noise.

The amount of the change is dependent of the amplification characteristics.  Knowing how your camera reacts is important to the image you want to create....which we often call, improperly, exposure.

No argument, I fully agree. But there's something going on, something 'good' when the Canon is set to a higher ISO with the same 'exposure' the meter recommended. I don't think that is something to be dismissed. The image of the dog with the higher ISO has less visible noise.

[bjanes]

ISO is not part of exposure.  It is, on certain sensors, a part of maximizing exposure considerations of aperture and shutter speed.  Thereby allowing faster shutter or smaller aperture with a less than linear reduction in dynamic range and/or increase in noise.

The usual definition of exposure is given in this Wikipedia article:

"In photography, exposure is the amount of light per unit area (the image plane illuminance times the exposure time) reaching a photographic film or electronic image sensor, as determined by shutter speed, lens aperture and scene luminance. Exposure is measured in lux seconds, and can be computed from exposure value (EV) and scene luminance in a specified region."

Changing the ISO setting on the camera has no effect on the number of lux-seconds falling on the sensor. ACR and other raw converters use the term exposure loosely and this "exposure" adjustment only changes the apparent brightness of the rendered image by applying a scaling factor (if one is lucky and there are no hue twists or other untoward effects). Likewise, some photographers regard increasing the ISO setting on the camera as changing exposure, but this is not scientifically correct.

Bill

[jrsforums]

Here's a screen capture of the entire image also showing the somewhat radical settings used in Develop. Clipping indicators are on in Histogram, no clipping. RGB value over brightest area of dogs head reads 98%.
What's interesting (to me) is that while the 'exposure' was boosted 3 stops via ISO, note that the Exposure slider is set to -1.55 stops which as I pointed out earlier is just about the limit of the ETTR testing on this camera done in the past. I can't explain why there is this disconnect between the +3 ISO and -1.5 Exposure slider among the other sliders as set.

At 98%, the whites have at least one channel clipped and LR has recovered.  Check under RawDigger or PV2010.

+3 EC on what exposure and exposure mode.  More than likely, due to the amount of white in the image, it probably should have been underexposed with no EC.  At +3, it only need -1.55 to set exposure properly.

[digitaldog]

The usual definition of exposure is given in this Wikipedia article:

"In photography, exposure is the amount of light per unit area (the image plane illuminance times the exposure time) reaching a photographic film or electronic image sensor, as determined by shutter speed, lens aperture and scene luminance. Exposure is measured in lux seconds, and can be computed from exposure value (EV) and scene luminance in a specified region."

I'm simply wondering if the usual definition is sufficient. I'm fine accepting it, I'm fine if, as I've seen in the past with the usual smart people here, it needs some updating.
Case in point, I think you may recall the long decision here about color numbers and colors we can see. Not the same. This was nicely hashed out here. Yet go to Wikipedia and they say:

The RGB color model is implemented in different ways, depending on the capabilities of the system used. By far the most common general-used incarnation as of 2006 is the 24-bit implementation, with 8 bits, or 256 discrete levels of color per channel. Any color space based on such a 24-bit RGB model is thus limited to a range of 256×256×256 ≈ 16.7 million colors.

Can we see 16.7 million colors? If we have a color number that represents something we can't see, is it a color?

I think this group can possibly refine, if necessary, ETTR, exposure and ISO. Maybe not. If the consensus is, exposure is solely an attribute that doesn't include ISO, I think it useful to come up with some language that describes what happened and why with the ISO 800 image that has less noise than the ISO 100 image. If we agree to separate ISO, the E in ETTR doesn't apply here. But that doesn’t mean we should ignore it so what do we call it?

[digitaldog]

At 98%, the whites have at least one channel clipped and LR has recovered.  Check under RawDigger or PV2010.

That is entirely possible, but not really pertinent to the effect seen. Suppose I altered the exposure or ISO just a tad? Do you suspect the noise would then match that of the ISO 100 capture or it would appear less noisy? I suspect the later. So I think the fact that one channel might be clipped is minutia when the question I'm asking about is the effect of using a higher ISO with the same exposure and it's effect on the noise and what do we call this, how do we describe it to others who have stated "higher ISO always produces more noise"?

[jrsforums]

Exactly and as you pointed out first, in terms of ISO/ETTR, depends on the camera. Example of a Canon 5DMII:



ISO 100, more noise than ISO 800.

You cannot check ISO noise by changing ISO, then adjusting in post.  You must reduce the exposure one stop for each stop increase in ISO.

At 800 with the 5D3 you would not see much change.  However,  noise vs 100 would increase slightly and dynamic range would decease.  While the Sony Exmore sensors have almost a linear decrease the 5d3 is fairly flat thru 1600 and a deeper angle to 3200, then goes roughly linear.

[digitaldog]

You cannot check ISO noise by changing ISO, then adjusting in post.  You must reduce the exposure one stop for each stop increase in ISO.
At 800 with the 5D3 you would not see much change.  However,  noise vs 100 would increase slightly and dynamic range would decease.  While the Sony Exmore sensors have almost a linear decrease the 5d3 is fairly flat thru 1600 and a deeper angle to 3200, then goes roughly linear.

I don't understand. You have two captures I provided from a 5DMII. There's a very visible difference in the noise no? And it appears DR. One looks better to me. It's the capture set at ISO 800.

[jrsforums]

I don't understand. You have two captures I provided from a 5DMII. There's a very visible difference in the noise no? And it appears DR. One looks better to me. It's the capture set at ISO 800.

You took them at the same exposure (aperture/shutter) and changed ISO, the adjusted in post.....which you cannot do to compare ISO.

[jrsforums]

The attached shows the change (reduction) in dynamic range by ISO for the D800 and 5D3.  Notice how the D800 reduce approximately on a linear basis, while the 5D3 is flat in the early part.

The noise change (increase) follows these curves in the (logical) inverse....that is, the D800 increases on a linear basis, where the 5D3 increase only a little at first, the goes linear around 1600-3200

[digitaldog]

You took them at the same exposure (aperture/shutter) and changed ISO, the adjusted in post.....which you cannot do to compare ISO.

Let's try this again. All I want is:
A. One good sentence or paragraph to describe what happened with the ISO 800 image that resulted in less noise.
B. Agreement on what to call this 'technique' other than ETTR since it's presumably not a part of exposure.
C. Agreement on whether what I see by upping the ISO is beneficial (it appears to me that it is).

[jrsforums]

Let's try this again. All I want is:
A. One good sentence or paragraph to describe what happened with the ISO 800 image that resulted in less noise.
B. Agreement on what to call this 'technique' other than ETTR since it's presumably not a part of exposure.
C. Agreement on whether what I see by upping the ISO is beneficial (it appears to me that it is).

How did you get the 100 ISO and 800 ISO images to look the same?  Underexpose the 100, the increase "exposure" in post?