ETTR & post processing

[ario]

Can I expose to the right by increasing the ISO, or is it always better to ETTR by pushing the shutter speed or aperture?

Increasing the ISO normally does not help, at least in the isoless cameras. In the non-isoless cameras it has to be seen case by case.

[mouse]

Can I expose to the right by increasing the ISO, or is it always better to ETTR by pushing the shutter speed or aperture?

It depends on your camera (sensor).  With some cameras pushing the exposure (to the right) by increasing ISO will result in more noise compared to using shutter speed or aperture.  With other cameras (so called "iso invariant sensors) the results will be pretty much identical.  There's a raft of information on this subject in this forum.

[EricV]

Can I expose to the right by increasing the ISO, or is it always better to ETTR by pushing the shutter speed or aperture?

The point of ETTR is to provide more light to the sensor.  Increasing ISO only provides higher electronic amplification of the existing light.  This may help in some circumstances on some cameras, but is always better to provide more light.  Raising ISO and then following the camera exposure meter recommendation (rather than over-exposing) will actually result in less light on the sensor, the exact opposite of what you want.

[digitaldog]

The point of ETTR is to provide more light to the sensor.  Increasing ISO only provides higher electronic amplification of the existing light.  This may help in some circumstances on some cameras, but is always better to provide more light.  Raising ISO and then following the camera exposure meter recommendation (rather than over-exposing) will actually result in less light on the sensor, the exact opposite of what you want.

Right on. If you can implement ETTR (or I prefer, optimal exposure for raw), by providing more light, do so.
Where raising ISO in cameras that support this can be useful would a situation under low light levels where you're shooting wide open anyway and can't slow down the shutter further.

[AlterEgo]

Can I expose to the right by increasing the ISO

ISO (or gain) is not a part of exposure... it is a part of your decision about the exposure (aperture and exposure time) that you make before the actual exposure happens and the effects of your choice (about gain) are applied post actual exposure, the rest if said above

[texshooter]

The more I Google the subject of ETTR, the more Excedrin I take. So what I need are rules of thumb. So here's my best shot:

Rule 1: it is always better to ETTR using shutter or aperture  instead of using ISO.
Rule 2: It is always better to ETTR low dynamic scenes than high ones.
Rule 3: It is always better to expose for middle gray (ETTM) at a lower ISO than to ETTR at a higher ISO.


How am I doing so far?

[mouse]

The more I Google the subject of ETTR, the more Excedrin I take. So what I need are rules of thumb. So here's my best shot:

Rule 1: it is always better to ETTR using shutter or aperture  instead of using ISO.
Rule 2: It is always better to ETTR low dynamic scenes than high ones.
Rule 3: It is always better to expose for middle gray (ETTM) at a lower ISO than to ETTR at a higher ISO.


How am I doing so far?

I think you could condense it down to one rule:

It is always better to ETTR (I prefer dd's phrase "optimal exposure for raw") using only shutter or aperture whenever you can.  Where shooting conditions do not allow adjustment of shutter or aperture it is better to ETTR using ISO (most modern sensors) than to ETTM and boost shadows in post.

[Tony Jay]

Surely using the term ETTR and an ISO other than base ISO is an photographic exposure oxymoron?

Tony Jay

[Jack Hogan]

The more I Google the subject of ETTR, the more Excedrin I take. So what I need are rules of thumb. So here's my best shot:
How am I doing so far?

My take is that you first max out Exposure with shutter speed and f-number at base ISO based on artistic constraints. Then, depending on your camera, if the brightest desirable highlights are not all the way to the right of the raw histogram you may increase ISO so that they are (up to a point).  More details at http://www.strollswithmydog.com/exposure-and-iso/.

Jack

[bjanes]

Surely using the term ETTR and an ISO other than base ISO is an photographic exposure oxymoron?

Tony Jay

I agree 100% here, but when practicing ETTR we have a conundrum: we are using the histogram to  evaluate exposure, but the histogram by itself does not indicate exposure. Exposure is the amount of light falling on the sensor and (for the technically oriented) is measured in lux seconds. For a given illumination and subject reflectance, exposure is determined by the shutter speed and f/stop. Keeping these parameters constant, one can crank up the ISO and move the histogram to the right, but exposure is not changed.

A certain amount of exposure is necessary for acceptable image quality. With an ISO-less sensor, once the required shutter speed and f/stop are selected one can leave the ISO at base and adjust the brightness of the rendered image with the "exposure" control in the raw converter (see the excellent post by Emil Martinec). This approach gives better highlight headroom. However,  it is difficult to determine the optimal shutter speed and f/stop at base ISO, since there is no way to evaluate the noise level in the image. With my D800e, ISO 3200 gives acceptable image quality in challenging situations, and in these situations I often set the ISO to 3200 and use the histogram to juggle between the shutter speed and f/stop. Once this exposure is determined, one could drop back to an ISO where the camera is ISO-less (perhaps ISO 400 for the D800e), but then the LCD preview is dark and chimping is fruitless. Personally, I leave the ISO at 3200 but would be interested how others handle this situation.

Regards,

Bill

[Torbjörn Tapani]

On the D800E in that situation I would use ISO 1250 and then push in post. This was chosen after talking to Jim Kasson about shadow s/n, unity gain and isolessness. You can find it on the forum somewhere.

[Bart_van_der_Wolf]

On the D800E in that situation I would use ISO 1250 and then push in post. This was chosen after talking to Jim Kasson about shadow s/n, unity gain and isolessness. You can find it on the forum somewhere.

Hi,

Nothing beats the image quality of real exposure, i.e. photons as a product of intensity x time (I x seconds). This usually maximizes the Dynamic range of a sensor, by fully utilizing the well depth or saturation capacity of the sensor, and minimizing the read-noise + low exposure photon shot noise levels and gain amplification.

However, if one 'must' underexpose, then there is usually a sort of sweetspot between ISO 800 and ISO 1600 where the Signal to Noise Ratio that one can achieve (for an underexposed shot !) is balanced with the reduced dynamic range caused by the underexposure.

But boosting ISO is not really changing exposure (I x seconds), so it's not usual to talk about ETTR at anything above base ISO.

Cheers,
Bart

[AlterEgo]

I agree 100% here, but when practicing ETTR we have a conundrum: we are using the histogram to  evaluate exposure, but the histogram by itself does not indicate exposure. Exposure is the amount of light falling on the sensor and (for the technically oriented) is measured in lux seconds. For a given illumination and subject reflectance, exposure is determined by the shutter speed and f/stop. Keeping these parameters constant, one can crank up the ISO and move the histogram to the right, but exposure is not changed.

A certain amount of exposure is necessary for acceptable image quality. With an ISO-less sensor, once the required shutter speed and f/stop are selected one can leave the ISO at base and adjust the brightness of the rendered image with the "exposure" control in the raw converter (see the excellent post by Emil Martinec). This approach gives better highlight headroom. However,  it is difficult to determine the optimal shutter speed and f/stop at base ISO, since there is no way to evaluate the noise level in the image. With my D800e, ISO 3200 gives acceptable image quality in challenging situations, and in these situations I often set the ISO to 3200 and use the histogram to juggle between the shutter speed and f/stop. Once this exposure is determined, one could drop back to an ISO where the camera is ISO-less (perhaps ISO 400 for the D800e), but then the LCD preview is dark and chimping is fruitless. Personally, I leave the ISO at 3200 but would be interested how others handle this situation.

Regards,

Bill

for your ISO-less camera you decide about exposure (expsoure time and aperture) based on the scene/subject to maximize it (@ "base" ISO) and then you might want to dial the gain with other considerations in mind (like if you still do not approach to the clipping where you want to have details or linearity near clipping, etc, etc), what is so difficult ?

the origins pushing up to ISO1250 are here = http://blog.kasson.com/?p=6544

and no - we are not using useless histograms - we use in frame zebra/blinkies.

[texshooter]

Where shooting conditions do not allow adjustment of shutter or aperture it is better to ETTR using ISO (most modern sensors) than to ETTM and boost shadows in post.

This blogger makes a strong case to the contrary...

http://chromasoft.blogspot.com/2009/09/why-expose-to-right-is-just-plain-wrong.html

Using ISO (only after exhausting One's shutter and aperture options) is --I think all would agree-- best to achieve a histogram that is acceptable. By acceptable, I mean exposed for middle gray.   What seems to be under contention is the last extra step of ETTR by increasing ISO.  I can't seems to find unanimity on this one. Some say it depends on the sensor, some say it depends on your ISO range, some say it should never be done, and some always do it. Which is it!

[Torbjörn Tapani]

No that blogger confuses iso with exposure. Didnt read all of it. Not worth it.

[Jack Hogan]

Using ISO (only after exhausting One's shutter and aperture options) is --I think all would agree-- best to achieve a histogram that is acceptable. By acceptable, I mean exposed for middle gray.   What seems to be under contention is the last extra step of ETTR by increasing ISO.  I can't seems to find unanimity on this one. Some say it depends on the sensor, some say it depends on your ISO range, some say it should never be done, and some always do it. Which is it!

If your objective is maximum IQ (the quantitative variety, i.e. SNR, DR, etc. in the raw data) then after maximising exposure at base ISO subject to artistic constraints without blowing desirable highlights - assuming your camera is well behaved (most are) you should only raise ISO if it gets you better SNR in the shadows etc.  Otherwise don't: raising it would only limit potential DR.

How do you know whether raising ISO at a fixed exposure gets you better SNR in the shadows?  Know your camera, or alternatively peruse data at DxO, Jim Kasson's, Bill Claff's.  A good first indication is whether input referred read noise drops as ISO is raised.  When it stops dropping meaningfully, stop raising ISO.  For instance most Exmor-sensored cameras stop improving meaningfully after the first few ISO stops.  Examples in the earlier link.

Jack

[EricV]

... after maximising exposure at base ISO subject to artistic constraints without blowing desirable highlights ... you should only raise ISO if it gets you better SNR in the shadows ...

  If there is no artistic constraint other than maintaining highlight detail, then after maximizing exposure at base ISO, there is no room to increase ISO.  Putting it another way, if you can raise ISO without causing blown highlights, then you have not yet maximized exposure, and as discussed earlier you should do that first.  If there is an artistic constraint which forces you to limit exposure (shutter speed constrained by motion blur, aperture constrained by depth of field), then raising ISO can be helpful.

[Jack Hogan]

  If there is no artistic constraint other than maintaining highlight detail, then after maximizing exposure at base ISO, there is no room to increase ISO.  Putting it another way, if you can raise ISO without causing blown highlights, then you have not yet maximized exposure, and as discussed earlier you should do that first.  If there is an artistic constraint which forces you to limit exposure (shutter speed constrained by motion blur, aperture constrained by depth of field), then raising ISO can be helpful.

Sure.  Think indoor sports, for instance hockey.  You have aperture as open as possible, limited by sharpness/DOF constraints, say f/2.8. Shutter speed needs to be 1/400 or faster to freeze players.  The helmet is the brightest object in the frame that you care to see some detail in and at base ISO it is 3 stops down from clipping in the raw data.  Do you raise ISO?

[mouse]

Sure.  Think indoor sports, for instance hockey.  You have aperture as open as possible, limited by sharpness/DOF constraints, say f/2.8. Shutter speed needs to be 1/400 or faster to freeze players.  The helmet is the brightest object in the frame that you care to see some detail in and at base ISO it is 3 stops down from clipping in the raw data.  Do you raise ISO?

Certainly; that's what ISO was designed for.