Luminous Landscape Forum
Equipment & Techniques => Digital Cameras & Shooting Techniques => Topic started by: Rory on November 09, 2014, 11:41:59 am
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Further to the discussion on the optimum digital exposure, I would like some help on a specific case. Photographing birds with white feathers often presents the situation where the feathers can be extremely bright when at specific angles to the sun and images with blown feathers are suboptimal. The following example was shot with a 7DII, 600mm + 1.4X in manual mode at f/5.6, 1/1600 sec and ISO 800. Light conditions were changing continuously and the subjects were hopping about with considerable energy. I was adjusting the shutter speed and ISO on the fly, basically winging it (bird metaphors fit I guess :*)).
Here is the full frame of the image from DPP 4:
(http://roryhill.zenfolio.com/img/s7/v158/p30161555.png)
Zooming in to show the feather blowout. As you can see, a small portion of the feathers do not have any detail, although I have pulled the highlight slider down in DPP.
(http://roryhill.zenfolio.com/img/s7/v157/p115297013.png)
I used DPP, with as shot settings (all noise reduction turned off) to convert the image to a TIF and rendered in Lightroom, where I also adjusted the highlights. As you can see, there is still some blown highlights.
(http://roryhill.zenfolio.com/img/s6/v144/p303550920.png)
Since Adobe has yet to release ACR for the 7DII it could well be that the DPP rendered TIF is insufficient to allow LR to render detail in the highlight area. To try to determine if this was the case, and to check if I had over exposed, I took a look at the image in Raw Digger, which also suggests that there is some blowout according to the OvrExp indicator. I am a little confused here, as the max for the G and G2 channels is 13,256. Is this the max for the 7DII? I thought it used 14 bits which would be around 16,000.
(http://roryhill.zenfolio.com/img/s6/v141/p402836689.png)
The red channel looks better.
(http://roryhill.zenfolio.com/img/s6/v138/p316435612.png)
Here is the Raw Digger histogram for the entire image:
(http://roryhill.zenfolio.com/img/s12/v180/p117796877.png)
Here I have selected the portion of the image where most of the over-exposure is occurring:
(http://roryhill.zenfolio.com/img/s5/v130/p519809018.png)
And here is the histogram for the selected portion, where I can see the blowout in the green channels.
(http://roryhill.zenfolio.com/img/s7/v166/p96046171.png)
Hopefully I still have your attention at this point. :)
- Is this image over-exposed or do you think it is possible to render some detail for the brightest feathers?
- If the image is over-exposed, how would you recommend metering to avoid feather blowout?
Thanks
Rory
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I think I can answer one of my questions, about why clipping occurs at 13,256. I think Canon changes the clipping depending on the ISO, and in this case the ISO was 800.
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Bracketing has saved my bacon on many a bird shot.
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Whenever possible I'll take a few test exposures and check the histogram for any overexposed channels, adjusting exposure (manually) as required. Doesn't work too well for tiny stuff jumping in & out of light unless you decide which light is the one you want and wait for the bird to jump into your chosen light.
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Bracketing has saved my bacon on many a bird shot.
That's a great idea. I've been thinking about it. Turning it on and off seems a little clumsy in the Canon bodies. Is there a trick?
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Whenever possible I'll take a few test exposures and check the histogram for any overexposed channels, adjusting exposure (manually) as required. Doesn't work too well for tiny stuff jumping in & out of light unless you decide which light is the one you want and wait for the bird to jump into your chosen light.
That is what I normally do but I usually end up with significant under-exposures. This was not such a big deal when I'm shooting Nikon with the D4 or D800E, but with the 7DII I'm finding that you have to try to eke out all the ETTR possible. I'll have to take a look at the exposures on a number of my shots to see if there is some type of sunny f/16 type rule I can use. It gets tricky with changing ISO, since the exposure ceiling drops as the ISO goes up.
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Perhaps the 7DII isn't optimum for this task.
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Place a white feather in various lighting conditions that occur when you shoot and acquire a series of exposures at various ISO - see which combination of ETTR and raw converter gives you the latitude you require to balance your exposure parameters and still maintain/reclaim your highlight detail.
I am finding more and more nowadays that, for specific exposure issues like yours, exposure is as much determined by the destination for raw conversion as it is by the camera itself.
In the end, you may just have to expose for the extreme highlights if they are that important and let the rest of the tonal range fall where it will, remapping it in post. One advantage of having white feathers blow out is that, if there are still detail data left in the red and blue channels, you can reconstruct the highlight data by placing the good channel into the blown channels at the same tonal level, keeping the white neutral (R=G=B) and reintroducing detail.
kirk
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Thanks Kirk. I agree - testing is in order. Good idea about the feather.
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Rory, great post!
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Hi Rory,
Use "Logarithmic" scale on the Y-axis and things will be more clear.
This info may also be useful: https://www.youtube.com/watch?feature=player_embedded&v=NdLjU70xhdQ
I may add that I don't shoot a lot of birds, but I also feel they are a difficult case. I may also add that I don't foresee giant steps on the sensor side. They are decently close to physical limits. Making them larger helps a bit, but than you need a longer lens. Twice the sensor diameter, half the noise and eight times heavier lens. To that comes the $s.
Best regards
Erik
Ps. Well, there are rumors about non Bayer sensors, from Sony and Canon, and they may be more efficient.
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Thanks Erik. Very informative.
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Here is an example of a specular effect which looks odd. With higher DR, this would have been ok. If you look at the rear leg, it has some water droplets which blew out in the sunlight. Since the bird was walking forward following prey, bracketting would not get the legs atthesame angle.
The top is cropped, otherwise as shot.
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ETTR makes sense when there is something to gain in terms of noise. This usually happens in medium and high contrast scenes. With a modern sensor and under these situations (low DR scene compared to sensor's DR), trying to achieve ETTR is a risky business and moreover useless.
Always leave some highlight headroom by applying negative exposure compensation as a regular basis, no matter if your JPEG displays a bit dark or you need to push exposure in the RAW developer a bit. Your sensor can deal with that shadows noise, your highlights will be preserved, and in addition you'll be able to shoot faster!.
ETTL era? ;D
This is how a not so new APS-C camera (Pentax K5) behaves when 6 stops of underexposure are applied in a low DR scene:
(left camera JPEG, right RAW+6EV in pp)
(http://www.guillermoluijk.com/article/perfect/antesdespues1.jpg)
RAW histogram of the previous capture:
(http://www.guillermoluijk.com/article/perfect/histraw.gif)
Of course this is an extreme example and some parts in the jacket had a far from desired SNR. I'm talking about 1-1.5 stops of underexposure vs perfect ETTR.
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This is how a not so new APS-C camera (Pentax K5) behaves when 6 stops of underexposure are applied in a low DR scene:
indeed... sized for a social media.
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I took a look at the image in Raw Digger, which also suggests that there is some blowout according to the OvrExp indicator. I am a little confused here, as the max for the G and G2 channels is 13,256. Is this the max for the 7DII? I thought it used 14 bits which would be around 16,000.
Rory I found similar results with a Canon 600D some time ago. It seems to me that the clipping level of the ISO amplifier following the sensor is somewhat lower than the maximum input level that the A/D converter can handle. Hence the clipping point is somewhat lower than 16,384 which would correspond to the A/D converter's maximum input. Not sure why there would need to be such a large margin but I dare say there is a reason.
You certainly have some clipping there in the raw file but I wonder whether ACR will be able to do something with it. I've read that under certain circumstances, actual clipping like this can be recovered in ACR by the use of some smart algorithms. I draw a distinction here between actual clipping and clipping in the camera developed jpeg which seems to set a white point that gives a safety margin, and this can be readily recovered in ACR because the raw signal isn't actually clipped.
Dave
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You certainly have some clipping there in the raw file but I wonder whether ACR will be able to do something with it. I've read that under certain circumstances, actual clipping like this can be recovered in ACR by the use of some smart algorithms. I draw a distinction here between actual clipping and clipping in the camera developed jpeg which seems to set a white point that gives a safety margin, and this can be readily recovered in ACR because the raw signal isn't actually clipped.
Dave
I was able to improve it slightly with ACR but ended up doing a little cloning as well to make it look natural.
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Not reaching the end of the ADC bit scale in the RAW data is common. The Canon 5D used to clip at 3692 rather than 4095. That's a fairly good amount of levels wasted* for a 12-bit camera (and yet we have to add the non-zero bias offset typical from Canon).
(http://www.guillermoluijk.com/tutorial/satlevel/hist5d.gif)
* But probably only cameras that do so can enjoy the whole DR of the photosites, while others saturate the ADC input signal losing (a bit of) highlights information instead. I see clipping occurring at this initial stage as a reduction of the effective full well capacity of the sensor.
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Not reaching the end of the ADC bit scale in the RAW data is common. The Canon 5D used to clip at 3692 rather than 4095. That's a fairly good amount of levels wasted* for a 12-bit camera (and yet we have to add the non-zero bias offset typical from Canon).
(http://www.guillermoluijk.com/tutorial/satlevel/hist5d.gif)
* But probably only cameras that do so can enjoy the whole DR of the photosites, while others saturate the ADC input signal losing (a bit of) highlights information instead. I see clipping occurring at this initial stage as a reduction of the effective full well capacity of the sensor.
Is there any real reason for this? Such as preventing blooming in nearby pixels? Surely a large matrix meter could set the exposure to 99% at the brightest metered spot of the frame?
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Just yesterday I had a look in RawDigger at some files from my Nikon D610. For ISO values from 100 through to 800, the clipping point (in the green channel) was the same at 15,780. At ISO1600 it rose to 16,273. These values are quite close to the maximum for a 14 bit A/D converter (16384).
This suggests to me that the components in the sensor (photosites, amps, A/D converters) are all well matched.
The fact that the clipping point doesn't change from ISO100 to ISO800 suggests to me that the full well capacity of the photosites is a bit higher than the amp clipping point.
Dave
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Perhaps the 7DII isn't optimum for this task.
The 7DmkII has a great AF system with 65 all cross type sensors, fast processing and high frame rate which makes it great for the job. This is where the whole debate about quality of the senor subsystem comes into play. In controlled conditions, not usually a big issue, in constantly changing conditions where speed is important, it can make or break the shot. In reality the DR, Color Depth and ISO performance of a sensor matters a lot because it is the ceiling on performance and it will never, ever get any better.
I also agree that each conversion engine is going to handle things differently enough that one will handle this situation much better than others. However, I'm more the learn one and know it well, than trying to juggle 3 or 4 different conversion processes type of person.
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I may also add that I don't foresee giant steps on the sensor side. They are decently close to physical limits.
Sensor seem close to physical limits as far as the quality of the signal coming out of the photosites, but there is still significant room for improvement (particularly at Canon) in minimizing noise from later stages of the processing pipeline, so that Guillermo's ideal of "ETTL" could be pursued. When the most exposure you can get to the sensor is short of blowing out any photosites, the only important constraint on choice of ISO speed setting should be avoiding amplifying any highlights into clipping; one should not have to worry about a too low ISO exposure index choice leading to further degradation of shadows beyond the noise already present in the photosites. That is, the ISO speed setting should some day be reduced to a convenience, indicating the intended level placement for the conversion from raw. Already, with some sensors it seems that any speed setting beyond about ISO 400 might as well be done with no further amplification of the analog signal or in the raw file levels, but just in conversion from raw to JPEG (or whatever final display format is used), a flag in the raw file to indicated the intended default conversion level (including display on the rear-screen or EVF.) Even super-fancy multi-million-point light metering could ideally just record information about the maximum pixel level in the raw file, rather than committing to the accuracy of that reading through extra amplification of raw levels.
... Making [the sensors] larger helps a bit, but than you need a longer lens. Twice the sensor diameter, half the noise and eight times heavier lens. To that comes the $s.
As you say at the end, for birding and other telephoto cases, this is in fact almost entirely about lenses that gather light faster, not larger sensors. More precisely, the most fundamental physical constraint on low light handling is entrance pupil diameter: focal length divided by aperture ratio. A 36x24mm "35mm format" sensor with a 600/4 lens is great for birds, but as far as shadow handling, probably a 24x16mm "APS-C" sensor with 400/2.8 lens or a 17.3x13mm "Four Thirds" sensor with 300/2 lens would be as good, due to the huge 150mm entrance pupil diameter in each case -- and the lenses would be about as heavy and expensive too!
My guideline is that when the user of a format would benefit from a prime faster than about f/1.4 to f/2 or a zoom faster than about f/2.8, that is when a larger sensor format starts to offer a low-light handling advantage, through the easier optical design of longer lenses of the same entrance pupil size.
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That's a great idea. I've been thinking about it. Turning it on and off seems a little clumsy in the Canon bodies. Is there a trick?
The Q-button: Unless you move to another section the bracketing section will stay for the next press of the Q-button and you just turn the wheel next to the shutter button to turn off bracketing. The other way is to have two identical settings as C1 and C2 except for bracketing. If C1 is with bracketing then turn to C2 to get off bracketing. It's very quick. But also if you underexpose but e.g. 1 stop you can adjust in pp. no problem. I also would expect the overexposure you saw not to be a problem if you use Lightroom when the RAW format is supported.
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The Q-button: Unless you move to another section the bracketing section will stay for the next press of the Q-button and you just turn the wheel next to the shutter button to turn off bracketing. The other way is to have two identical settings as C1 and C2 except for bracketing. If C1 is with bracketing then turn to C2 to get off bracketing. It's very quick. But also if you underexpose but e.g. 1 stop you can adjust in pp. no problem. I also would expect the overexposure you saw not to be a problem if you use Lightroom when the RAW format is supported.
Thanks Hans. I subsequently figured out the C1/C2 thing, but I'll also try using the Q-button which is a very nice implementation by Canon.
Unfortunately Lightroom, although pretty good, is not good enough to pull the detail back. It's a regular problem for us bird shooters and I usually nail the exposure, but it is tougher with the Canon than the newer Nikons.
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Thanks Hans. I subsequently figured out the C1/C2 thing, but I'll also try using the Q-button which is a very nice implementation by Canon.
Unfortunately Lightroom, although pretty good, is not good enough to pull the detail back. It's a regular problem for us bird shooters and I usually nail the exposure, but it is tougher with the Canon than the newer Nikons.
I had the old 7D and I looked at some shots I did back in 2010. The lens was the Canon 500 f/4L IS with the Canon 1.4x TC III at f/5.6, ISO 800, 1/1600s. Attached Rawdigger screen shot and edited version and default Lightroom settings at 1:1 view. I have not tried the 7D mkII, but would expect the results to be better. I sold the 7D off again as I was more happy using my 1Ds mkIII for bird and animal shooting despite the lower pixel density.
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I had the old 7D and I looked at some shots I did back in 2010. The lens was the Canon 500 f/4L IS with the Canon 1.4x TC III at f/5.6, ISO 800, 1/1600s. Attached Rawdigger screen shot and edited version and default Lightroom settings at 1:1 view. I have not tried the 7D mkII, but would expect the results to be better. I sold the 7D off again as I was more happy using my 1Ds mkIII for bird and animal shooting despite the lower pixel density.
I can find examples where Lightroom does pull back the detail too Hans. That does not help for the cases where it can't. The way feathers reflect light is extremely variable. I usually manage to get the exposure the way I want - but not always.
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I can find examples where Lightroom does pull back the detail too Hans. That does not help for the cases where it can't. The way feathers reflect light is extremely variable. I usually manage to get the exposure the way I want - but not always.
You can, of course, also download the Adobe DNG 8.7RC converter and check your images.
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You can, of course, also download the Adobe DNG 8.7RC converter and check your images.
That is helpful for those that do not have an up-to-date Lightroom or Photoshop. The latest version of Capture One is also very good at highlight recovery.
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That is helpful for those that do not have an up-to-date Lightroom or Photoshop. The latest version of Capture One is also very good at highlight recovery.
Ok, did you redo the original images you showed in the beginning post then?
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Ok, did you redo the original images you showed in the beginning post then?
Yes I did Hans. Lightroom/ACR could not recover all the blowout.
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Yes I did Hans. Lightroom/ACR could not recover all the blowout.
Uhm, just surprised you didn't show the results given the long intro post where you were looking for help. But fine, end of story.
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Uhm, just surprised you didn't show the results given the long intro post where you were looking for help. But fine, end of story.
Sorry about that Hans. I got similar results with the updated LR from the raw file as I did with the original TIFF and LR 5.6. I mentioned this in passing in post 16. The red and blue channels just did not have enough info. I guess I should have shown this, but by that time I was more interested in the "how to get the exposure right" part of the equation. Your suggestions about using the Q-button and C1/C2 for bracketing are much appreciated.
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Rory, any follow-up on your chickadee problem? I would like to know, because my favorite winter subject is another dark-and-white bird, the Bald Eagle. How's the 7D2 doing, BTW?
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Rory, any follow-up on your chickadee problem? I would like to know, because my favorite winter subject is another dark-and-white bird, the Bald Eagle. How's the 7D2 doing, BTW?
Hi Nancy - happy new year!
My first 7D2 was a dud, with inconsistent focus. My second body is great. The focus is extremely accurate, with quick acquisition and tracking. Here is a recent example (larger size (http://roryhill.zenfolio.com/img/s10/v104/p2226896.jpg)):
(http://roryhill.zenfolio.com/img/s10/v104/p2226896.jpg)
There is no easy answer to the feather blowout issue. It has not been quite the issue with the Nikons I have shot with, but with the 7D2 you basically have to shoot, look at the playback at 100% and go from there. I do have some rule of thumbs based on getting an exposure for bright blue sky. Normally I would over-expose the sky by +2EV, but depending on the brightness of the white feathers I would shoot at -1EV to +1EV of the bright sky. In this case I exposed at 0EV bright sky reading. I decided to let the backlit portion blowout as I could not capture the whole DR. Larger size (http://roryhill.zenfolio.com/img/s10/v111/p290701618.jpg).
(http://roryhill.zenfolio.com/img/s10/v111/p290701618.jpg)
Some birds white feathers are brighter than others. For example, the neck of a Belted Kingfisher or the breast of a Common Merganser are extremely bright. Bald Eagles are more of a medium brightness and it is usually easy to bring back detail unless you are dealing with a back or oblique side lighting issue.
In this example of a Horned Grebe, the lighting was consistent and I was able to do some test shots for the brightest feathers and then just stuck with that exposure, which was 0EV on bright sky. Larger size (http://roryhill.zenfolio.com/img/s6/v151/p743577109.jpg).
(http://roryhill.zenfolio.com/img/s6/v151/p743577109.jpg)
Here is a Bald Eagle shot in mid-morning light which was pretty easy to expose at about +0.5EV bright sky. Larger image (http://roryhill.zenfolio.com/img/s6/v138/p461293272.jpg).
(http://roryhill.zenfolio.com/img/s6/v138/p461293272.jpg)
I took all these images in the last week with the new body.
Hope this helps. As I mentioned in my original post the problem with birds where the brightness of the feathers changes quite radically as the angle of the light changes. In general, Bald Eagles do not have this issue.
Cheers
Rory
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If you are using ACR or LR, have you tied the "camera neutral" profile? This gives you (mostly) the linear numbers coming off the sensor, and without a tone curve applied that would otherwise exaggerate the highlights. It won't "unblow" blown highlights, but it will give you the maximum headroom that your sensor afforded it. It is a good place to start with the highlight enhancements if nothing else, and often can save the day.
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If you are using ACR or LR, have you tied the "camera neutral" profile?
Yes
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With Ektachrome 64 we had 2.1 EV above neutral gray before the highlights lost detail.
Do some basic tests and check the images carefully. Looks to me you are over analyzing it.