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Expose To The Right (ETTR)
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  • Quite right!

    And the whole idea of exposing to the right works very well with RAW only, it's all about maximizing the use of the DR (the range between the saturation level of the photo sites when shooting and the noise floor) of the sensor and later adapt it to the target display in post.

    Our main problem, even with the hacked GH2, is 8 bit. You can't squeeze a high DR into 8 bit and expect to stretch detail again in post where you want it and squeeze other parts to balance for the limited range of our displays (TV has only about 5 stops in an ordinary viewing environment and public cinema can show about 9). But most sensors can exceed 10 stops these days, the best ones go close to something like 14 (Arri Alexa).

    We have no other possibility than adapting our look while we shoot as close as possible to the range of the target medium, since any massive corrections in post starting from 8 bit will inevitably introduce more banding. So, using the 'famous' Technicolor Picture Style with a 5D is pretty much useless for a scene with low contrast and it can introduce banding in post even with contrasty scenes if you don't like the milky look it delivers.

    This applies to any camera with less than 10 bit of recording.
  • @bdegazio
    OK, I get what you're saying. So his tests were about noise, where there's no advantage, whereas the real issue is the variety of colours and chroma available for each stop in the frame. I'd love to see a test as thorough as the above article, but with colour levels - a real world (yet scientific) test!

    @nomad Is it not true that it should work with 8 bit as well as with 12 bit. The number of available levels is already reduced, but accessing more (in the brighter end of the histogram) makes sense, no? (Perhaps with 12 bit, it could be said to be less relevant, as there are so many more levels within every stop to begin with.)
  • ChromaSoft blog: "[In Nikon lossy-compressed NEF files,] raws have 683 codes versus the 4096 to 16384 that uncompressed Nikon raws have."

    Taken at face value, this statement implies that the bit-depth of compressed NEF files has been truncated from the original 12-bit or 14-bit RAW image sensor data down to less than 10 bits. If that were in fact the case, I would no longer regard the data as RAW, but as mutilated. What is actually done is to map the original linear curve into a near-logarithmic curve that is closer to how the eye perceives color.

    http://www.openphotographyforums.com/forums/showthread.php?t=5499

    Based on that quoted statement alone, I would be highly skeptical of the objectivity of any technical claims made by this author.

    In addition, @bdegazio is correct in pointing out that the author's tests reveal virtually nothing about color depth - they show only the difference in signal/noise ratio at different ISO settings on one particular camera (a Canon G10).

    For good examples of how ETTR can be effective in the right shooting conditions, I found this article informative:

    http://schewephoto.com/ETTR/index.html
  • OK. I completely get it. I'm on board. I now also understand why, LPowell, you have mentioned several times in the GH1 hack threads that high exposure is more likely to cause high data rates and hence crashes - the big data capture is all pressed up to the right.

    For a few years I had a 5D Mk1 that I absolutely LOVED for RAW stills work, and I have one image that I always regarded as supreme, above all others I've taken, that I always show to demonstrate the brilliance of the camera (with a Zeiss 50mm) - I just checked in Aperture (an awesome Apple app. by the way) and yup, the master file is WAAAY over-exposed, with what appears to be blown out highlights, but on the adjusted version, it's simply perfect. I have a real world verification of something that isn't placebo, or too subtle to notice but simply better.

    So, LPowell, would you agree that ETTR has a place in 8 bit acquisition? It seems even more so than in RAW, to me.
  • ETTR is like walking on thin ice :)

    When it works, it works great... I guess. Otherwise... hehe.
  • @LucasAdamson - "would you agree that ETTR has a place in 8 bit acquisition?"

    Yes, the fewer bits you have to work with, the more important it is to make optimal use of them.
  • @stonebat Sure, but it's good to know - like it's good to know not to ever expose to the left, I mean. I wouldn't have known that necessarily, and it's pretty important if you've only got 8 bit depth.

    @lpowell Much obliged for your clear explanations and clarifications, as well as your top notch hacks! Thank you!
  • I think ETTR explains why highlight roll-off can be a good thing. Often 8-bit depth won't give enough DR. Then we gotta decide either overexpose or underexpose. I prefer slight overexposure if ISO can stay low enough. That feels like walking on thin ice :)
  • Let me get this straight.

    So, I'm shooting outside on an overcast day. I have my camera set to ISO 100, and the histogram is showing a small dynamic range, low contrast shot, in the middle of the scale.

    I 100% agree that getting the histogram to register the scene to the right makes sense, but raising ISO to get there? Not quite fully convinced yet. Those tests you posted @LPowell, were shutter speed adjusted stills and the author did not compare with ISO bracketed shots, which might be used in video.

    This theory came from photography, where there is a choice of 3 exposure variables to adjust - aperture, shutter speed & ISO, whereas in video, generally speaking we only have the two - aperture and ISO, with shutter speed best left where it is for the most part. In photography, shutter speed would be the most obvious choice to me for ETTR, but the results will inevitably be compromised if ISO is used for bracketing, and ISO is commonly used for exposure control in DSLR video.

    So if my hypothetical shot has nothing in the top stop (half of all available levels!) and I need to expose in that area (and I agree that I do), will raising ISO to get there really help me out at all? This is still unproved to me with the tests posted (though I don't doubt it could be - it seems feasible.).
  • I'd determine aperture and shutter speed. Then ISO varies up to a limiter. Comfortably up to 800. Maybe 1250.

    But I don't want to stick to ETTR all the time. Sometimes it's nice to do underexposing to give a proper mood.

    Even if there is enough lighting to keep ISO low, sometimes the source clips still look crappy. I think that's when ETTR can shine.
  • @LucasAdamson - "So if my hypothetical shot has nothing in the top stop (half of all available levels!) and I need to expose in that area (and I agree that I do), will raising ISO to get there really help me out at all?"

    Increasing ISO will of course increase noise as well. When shadow detail is a high priority, I'm willing to tolerate a bit more noise to get it. But if I'm planning on crushing the blacks for a high contrast look, I'll favor the highlights instead.

    As @stonebat suggests, I first set aperture and shutter speed (typically 1/60). How far I'm willing to push ISO depends on the camera. The GH1 was fine up through ISO 400. Beyond that, I'd make a judgment call - drop the shutter down to 1/30 if not too much motion blur, and/or raise ISO up to 800 and deal with noise reduction in post. The GH2 looks good up through ISO 800, and 1600 is acceptable if necessary. On my Nikon D5100, I can take ISO up to 1600 without noise issues, and as far as 3200 max. Each camera has its own particular strengths and weaknesses.
  • Guys, sorry for the silly question, but I've never really much used anything other than standard and I've been using lighting / reflectors to control DR, together with making adjustments in post.

    Last night I was attempting to shoot the moon through a telescope and using various other lenses, and it was varying quite a lot as the clouds passed in front of it (nice effect though). Because the brightness was going up and down I simply couldn't arrive at an exposure which worked at both "ends" of the scale, ie to show the details on the bright surface when there weren't any clouds, and at the other end, to show the dim moon with the clouds around it, lit up. That's a scenario with a huge dynamic range, and I discovered that because I couldn't capture the extremes well, it was pretty much impossible to do anything with the images afterwards.

    So are there good in-camera settings that give a bit more highlight / lowlight compression for contrasty subjects so you can get the best out of the 8 bits available? I know, I can experiment, but some of you must be more familiar with the various presets on the camera than I am and I was hoping you could suggest what to try.

    The one good thing about my Canon XHA1 was its comprehensive menus for highlight and lowlight compression but because the GH2 is so good anyway, I haven't particularly had issues with using Standard up till now. And unfortunately the moon scenario isn't one I can control with lighting or reflectors!
  • "Smooth" and "Nostalgic" will give you lower in-camera contrast to compress that scene, plus you can dial down contrast to minimum (-2).

    But, as I tried to explain above, only do that for hi-con scenes.
  • @LPowell, I have an upcoming short, shooting on GH1s with Peak Reliability patch (thanks btw) for a film we want to be b&w. Would shooting in camera B&W improve levels of chroma available, or just reduce bitrate?
  • @nomad Thanks - I'll give that a go. Useful to have this as a starting-point because once you're in the dark and cold, it's tricky to play around with menus.

    Cheers!
  • @LucasAdamson
    In B&W film mode, the AVCHD encoder will store minimal data in the two chroma channels and record the luma channel as usual.
  • Ah, so just lower bitrate then - no advantage in terms of luminance (yes I said chroma by mistake) levels. Thank you again. I'll shoot in colour then.
  • Exposing to the right is great when it's great. If you're trying to keep blue sky color, or any number of different scenarios, it's bad blanket policy. Best to say it's 'often' a good idea. Expose for what's best for the shot you're composing.
  • I love this comment on that article: "I have learned to expose the subject right."
  • @hishimaru
    The Online Photographer blog: "These days, noise is really not a big source of image quality loss..."

    Talk about bullshit. I almost stopped reading right there. Then comes the next paragraph:

    "The thing is, digital behaves like slide film..."

    LOL, if only it did!
  • Well it certainly does as far as exposure is concerned. With digital just like with slide you expose for the highlights and fill for shadows. With negative you expose for shadows and develop for your highlights.
  • @dkitsov
    Regardless of how you expose it, a digital image sensor has a linear response to light, while film is logarithmic. That's why the author's claim is "bull".
  • Well, as a general rule, I do think usually about saving highlights shooting video, same as we used to do with Kodachrome, etc. You can pull up noisy blacks but you can't usually pull back blown whites.
  • When a camera's DR can't cover entire range, gotta crush black and/or roll off highlight. I guess that's another walking on thin ice, too.

    In that case I'd prefer highlight roll-off if ISO can stay low enough. Especially daylight. I might lose some highlight detail if it clips just little... but it's ok to me. That might crush black to avoid extreme clipping. That's ok, too.