"Exposing to the right" is over exposed, what now?
in [Photoshop]
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From: Mike Russell on 7 Oct 2009 00:30 On Sun, 4 Oct 2009 17:25:57 -0700 (PDT), Porte Rouge wrote: > Wow, good stuff. I had to run out and get my camera and check the > settings. I don't understand what he says about the white balance. I > have it set on auto and have ignored it when shooting RAW. Should I > adjust it for each lighting condition when I shoot and this will give > me a truer histogram? Setting a more correct white balance may give a more accurate histogram, but this is relying too much a coarse measurement. When in doubt, give up another half stop or more past the point where the "blinkies" stop, or bracket your exposure as insurance against blown highlights. -- Mike Russell - http://www.curvemeister.com
From: Floyd L. Davidson on 7 Oct 2009 01:50 "Charles" <charlesschuler(a)comcast.net> wrote: >> Digital clipping is almost never "saturation of the >> sensor". Unless you are shooting at the base ISO >> clipping is saturation of the Analog-Digital-Converter >> (ADC) by sensor output that is greater than the maximum >> ADC input. > >And what difference would that make? The statement was that digital clipping was due to saturation of the sensor. The fact is, it's not. And note that if it were there would be a significantly different set of characteristics to apply, the ADC does saturate with the mathematical precision you note below, while the analog electronic sensor does not. >There is no sharper knee than one >imposed by basic mathematics. 2^8 = 256, is a simple example. With 8 bits, >the maximum value is 255, base 10, with NO exceptions possible. You >actually help to make the case that over-exposed digital shots guarantee >lost information in the bright portions of the scene. Nobody with an ounce of understanding would deny that, so why do you find it worth noting that I 'actually help' make that case? Of course I did! >I continue to believe that exposing to the right is perpetuated by folks >with limited experience and knowledge. They are perhaps into the dark parts >of scenes and don't understand dynamic range. Many of us are more greedy >and want details at both ends of the luminosity range. You must not understand dynamic range then, given that statement! The entire concept of "Expost To The Right" is based on maximizing captured dynamic range. It is *precisely* a way to get maximum "details at both ends". >Hey, blow those high-lites out! If that is the intended message of a given >scene, go for it. I don't care for over-exposed shots ... they are just not >my thing. I have seen some high-key shots that were attractive and >effective and do appreciate the skill and art of the photographers who can >pull that off. > >Specular high-lites might deserve to be blown out. Not the point of my >response. I'll just say it one more time and then go away ... if it is >clipped (by a sharp knee response curve ... due to sensor saturation or A/D >saturation or any saturation link in the chain) it is GONE! Gee whiz, that's like arguing that rocks are "hard". And of course that is exactly why people use the Expose To The Right method. -- Floyd L. Davidson <http://www.apaflo.com/floyd_davidson> Ukpeagvik (Barrow, Alaska) floyd(a)apaflo.com
From: Paul Furman on 7 Oct 2009 11:25 John Sheehy wrote: > Porte Rouge wrote > >> I set my exposure to slide the histogram to the right, without clipping >> ( when I have time), to capture the most tonal levels . So, now when I >> am editing the photos they are over exposed(not clipped). A sunrise is >> a good example. The deep colors are washed out. The obvious fix(to me >> anyway) in Lightroom or CS4 is to reduce the exposure. Now my question >> is, by reducing exposure in post, am I just ending up in the same place >> (histogram to the left) as if I had just ignored the histogram when I >> was shooting and set the exposure to properly expose the image using >> my light meter? I guess in short I am asking if Lightroom or CS4 loses >> tonal values when you reduce exposure in editing. > > They're not really over-exposed, they have simply put your highlights on a > tone curve which makes the colors look pale. > > The whole point of you "exposing to the right" is to increase the signal- > to-noise ratio. The "number of tones" explanation often given is > incorrect. All digital cameras have too much noise at all tones to be > limited by numbers of tones, at least in the RAW data. The number of tones > in your output are unrelated to the number of tones in the RAW exposure; > you do not lose all you've gained when the software darkens the image. OK, the noise is more the reason but posterizing can be a problem in dark areas... raising shadows in post for the deepest shadows, and in skies where the color pallet is very limited. Doesn't the noise level follow this same principle? Or is there an unrelated reason for the noise levels paralleling tone counts? -- Paul Furman www.edgehill.net www.baynatives.com all google groups messages filtered due to spam
From: John Sheehy on 7 Oct 2009 16:44 Paul Furman <paul-@-edgehill.net> wrote in news:haibte$5o3$1(a)news.eternal- september.org: > OK, the noise is more the reason but posterizing can be a problem in > dark areas... The only cameras I know of with even a hint of RAW posterization are the Pentax K10D, which would profit from 13 bits instead of 12 at ISO 100 (not for 200 or higher), the Sony A900 also with a need for 13 bits at base, and the D3X when in 12-bit mode. These are only on the fringe of posterizing. > raising shadows in post for the deepest shadows, and in > skies where the color pallet is very limited. Doesn't the noise level > follow this same principle? Or is there an unrelated reason for the > noise levels paralleling tone counts? Any posterization you see in a RAW conversion is most likely caused by the math used in the converter, and nothing else. Of course, JPEG compression does some posterization of its own, especially if you use too much NR and it starts blocking up.
From: John Sheehy on 7 Oct 2009 18:19
"Charles" <charlesschuler(a)comcast.net> wrote in news:hagg86$ugf$1(a)news.eternal-september.org: >> Digital clipping is almost never "saturation of the >> sensor". Unless you are shooting at the base ISO >> clipping is saturation of the Analog-Digital-Converter >> (ADC) by sensor output that is greater than the maximum >> ADC input. > > And what difference would that make? There is no sharper knee than > one imposed by basic mathematics. 2^8 = 256, is a simple example. > With 8 bits, the maximum value is 255, base 10, with NO exceptions > possible. You actually help to make the case that over-exposed > digital shots guarantee lost information in the bright portions of the > scene. Exposure to the right is usually given as advice for RAW shooting. The RAW data usually clips well above the level where a JPEG would clip it, and the trailing color channels, usually red or blue, are less sensitive and blow out in the RAW data much higher than in a JPEG. For red, there is typically 2 stops more of highlight headroom in the red channel with daylight WB. For the blue channel, 3 stops with tungsten WB. Red is actuall being shot at double the ISO in daylight, and blue at 8x the ISO in incandescent light! > I continue to believe that exposing to the right is perpetuated by > folks with limited experience and knowledge. They are perhaps into > the dark parts of scenes and don't understand dynamic range. Many of > us are more greedy and want details at both ends of the luminosity > range. That depends on how and why ETTR is used. I don't see a whole lot of people recommending the act of blowing out the highlights to obtain ETTR. It is something you can do when you can; when you know it won't cause clipping. The advantage in SNR is tremendous. The shot noise, relative to signal, decreases when you increase absolute exposure (measured in absolute sensor exposure, ISO setting is irrelevant to shot noise except for potential clipping). The read noise decreases, relative to signal, too, especially when you are using Canon-style CMOS where the read noise comes mainly at a later stage in the signal chain, and are very close in intensity at all low ISOs (up to 400 or 800). With such cameras, you get a huge decrease in read noise (relative to signal) by using a higher ISO, if it doesn't cause clipping, without even increasing the absolute exposure. > Hey, blow those high-lites out! You're being ridiculous. You are completely dismissing the idea of ETTR, based on a reckless strawman. There is no connection between the idea of using ETTR when it is feasible, and using it haphazardly. > If that is the intended message of a > given scene, go for it. I don't care for over-exposed shots ... they > are just not my thing. I have seen some high-key shots that were > attractive and effective and do appreciate the skill and art of the > photographers who can pull that off. > > Specular high-lites might deserve to be blown out. Not the point of > my response. I'll just say it one more time and then go away ... if > it is clipped (by a sharp knee response curve ... due to sensor > saturation or A/D saturation or any saturation link in the chain) it > is GONE! If it is. It may not be, however, if you shoot RAW. For JPEGs, it is pretty trivial to set the camera up to produce low- contrast JPEGs, and then use darkening gamma correction to pull the tones back down to saturated colors. Low-contrast usually allows more of the RAW headroom to be used in the JPEG, and makes the highlight clipping indicator more accurate in most cases. The only time it not clipping when something is really clipped in the RAW, IME, is when the highlight is bright blue against a dark background, because a weighted RGB histogram gives very little weight to blue. |