"Exposing to the right" is over exposed, what now?
in [Photoshop]
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From: Floyd L. Davidson on 8 Oct 2009 06:06 Paul Furman <paul-@-edgehill.net> wrote: >Floyd L. Davidson wrote: >> That is exactly the point I *am* making. WB changes >> the >> histogram in a useful way. The Luminous-Landscape >> article did not talk about WB at all. They discussed >> changing the camera's setting for contrast, and that >> simply does *nothing* useful for the histogram/exposure >> issue. >> And if you doubt that the contrast setting will not >> change >> the histogram as stated, *try* *it*. I gave an step by >> step description of a very easy way to show exactly what >> does and does not happen. Why argue from supposition when >> you could actually learn something about photography... > >I am interested in learning. I tried fiddling with the camera contrast >settings to compare histograms and the difference was very minor, at >least for the conditions I tried just now. I was thinking of >post-processing where increasing contrast blows highlights & blocks >shadows. Maybe not the very final edge of 100% saturation but contrast >adjustments can make a big difference in what appears to be blown or >blocked. What you are describing sounds more like a gamma adjustment >than contrast where only the middle part shifts. "Gamma is equivalent to contrast. This can be observed in traditional film curves, which are displayed on logarithmic scales (typically, density (log10(absorbed light) vs. log10(exposure)). Gamma is the average slope of this curve (excluding the "toe" and "shoulder" regions near the ends of the curve), i.e., the contrast." http://www.imatest.com/docs/glossary.html (The above is a web page owned by Norman Koren.) "Gamma -- A way of representing the contrast of an image, shown as the slope of a curve showing tones from white to black." http://www.hp.com/united-states/consumer/digital_photography/articles/scanner_glossary.html That might help make things clearer as to why changing contrast does not make the histogram any more or less accurate for exposure. When the histogram indicates precisely the correct exposure, changing the gamma (contrast) moves the curve between black and maximum white values, but it doesn't change the value of either. Note too that it might spread the histogram out from the center (if the gamma curve is moved by picking a point at its center), or it might move towards ether the right or the left (if the gamma curve is moved from point closer to the ends instead of at the center). In any case, it changes the contrast but if there are image values at the maximum white value they will not be moved. >An interesting related issue I don't understand is how the exposure >slider works in Lightroom or ACR. I don't know how to duplicate that >effect in photoshop with curves, levels, etc. Those all do like you >describe, moving the middle parts of the histogram but there isn't an >easy way I can see to shift the whole exposure. Hmm, the middle slider >on levels comes close but still doesn't match the effect. I don't use those programs so I can only provide general instructions about how that is typically done. I'll leave it to someone who can be more specific. -- Floyd L. Davidson <http://www.apaflo.com/floyd_davidson> Ukpeagvik (Barrow, Alaska) floyd(a)apaflo.com
From: Floyd L. Davidson on 8 Oct 2009 06:22 Paul Furman <paul-@-edgehill.net> wrote: >John Sheehy wrote: >> Paul Furman wrote: >> >>> 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. > >OK, this makes sense, the posterizing issue is not really visible in any >sort of normal exposure. What about Floyd's comment below that the noise >level remains the same but exposing to the right increases the signal so >that overwhelms the noise? That seems to tie the two together in a >comprehensible way. The LL link just makes a lot of sense, it can't be >complete BS. http://www.luminous-landscape.com/tutorials/expose-right.shtml That is an *excellent* article. It also has a link to another article, titled "Understanding Histograms", which several contributors to this thread could benefit from (particularly the histogram of the moon shot and the high key tree image that are the last two shown at the bottom of the article): http://www.luminous-landscape.com/tutorials/understanding-series/understanding-histograms.shtml -- Floyd L. Davidson <http://www.apaflo.com/floyd_davidson> Ukpeagvik (Barrow, Alaska) floyd(a)apaflo.com
From: DRS on 8 Oct 2009 08:33 "Floyd L. Davidson" <floyd(a)apaflo.com> wrote in message news:87ab02ql1h.fld(a)apaflo.com > "DRS" <drs(a)removethis.ihug.com.au> wrote: [...] >> I have always said it changes the indication of exposure. It is you >> who made the false claim that I and others were saying it had >> anything to do with changing the actual exposure, which we have >> repeatedly denied. > > *All* *five* *show* *the* *exact* *same* *exposure*. Yes, how many times do I have to tell you that before you get it? > Not one of them shows any 1 f/stop difference as you > claim. Yes, they do, in terms of *accuracy*. > The only thing that moves 1 f/stop are the tall peaks in > the graph that have *nothing* to do with exposure. It > is well to the left of the right edge, and it is that > right edge that indicates exposure. The right edge moves. >> And because of the different contrast settings the 5 histograms show >> the exposure differently. The exposure hasn't changed but the >> accuracy of its representation has. Which is all that has been >> claimed. > > They *don't* show the *exposure* differently. Yes, they do. Everybody can see it except you. >> None of the 5 histograms indicate overexposure. What they do >> indicate, to different degrees of accuracy, is the room for exposure >> compensation. Only 1 can be the most accurate and it is the -4 >> histogram. > > All of them indicate there is no room for any > "compensation". Increasing the camera exposure will > result in clipping, and each of those histograms shows > that. No, they don't. Try looking at what is there. [...] >> In this instance that indicates specular highlights, which as has >> been noted by several people, may be blown without spoiling the >> image. That is a choice by the photographer. > > The tall peaks are *not* a "specular highlights", and I didn't say they were. Do you ever pay attention? You can't even follow when I'm addressing your argument! [...] > You know, logically if what you said made sense the > article would have discussed it in some way, but it does > not even hint at it. If changing the contrast displayed > a more accurate *exposure* (right edge location), why > didn't they point to it? "What does all this mean? In order to display the full dynamic range of your camera in the histogram displayed on the back, you must set the contrast to minimum. You now can see the same dynamic range in the histogram on the camera as you will see it in your RAW processor on your computer."
From: Porte Rouge on 8 Oct 2009 09:35 On Oct 8, 6:22 am, fl...(a)apaflo.com (Floyd L. Davidson) wrote: > Paul Furman <pa...@-edgehill.net> wrote: > >John Sheehy wrote: > >> Paul Furman wrote: > > >>> 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. > > >OK, this makes sense, the posterizing issue is not really visible in any > >sort of normal exposure. What about Floyd's comment below that the noise > >level remains the same but exposing to the right increases the signal so > >that overwhelms the noise? That seems to tie the two together in a > >comprehensible way. The LL link just makes a lot of sense, it can't be > >complete BS.http://www.luminous-landscape.com/tutorials/expose-right.shtml > > That is an *excellent* article. It also has a link to > another article, titled "Understanding Histograms", > which several contributors to this thread could benefit > from (particularly the histogram of the moon shot and > the high key tree image that are the last two shown at > the bottom of the article): > > http://www.luminous-landscape.com/tutorials/understanding-series/unde.... > > -- > Floyd L. Davidson <http://www.apaflo.com/floyd_davidson> > Ukpeagvik (Barrow, Alaska) fl...(a)apaflo.com Hey, that's the same article you said this about: "But regardless of that, the cited URL above from luminous-landscape is *not* full of good stuff. They miss the point entirely, and provide nothing that is actually useful!"
From: Porte Rouge on 8 Oct 2009 09:40
On Oct 7, 8:21 pm, "Wilba" <use...(a)CUTTHISimago.com.au> 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. > > Yes, reducing the exposure in Lightroom just puts your histogram back to the > left, so that's a waste of time. To avoid having the deep colours washed > out, you need to make use of the full tonal range available in the image. If > you have done a good job of exposing to the right, your highlights will be > pretty much where they need to be. So then all you need to do is raise the > black point (e.g. using the Levels dialog in Photoshop), so that the dark > tones in the scene end up as dark tones in the image. If you are using the > Levels dialog in Photoshop, while you drag the black (or white) point > slider, press the Alt key to see which pixels are clipped (or blown). > > (The following relates to my experience with a Canon 450D. YMMV.) Aha! > > There are two parts to exposing to the right - levels in the image and > saturation of photosites. Whether you are shooting JPEG or raw, the camera's > histogram display shows you the levels in a JPEG produced from the raw data, > so the shape of the histogram curve depends on your settings for sharpness, > contrast, saturation, colour tone, etc. > > If you are shooting JPEG, all you can do is avoid piling up the histogram on > the right, which prevents gross areas of blown highlights in the image. > > If you are shooting raw, you can overexpose (beyond the point at which the > histogram curve touches the right boundary), by about two steps and still > produce an image from the raw without blown highlights. IOW, the headroom > between blown highlights in the JPEG and saturation of the photosites is > about two steps (in my experience, with the JPEG settings I use). > > So if you are bracketing for the best possible exposure, go at least two > steps over what the histogram tells you is "correct". The maximum possible > dynamic range occurs at the point where photosites in the highlights begin > to saturate. > What do you mean by steps? Do you mean stops, or steps on the aperture or shutter dials? > In everyday raw shooting, you can be quite relaxed about having a small > spike on the right of the histogram - that's actually a good thing. |