I was recently shooting my new G80 in glaring midday sun conditions (shooting an event, couldn't choose the time of day) and was surprised to see what seemed like a bit too much noise at the base ISO, with so much available light. It was easily noticeable on people's faces, but only at 100% magnification, nothing really terrible. To calibrate "a bit too much" - this is in comparison to shots under more normal/diffused lighting (including shots from my em10ii). I suspect it had to do with some relative underexposure as the camera might have been fooled by the overall light available, and yet the faces were partially in the shade. But there was also quite a bit of noise in the blue sky. I see in LR that there was easily at least a stop of headroom available without blowing any highlights (in fact the whole scene as sun drenched). I was shooting in shutter priority and the camera chose the f-stop and therefore exposure, no exposure compensation dialled by me. Unfortunately I can't share the pictures, sorry. Anybody has similar experiences and thoughts on what could be causing this unintuitive outcome? Shall I always try to expose to the right? What is the best way to consistently achieve it without blowing the highlights? Anything else that I may be missing? Thank you.
The light that your camera gets is dictated by the exposure set, not how much light is available. 'Underexposure', contrary to what some say, doesn't cause noise because it's 'under' some 'correct' exposure, just because it's a smaller exposure. The rule is simple, the smaller the exposure the more the noise. To get less noise, use a bigger exposure. If you work to your exposure meter, then the way to get a bigger exposure is to use a lower ISO. I generally use my GX80 (which I guess is much the same as the G80) at 100 ISO, unless there are bright highlights, which can get clipped at the 'Lo' setting.
Also, sky noise os a particular thing, not to be confused with general noisiness. Firs, viewed in fine detail, the sky really is quite noisy,
due to uneven scattering (it is the scattering that gives the sky its blue colour) and specular reflections off water droplets and ice crystals in the atmosphere. If you have a camera without an AA filter, such as the G80, these tiny bright spots can alias and become more apparent rather than being smoothed out and invisible, as they should be. Then, a camera's sensor is at its least efficient in the blue part of the spectrum, so blue things will always look more noisy than other colours.
You posted a similar conjecture about "uneven scattering" due to ice crystals in the atmosphere five years ago, and it was pretty definitively addressed at the time by kenw
here. Has something changed since then to prompt you to once again submit it as a contributing factor?
Do you keep a database of my transgressions? That was five years ago, and I had forgotten all about that conversation.
No, I just have sufficient mental faculties to recall a thread in which I participated.
Glad to hear that you're not as obsessive as you appear.
Good. Now that we've established that I'm not as obsessive as I appear, shall we discuss whether you're as paranoid as you appear?
I wouldn't think it's paranoid to be amused by someone keeping tabs of you sufficiently to remember the details of a five year old discussion and further, to have a ready link to that discussion.
The very first sentence of your first reply to my first post here was a transparent effort to insult me by implying that I'm stalking you. And then you double and triple down with your follow-ups. Now, if you want to go down that path, I'm ok with it because I'm confident I can give as good as I get with the sarcastic jousting. What's not ok is when well after you, yourself, set the ground rules for what's acceptable dialogue, you then feign indignation over a single word ("preposterous") characterizing your conjecture. If you don't want others you interact with to respond with less than polite and neutral language suitable for publication in a scientific journal, then just don't start the conversation with a personal aspersion. Ok?
Now that we've got the ground rules for our future interaction ironed out, I'll demonstrate my good faith by withdrawing the use of the adjective "preposterous" when I refer to your sky texture conjecture. In its place I'll simply refer to it as "novel" because that's both neutral and accurate. Ok?
Like Ken, I don't think there's much more to be said about your novel conjecture until you provide at least some minimal controlled evidence, method for distinguishing it from ordinary image noise or at least one citation to a reputable source that directly describes it and offers a plausible explanation for the conditions that give rise to it. Continuing to reference any of the well known atmospheric phenomena we've already discussed, simply doesn't suffice unless and until you show how any of those phenomena can be present in clear blue skies that otherwise show none of the usual signatures for clouds, halos, sundogs, pillars, etc.
I await your response with real evidence and not just conjecture. Meanwhile, if you'd like we can discuss several of the other mistakes and mischaracterizations you've made. (See below.)
ii) You say these show 'typic;' sky noise. You ay what I said is 'preposterous'. What is your non-preposterous explanation?
Image noise. Plain and simple. In the case of blue sky, it's often the red channel that's polluted with noise. As I explained in my earlier post in the thread, the problem is triggered by a less than optimal exposure setting and then frequently made worse by adjustments that accentuate the problem (either in-camera or in post/processing). Subtle tonal ramps in blue sky can also lead to JPEG compression artifacts but that generally has a different more mottled look to it.
OK.
i) What do you mean by 'a less than optimal exposure setting'? My understanding is that as far as exposure goes bigger is better. I'm wondering whether you understand that there is some optimum other than bigness that we should be looking for.
Of course, if the only IQ criterion is noise, then a bigger exposure is always better. Of course, in the real world with real cameras being used by real photographers who don't understand all of the variables of metering, exposure and ISO as well as the impact of downstream processing/editing, it's often the case that they do not strike the optimal balance exposure and the other variables in play. You, of all people, should know that optimization of exposure is widely misunderstood.
ii) Please explain how JPEG compresses skies differently so as to leave artefacts in what should be a plain colour (JPEG is generally pretty good at that - it removes high frequencies, rather than adding them).
No, JPEG is not "pretty good" at removing high frequencies in subtle tonal ramps. It's actually pretty bad at it. Add noise to the equation and you not only get problems with banding but also a visible worsening of the noise into blotchy, mottled patches. Check out the images below. I create a synthetic 16-bit blue gradient in Photoshop and then added 1% gaussian noise to the left half of the gradient. See for yourself the impact of JPEG compession vs. the non-compressed PNG:
Converted to 8-bit PNG. No noticeable blotchiness and virtually no banding
[ATTACH alt="Converted to JPEG with "medium" compression setting in Photoshop. Note the blotchiness on the left where the noise was originally added, which is in addition to the visible banding across the image. Be sure to click on Show Original to view full sized."]1721338[/ATTACH]
Converted to JPEG with "medium" compression setting in Photoshop. Note the blotchiness on the left where the noise was originally added, which is in addition to the visible banding across the image. Be sure to click on Show Original to view full sized.
The JPEG rendering above clearly illustrates how even fine image noise can be enhanced into something rather ugly and easily characterized as "blue sky noise".
iii) Why do skies apparently behave differently from other plain colour areas? Or maybe you say that they don't.
So, I'd disagree that it was 'pretty definitively addressed'. In fact, coming back after five years, I think his case looks weaker than it did then.
You might like to look up the formation of light pillars, and you'll see that reflection off ice crystals certainly can cause visible effects in the sky. From the
Wikipedia article :
The crystals responsible for light pillars usually consist of flat, hexagonal plates, which tend to orient themselves more or less horizontally as they fall through the air. Each flake acts as a tiny mirror which reflects light sources which are directly above or below it, and the presence of flakes at a spread of altitudes causes the reflection to be elongated vertically into a column.
Easy to see how some random orientation of such crystals can cause random reflection in the sky, through to create a visible pillar, it need a particular orientation to the light source.
So what?
The so what is that there is a physically possible cause of the phenomenon I described.
We can also see rainbows. But rainbows and light pillars are relatively rare conditions.
Not the point. The point is that Ken claimed that my explanation was physically impossible because there aren't any particles in the air large enough to cause specular reflections. Yes there are. And we aren;'t talking about light pillars, we're talking about the ice crystals that cause ice pillars potentially causing other effects.
Again, you've provide zero explanation for how ice crystals many miles away are able to generate the specular reflections sufficiently large enough to look like well distributed and uniform noise but also very distinctly different from any well-known and well-explained naturally occurring atmospheric phenomenon.
This photo is taken from the Wikipedia article on halos
I don't think it's a stretch of the imagination to thing that the same phenomenon that causes clearly visible effects like this could, in a less ordered and more random alignment with the light, cause effects which are observable by a high resolution camera as being akin to noise.
This is a good example of where your effort at inductive reasoning falls apart. Nothing in this image looks like the uniform "texture" you claim can be present in clear blue sky. The reflections in this image clearly manifest themselves either as white, cloud-like or haze-like or distinctly patterned or distinctly colored. How you make the leap from well understood atmospheric phenomena like halos to evenly distributed blue sky "texture" IS the missing link. Your claim of "plausibility" in the absence of many, many years of scientific study of atmospheric optical phenomena would place the conjecture on one end of the "novelty" spectrum. However, considering that we do, in fact, have plenty of related science in the can and absolutely no mention of this particular phenomenon, your "plausibility" claim clearly falls at the other end of the "novelty" spectrum.
Blue "sky" noise is common and easily produced under all sorts of atmospheric and other conditions.
Sure. All sorts of atmospheric conditions have ice crystals in the higher levels of the atmosphere. It's cold up there.
Moreover, the claimed "randomness" of the reflection can't be correct because the light source of the specular reflections is the sun, which is always at some fixed position in the scene.
But the orientation of the ice crystals will be somewhat randomised. That's exactly waht is required. Have you ever seen 'glitter'?
The glitter, if distributed like ice crystals will have to be spread in a rather uniform/normal way across the sky, which at the scale we're talking about and with the randomized positioning of the surface of each piece of glitter, I would expect the effect to behave similarly to any of the number of well-described atmospheric optical effects (halos, sun dogs, glories, etc.) depending on the relative position of the sun. There will be specular outliers scattered around that stand out relative to their immediate neighborhood, but those will be isolated and not extremely uniform across the entire plane as is the case with blue sky noise.
That is your expectation, not mine. I would think that ice crystals in many situations could quite evenly be distributed around the atmosphere (see the 360 degree halo), and if the sun isn't in the right alignment for a visible halo, all you'll get is a random brightness variation at a very small scale from those crystals that are randomly in the correct alignment.
Again, I invite you to prove me wrong with even one reputable explanation of a known atmospheric optical condition that depends on specular reflection and that looks extraordinarily like regular image noise.
We're discussing possible cause., and as I said, if these ice crystals can provide structured, large scale visible phenomena with the sun in the right alignment, there is no reason to believe they won't provide more randomised, less structured effects with the light in other alignments.
Again, why hasn't this "plausible" phenomenon been widely discussed, described, measured, explained in the atmospheric science community...?
There's a reason why light "pillars" are pillars and not a uniformly random phenomenon across the sky (likewise with rainbows). Besides that, if it's a real visible phenomenon, then you'd expect ALL cameras under a wide range of exposure conditions to display it, but I've only ever seen complaints about it with respect to cameras that are relatively exposure constrained (e.g., high base ISO or otherwise insufficiently exposing the sky).
I don't know how many cameras suffer this effect and how many don't. I postulated that it's worse on ones without an AA filter, because sub-pixel bright spots will be aliased into larger effects. If that's the case, you'd expect some kind of dependency on the effect of the AA filter.
You're just guessing, here, but for whatever it's worth my mFT cameras and my D300 all have AA filters and all produce blue sky noise under the right conditions.
Sure, it's a speculation. But, I'm not inclined to take your observations as a data point, since it's very clear that your mind is closed on this matter.
My mind is not "closed." It's open to evidence. You've offered none.
It's also not immediately clear that we're talking about the same phenomenon. In any case, as I remember at the time the D300 had a bad reputation for 'sky noise' compared with the D200.
The obvious difference is that the D300 was configured with ISO 200 being its nominal base ISO, whereas the D200 was configured with ISO 100 being its nominal base ISO. Accordingly, D300 users would tend to more frequently (if unnecessarily) shoot blue sky scenes at ISO 200 than at the "low" setting that would match the D200's nominal base ISO of 100.
Your position seems to be that the 'sky noise' phenomenon, doesn't exist as anything different from normal noise. You may be right, but it seems to be quite often observed, so finding an explanation seems sensible, even if that explanation is that the people who observe it are delusional.
I was one of those "delusional" D300 photographers. Your efforts and the efforts of others to educate me about what's really going on taught me how to effectively deal with the issue on my base ISO bound cameras like the D300 and, now, my mFT cameras.
The theory simply doesn't hold up.
I still think it does. Your refutals certainly don't hold up, because they simply don't address the point being made.
What point?
Any point.
Blue sky noise is always uniformly distributed and changes in amplitude consistent with the amount of light captured by the sensor.
Is that the case? I'm not saying that you're wrong, but I've never, ever seen a rigorous evaluation showing this. Presumably, such a stickler for well founded arguments such as you wouldn't be making such a claim unless it had been rigorously verified, so let's see the source.
The source is my years of personal experience using high base ISO cameras that are prone to generating visible blue sky (and water) image noise. Since I tend to exposure-bracket to ensure optimized raw exposure and to extend my image DR through stacking, I end up with a lot of "underexposed" (for raw) frames that are comparable to the exposures other users frequently obtain when using conventional metering. With years of experience viewing these different exposures of the same scene, it's abundantly obvious to me that the variable that differentiates the frames in which sky noise is visible from those in which it isn't is simply exposure. I've literally done this "test" hundreds of times over the years.
OK. So, your position is essentially that 'sky noise', as a separate phenomenon, does not exist. Possibly that's the question to get out of the way before possible causes are discussed. If your starting point is that a phenomenon doesn't exist, then you'll reject absolutely any explanation as to what causes it.
That's a mischaracterization. My rejection of your conjecture isn't "absolute." I am open to evidence and support, but you haven't offered any.
It looks like typical image noise and behaves like typical image noise because it it IS typical image noise.
So, no , why is the sky particularly subject to ';typical image noise'; when other flat areas, even blue ones, aren't?
But they ARE, given the right set of lighting, metering and processing conditions. What particularly distinguishes image noise in the sky (which is usually blue, of course) from similar amounts of noise in other areas of an image with a similar EV is that we
know a priori that the sky should be uniform and textureless. Sky noise sticks out like a sore thumb but noise in other lower midtonal areas of images tends to get hidden by real detail. It's relatively rare to come across those other "flat areas" that aren't in the sky.
So, purely an expectation effect? That merits discussion.
Then, please, let's discuss. Bear in mind that I bring considerable personal experience and personal interest and study of the issue to the discussion precisely because I've extensively used the cameras that are often accused of generating blue sky noise and precisely because I've closely monitored the discussions and claimed examples over the years. The outcome of the issue has had and will continue to have a very direct and personal effect on my photographic interests.
, spectaculair to watch and sometimes they forget to stop before they reach the ground.
