Seeing any Posterization issues with A7r ll?

[Vivek]

Guy, Why invoke science and engineering, there are many good ones that are also capabale just as there are good photographers who can read light and make their tools capture it.

 

[Guy Mancuso]

Well because I know for a fact at those elevations the wave length changes. That's my brain knowing that but I need engineers to do the match and science on how much it would effect the file. That part is where I get off the bus and ask for directions. We need the science but we also need the reality

 

[jlm]

quite a few factors contribute to the relative IR-UV content at different elevations and it's effect, atmosphere and atmospheric composition being one. also angle of light, reflectivity of surroundings. e.g.: air in tokoyo vs Chamonix; snow and sand, dark earth, high noon, vs sunset, spectral sensitivity of the sensor, film (or your skin, for example)

when skiing or at the beach, you need dark UV safe eyewear and sunscreen; if photographing near snow, definitely a UV filter, etc

 

[Iliah Borg]

so that might mean that the relative proportions of red to blue light were low? Not sure if Lloyd's polariser was also a uv?

Blue channel on non-UV-enabled silicon sensors has extremely low sensitivity to wavelengths shorter than about 380nm, UV per se should not be an issue, sensors are not like film in that regards. Page 6 of http://www.lpriami.altervista.org/I...or_Response_Curve_Comparison_for_ICX445-4.pdf gives an idea. Also, most of the lenses attenuate UV dramatically.

But red to blue ratio on the water and in skies is always low, which makes the red very important, but very brittle at the same time (it is red that adds all the drama in the sky, bw photographers know it allright). That ratio can be easily worse with a polarizer. With digital cameras, red and magenta filters are still useful to remedy this problem.

 

[Guy Mancuso]

So no one has a answer to my question.

 

[timparkin]

So no one has a answer to my question.

Yes you are right. This is due to molecules scattering higher frequencies of light from the sun (Rayleigh or Tyndall Scattering). However this blue light has to travel through the atmosphere to get to your eye and hence it gets attenuated itself (the blue light trying to get to your sky get attenuated by scattering). Add in dust scatter and humidity reduced viewing distance (haze) and the lower you are the more non-blue light reaches you as well.

High up you get a deep blue because less blue is scattered but there is less (also thinner) atmosphere to pollute the blue.

Add a polariser to this and you can end up with the sky almost black (you effectively have a luminance control of the blue channel with your polariser).

Reflections from waves will alternately reflect the black, polarised sky and possible areas of non-polarised sky (and maybe transparent areas showing the green of the water).

Tim

p.s. Dana Lake is at 11,100 ft

 

[Guy Mancuso]

Thanks Tim appreciate this so should we be adding this to the effect that he is getting. The problem to this file is it really started off bad or everything against it to begin with than obviously post and other issues it went to hell in a hand basket.

Really if you ask me a lot on contributing factors and not necessary pointing in one area but basically a combined fail.

I know when I shoot up there we use IR ND filters

 

[Vivek]

Really if you ask me a lot on contributing factors and not necessary pointing in one area but basically a combined fail.

I would think not.

Metamerism failure is directly equated to lossy RAW files (the original query in this post). I think that is wrong.

The sidebar/discussions are all fine and very enlightening but the reviewer came to the wrong conclusions not recognizing what he did wrong.

 

[tashley]

I would think not.

Metamerism failure is directly equated to lossy RAW files (the original query in this post). I think that is wrong.

The sidebar/discussions are all fine and very enlightening but the reviewer came to the wrong conclusions not recognizing what he did wrong.

So just to be clear Vivek, what did he do wrong in your view?

 

[Vivek]

So just to be clear Vivek, what did he do wrong in your view?

Making a story that the lossy RAW was to blame for his posterization snaps.

 

[tashley]

Making a story that the lossy RAW was to blame for his posterization snaps.

So are you 100% certain that the posterisation has nothing to do with lossy RAW?

If so, what have you concluded was responsible?

 

[Vivek]

Perhaps you read selectively, Tim?

I said metamerism failure (here or another thread). Guy has brought in his pesronal experience to that as well.

 

[tashley]

Perhaps you read selectively, Tim?

I said metamerism failure (here or another thread). Guy has brought in his pesronal experience to that as well.

I have a reading age of 54. I asked what Lloyd did wrong, and you replied:

"making a story that the lossy raw was to blame for his posterisation snaps"

I think it's reasonable, given exactly what you wrote, to ask what therefore WAS in your view responsible. No?

 

[Vivek]

I have a reading age of 54. I asked what Lloyd did wrong, and you replied:

"making a story that the lossy raw was to blame for his posterisation snaps"

I think it's reasonable, given exactly what you wrote, to ask what therefore WAS in your view responsible. No?

Hi Tim, when the answer has been provided and if keep repeating your query, there are several possibilities (reading age being not one, i would think since I am in the same age bracket, well over the hill anyway)- a) I am not clear (can't do much about that), b) you do not understand what is said c) you do understand but refuse to accept what i said.

Cheers! :chug:

 

[tashley]

Hi Tim, when the answer has been provided and if keep repeating your query, there are several possibilities (reading age being not one, i would think since I am in the same age bracket, well over the hill anyway)- a) I am not clear (can't do much about that), b) you do not understand what is said c) you do understand but refuse to accept what i said.

Cheers! :chug:

a)

 

[waardij]

It is somewhat surprising that Lloyd does apparently not have to explain himself. a lot of things he does not like are blamed on 'cooked' RAW files, which apparently means the compression algorithm. And as far as I know without really understanding the basic thinking behind the compression. the part of the compression where Sony divides an image up in squares and limits the dyncamic range within that square to less then the full dynamic range of the sensor, is certainly a potential problem. there are plenty of examples of how this mechanism can cause visible artifacts (although I have never encountered it in a file of mine, and apparently this goes for a lot of other Sony users as well). the other part of the compression, the part that apparently is blamed for posterisation and maybe even for 'orange peel', is not really lossy in the sense that little or no information is being lost. this is the part is where the tone curve is being compressed. so this part of the compression would influence parts of the image with little detail and low contrast (like in the example where posterisation occurs). there is less resolution after this operation, but the reasoning behind it is sound in that the part of the resolution that is thrown away does not contain information, but only (mostly) shot noise. It is possible to have a philosophical discussion about what is lost or not, and whether this could degrade an image, but this is unlikely to have much practical value. and Lloyd would not be an interesting partner in such a discussion, since he does not seems to be willing to try and understand the underlying theory (he and I have had discussions about this in the past).

 

[mjm6]

Perhaps you read selectively, Tim?

I said metamerism failure (here or another thread). Guy has brought in his pesronal experience to that as well.

Vivek,

I'm not sure you are using the term metamerism correctly in this context? I don't believe this is an issue of the colors appearing differently under two different light sources.

I do agree that Lloyd appears to have made more of a fool of himself than add anything to the web knowledge base on the new camera or enlighten the masses on any issues of RAW compression.

I don't know if the Sony a900 uses the exact same compression algorithm, but if it does, it would be possible to construct an A/B comparison to see if the RAW compression added to the problem that he experienced. I suspect that any impact is minimal at best, and it is almost entirely a case of gamut and spectral sensitivity in combination with the polarizer and elevation.

That said, since RAW compression is obviously the boogieman, Sony could eliminate it as the problem de jure with some effort, and eliminate most of these inane discussions.


---Michael

 

[Iliah Borg]

Yes you are right. This is due to molecules scattering higher frequencies of light from the sun (Rayleigh or Tyndall Scattering). However this blue light has to travel through the atmosphere to get to your eye and hence it gets attenuated itself (the blue light trying to get to your sky get attenuated by scattering). Add in dust scatter and humidity reduced viewing distance (haze) and the lower you are the more non-blue light reaches you as well.

High up you get a deep blue because less blue is scattered but there is less (also thinner) atmosphere to pollute the blue.

Add a polariser to this and you can end up with the sky almost black (you effectively have a luminance control of the blue channel with your polariser).

Reflections from waves will alternately reflect the black, polarised sky and possible areas of non-polarised sky (and maybe transparent areas showing the green of the water).

Tim

p.s. Dana Lake is at 11,100 ft

Dear Tim,

To put some numbers to this,
{"Sony", "ILCE-7RM2", "Daylight", {2.42578f, 1.0f, 1.58203f, 1.0f}},
{"Sony", "ILCE-7RM2", "8500K", {3.06250f, 1.0f, 1.23438f, 1.0f}},

The above is white balance multipliers for R, G1, B, G2 channels.
R to R ratio is 3.06250 / 2.42578, that is at 8500K CCT the response in red is 80% of what it is for the normal photographic daylight, 5500K. This alone is too small of a difference to have a drastic effect - it is 1/3 EV only.

But a polarizer complicates the situation by an unknown factor, as we do not know neither the primary effect - the angle (polarizer rotation), nor the secondary, that is how the polarizer (again, at the given angle) interferes with polarization effects in the sensor sandwich.

 

[Iliah Borg]

> add anything to the web knowledge base
Lloyd presented experimental data and demonstrated several important issues:
- imperfection of default colour management;
- importance of watching for per channel exposure;
- importance of watching for extreme attenuation of the red channel due to the use of polarizing filters (falls somewhat into the per channel exposure);
- complete voids in raw data coming from the camera, stretched to 7-8 missing values after applying white balance (posterization of raw data).

I would say it is quite a lot.

 

[jrp]

I suppose that the question is "which of these effects are features of this camera and which would happen with competing models"? In particular, which are attributable to the compression algorithm that Sony have chosen to adopt.

The idea that removing the compression is just a matter of tweaking the firmware may or may not be the case. Sony's reluctance to offer the option of losslessly compressed raw suggests that there would be unwanted side effects. It would be interesting to know what those would be. Since it is reasonable to assume that the Sony engineers are not idiots, they have chosen the processing pipeline for a reason. I am not clear what it is? Card space saving? Frame rate? ... ? Does anyone else?

I have read that Sony / Minolta used to have a non-lossy compression, provided the option of this lossy one, and moved over to it completely, when no one complained.

The idea that ree to offer the option of losslessly compressed raw suggests that there would be unwanted side effects. It would be interesting to know what those would be.