November 21, 2014, 05:57:54 AM

Show Posts

This section allows you to view all posts made by this member. Note that you can only see posts made in areas you currently have access to.


Messages - jrista

Pages: 1 2 [3] 4 5 ... 309
31
EOS Bodies / Re: Canon 7Dii vs Nikon D750 Dynamic Range Test
« on: November 13, 2014, 08:48:04 PM »
I checked Sensorgen.info on the D750. According to those numbers, the maximum DR is 13.9...so slightly over capacity for the T4110, but close enough that I think it's workable.


I also calculated the gain for ISO 100. Assuming 2^14 - 600 is the maximum numeric value, that means the gain is 81608/15784 e-/DN, or 5.17e-/DN. The read noise at ISO 100 is 5.5e-, so 5.5/5.17 = 1.064 DN. In terms of minimum read noise in a D750 NEF, the STDev can, theoretically, get as low as 1.064. I don't know what temperature DXO tests at, however temperature does play a role, as dark current noise doubles every ~5.8°C, and with read noise levels this low, even with CDS, a change in temperature can change that 1.064 to 1.1 or 1.2 or more pretty easily.


Without accounting for temperature and dark current, the dynamic range that we are likely to measure in tests with a Stouffer wedge could very, very easily drop below the 13.9 stops as measured by DXO. So I still think that the 13.7 stops available in the wedge is good enough to measure the DR of the D750.

32
EOS Bodies / Re: Canon 7Dii vs Nikon D750 Dynamic Range Test
« on: November 13, 2014, 08:31:18 PM »
My last post directed at Domino Dude. Not you Jrista.  8)


Right, but...he was correct. ;P And I was also responding to what you were saying about needing 14.5 stops. You don't, your current wedge has plenty of space to handle what were saying you should try doing to make proper use of the wedge and get accurate dynamic range readings.


Oh, another thing. The 14.5 stops...I haven't checked, but I assume that is what DXO is reporting as the D750's dynamic range? That is incorrect. That is the NORMALIZED dynamic range. The "Print DR" as they call it. You should be referencing their Screen DR numbers instead, since your images are 100% full size. You are not downsampling them (and neither have I been in my analyses in PI), so Screen DR is the only number reported by DXO that is going to accurately represent the "hardware DR", or the DR of a non-scaled RAW image. I am trying to check DXO now, but their site is mind-bogglingly slow, and isn't loading the page. I assume that the Screen DR is less than 14.0...as mathematically it is impossible to have more than 14 stops of DR with 14-bit data. I suspect it is somewhere between 13.5 and 13.8 stops Screen DR, in which case, your wedge has just about enough space to accurately measure the dynamic range of the D750.

33
Animal Kingdom / Re: Show your Bird Portraits
« on: November 13, 2014, 08:30:45 PM »
@Jack: Sweet setup! I love it! I think your perspectives are definitely better. Must be nice to be at bird level, eh? ;)


One thing I would recommend, is loosen up your framing a bit. Your shots tend to be extremely tight, and I think they could be positively impacted by a bit looser framing, with some negative space around the birds.


Anyway, great shots. Looking forward to seeing what kind of photos you get now.

34
EOS Bodies / Re: Canon 7Dii vs Nikon D750 Dynamic Range Test
« on: November 13, 2014, 08:24:10 PM »
Looks like we will disagree on this. It is kinda hard to measure supposedly 14.5 stops of DR on a 13.7 strip, with really 13.3 EV to work with. The way I see it, the slider does allow us to recalibrate the analysis, clipping the first point off starting from 2 stops in, Id love to understand why that is an unreasonable assumption. Add that two stops back in after the calculation and both cameras are well within the ballpark of much more expensive methods.

Again, if you have a better suggestion I am all ears.


It is not a disagreement, Michael. I don't mean to be rude, so with all due respect, you are misunderstanding how to use the strip. You don't need 14.5 stops, because you are not even making full use of the 13.7 stops the strip you have now currently offers. Until you clip swatch 1, you are under-utilizing the Souffer 4110 Wedge. It isn't a matter of opinion here, it is a matter of proper application. It is necessary to clip that first stop. The rest is a simple matter of mathematics.


I checked out the statistics in PI, calibrated to 14-bit. In 14-bit number space, the Max (Swatch 1) and STDev (Swatch 36/40) values are:


5D III (Red): 12282/10.5
D750 (Red): 13644/2.5


5D III (Green): 11300/5.8
D750 (Green): 12144/1.3


5D III (Blue): 12923/7.5
D750 (Blue): 12941/1.5


In terms of dynamic range, the formula when using digital numbers is 10 * log(Max/Stdev) * 3 (similar but slightly different to the formula when using electron charge) , which takes the maximum (saturation) over the standard deviation of noise (of a swatch where SNR reaches a ratio of ~1:1...I used the first swatch where the seam between it and the next swatch was not visible in each image, as every swatch after that looked the same (for some reason the PI statistics window doesn't actually directly report SNR, so this was my only real option)...this was swatch 36 for the 5D III, swatch 40 for the D750). I ran the above formula, and got the following:


5D III (Red): 10.22 stops
D750 (Red): 12.45 stops


5D III (Green): 10.96 stops
D750 (Green): 13.23 stops


5D III (Blue): 10.78 stops
D750 (Blue): 13.12 stops


The red channel in the D750 image is exposed a little bit more than the other two channels, and that seems to weight the noise, hence the reason that channel has 12.45 stops instead of 13.something. These numbers seem to be pretty in line with what I was expecting, given the exposure level of swatch 1 in both images.


To actually reach 13.7 stops of dynamic range, we need the maximum level to be 2^14 - offset. In a Canon camera, the bias offset is 2048. In a Nikon camera, the clipping offset is 600 (this is based on work by some guys at Nikon Hacker who figured out how to restore a bias offset to Nikon cameras for astrophotography purposes, which after the black point clipping was removed, resulted in a bias offset of 600). So, for the 5D III, the maximum level that can be reached in a given pixel is 14366. For the D750, it is 15784. At those levels, to reach 13.7 stops of DR, you would have to have read noise as low as 1.113 for the 5D III (not going to happen), and 1.23 for the D750 (well, it got as low as 1.3 in the green channel...so, maybe.)


Anyway, if we run the math with those numbers:


5D III (Max Stouffer DR): 10 * log(14366/1.11) * 3 =  13.7067 stops
D750 (Max Stouffer DR): 10 * log(15784/1.23) * 3 = 13.69437 stops


With maximum saturation numbers like 12282 and 13644, you are exposing WELL below the clipping point on swatch 1. Swatch 1 needs to be clipped, then swatch 2 would be used as the maximum saturation swatch, and whichever the first swatch where the seam between it and the next becomes invisible would be used for the standard deviation (SNR 1:1) swatch (this, at least, is the only way it could be done using PI statistics...I am honestly not sure which swatch is truly where SNR 1:1 would first occur...but I don't have any better way at the moment given the tools at my disposal, and once all the dark swatches reach a point where they all look the same and blend into each other, you HAVE reached the minimum usable level.). That is the only way to properly use the Stouffer T4110 Step Wedge. Otherwise you are under-utilizing it.


Based on the numbers above, your about two thirds of a stop or so under-exposed, which is fairly significant.

35
Cool..  another mega scope.

With the European ELT at 39m and this one at 30m, all the ~8m class ones are going to look a bit outdated.

Those two are going to be wonders of the world.


Yeah, I was just researching these not two weeks ago. Amazing feats of engineering...the designs for everything, not just the scopes but the entire infrastructure to support them as well, are just phenomenal. The ELT in particular, I think that one is pretty much at the limits of our current engineering capabilities. They will be able to resolve more resolution than Hubble, and below the seeing limit, thanks to the advanced active optics technology...which is mind blowing.

36
EOS Bodies / Re: Canon 7Dii vs Nikon D750 Dynamic Range Test
« on: November 13, 2014, 05:44:44 PM »
When you say "get a good reading"...with what?

For example, if I clip out on the D750 in RAW, the swatch itself only has another 13.3 stops left to analyze. If a cameras DR is 14 or more, we wouldn't be able to see it because of the limit of the strip.


That's ok. I understand the limitations of the Souffer strip. What I am saying is, if you do not...overexpose, swatch 1, then your not actually able to measure the true DR of the camera. Tight now, swatch one is being exposed about 21% or more below the point where it "clips out" (see below...I think there is just a misunderstanding of this term). If the D750 has, what, 13.8 stops, then at best, if we got the necessary statistics (which I think we have, I'll have to see about actually calculating the DR for real), then I would say at best, the data would show only around 11 stops for the D750, and maybe 9 stops at best, if that, for the 5D III. Because the highlight levels stop 21% below the digital clipping point...levels 201 through 255 are not being used...so your effectively throwing them away in your test.


Does that make sense? I can try to think of a better way of explaining...

When you suggest clipping out that first swatch, what that means is there won't be enough room on the remaining part of it. They don't make a strip with anything more. Ill think about this. 4 stop ND filter in front of a portion of it perhaps?


No, I think your just misunderstanding, and that is probably my fault for not explaining properly. I don't mean actually, say with scissors, "clip" off any part of the chart. :P I mean, expose it enough that the digital values "clip"...in this context, the word clip means that you have exposed enough that the highlight values in swatch one need to be say 257, 258, 260...but the numeric space only allows you to go up to 255. When you need numbers that are outside of the available numeric space, the technical term for what happens to them, they end up being the maximum allowed value of 255 instead of 257, 258, 260, is that those values are "clipped". It's a virtual thing, a numbers and math thing, not a physical thing. :P


I will see if I can demonstrate better when I get home. Basically, right now, your not using all of the strip. I'm trying to say, there is more room (digitally, in terms of number space, not anything physical) on the strip than you are using so far, because your not 'clipping' (or ever so slightly over-exposing) swatch 1. I don't mean you have to clip it heavily...you just need to get the levels in that swatch to say between 253-255 (and some will probably be brighter than that, hence why they are "clipped"). Once you get to that point, then you will fully be utilizing the entire strip properly.

37
EOS Bodies / Re: Canon 7Dii vs Nikon D750 Dynamic Range Test
« on: November 13, 2014, 05:23:17 PM »
Jrista- hey I wanted to thank you for taking the time to put that all together, I really appreciate it. Your comments and several others have really helped me with presenting this information in a much cleaner way.


You are very welcome.

I have taken many different exposures (bracketed) and what happens is when clip out in the RAW file as it is opened, I don't have enough swatches on the strip to get a good reading.

Additionally, even at the same exposure settings and flash power, some cameras still exposure slightly differently, I see it all the time in side by side shooting.


When you say "get a good reading"...with what?

I am very curious about the software you mention, is anything you are aware of that can measure the signal to noise ratio of a specific swatch? Maybe cropped? I have some ideas, but it would be easier to measure a specific swatch.


I was measuring on specific swatches. What I did in PixInsight is draw previews around the center part of individual swatches. In the Statistics tool, I can select any one of those previews, and get SNR and other details just for that one swatch. It's very useful.


Im still curious if it would be reasonable to add the total Exposure Slider value (in this case 2.0) if my me more serves me correctly, to the swatch reading (lets say 32-33, would be 10.67EV, or 12.67 ev, minus the one over exposed swatch, for a total of 12.33EV.? If we could precisely measure the signal to noise ratio threshold on both swatches instead of eyeballing it, it could very well be a cheap and easy way to at least estimate the ball park DR.


I would need to know more about how your getting the DR readings. Adding exposure is not the right way...that is a modification after the fact, so you are not getting a valid DR reading of the camera. You really do need to expose Swatch #1 up to the point of clipping (maybe not fully clipped, but just to the point where it begins to clip). Otherwise, you are throwing away dynamic range, and more darker swatches will be buried in the read noise.


If your underexposing swatch 1...and, based on my analysis, your currently underexposing it A LOT, I mean, a LOT LOT, way too much since the levels are ~200 in 8-bit, which means you are throwing away ~55 levels, or over 21% of the signal space. Your throwing away DR. Or in other words, you are not actually measuring the full dynamic range of the sensor.



The key here is to expose as close to the limit as possible, so that fewer dark swatches become "dominated by noise", or close to that 1:1 SNR, where it doesn't really matter how much NR you do (and, I spent a lot of time trying to figure out a way of recovering the noise-ridden swatches from the 5D III image, the ones where you couldn't see the seam between swatches...there simply isn't any way as far as I can tell...nothing in PixInsight and none of my NR tools in PS, including Topaz and Nik...could recover anything useful below, what was it, swatch 35?)


I don't think that is going to change the results. Not much. The 5D III may gain one swatch on the D750...but the D750, which already demonstrates great performance right down to swatch 41, is going to get better as well once you push swatch 1 to clipping.

38


This place would be FAR more peaceful if you would just leave people alone. Regardless of how wrong they may be.

Seriously, how can you say that with a straight face, are you bipolar?

We, neuro, you, and I, and a few others, are all pots and kettles, for one to call the other out as black is farcical.


And I think we all need to back the hell off of people, and stop antagonism. I've tried, I generally try to avoid you guys these days, but if you guys aren't pounding on me, your pounding on someone else. I'm backing off now. Let's see if any of the rest of our little group can just leave well enough alone and let this place be in peace, or not.

39
Do you enjoy emberrasing and belittling and degrading people? Honestly, dude.

Ooooo looky, maybe I'll now be awarded another yellow box for pissing off jrista.  Did someone appoint you Defender of Trolls while I wasn't looking?   

Maybe the moderator cleanup was fast enough that you missed Jon_D's little tantrum of posting a three-word inanity in a whole bunch of threads that had been inactive for ~4 years.  I suppose that since the mods deleted it, you also missed the post where he directed profanity at me and called me a liar (again).

But hey, if I hear of an opening on the IMEL*, I'll let you know.  Honestly, dude.  ::)

* Internet Morality Enforcement League


Did you every consider that if you didn't run around antagonizing people, none of that kind of crap would happen in the first place? You purposely GOAD people to the breaking point, constantly, day in and day out. Why aren't the mods doing anything about that?


This place would be FAR more peaceful if you would just leave people alone. Regardless of how wrong they may be.

40
nobody said that it is impossible.  well i sure don´t. ::)

neuroanatomist is twisting words again (he does that very often) or just simply lying to make a point.

What you said was;

i doubt they move something physically 16000 times a second.

What the linked article states is:

Quote
Every single pixel can take the full color info with the help of an electrified moving color filter!

So, apparently you believe the article you linked is lying.  Or, as you also stated, the author of the article is clueless about how it works.  In that case, what was the point of creating this thread?  Oh yes, you're a troll...and a slanderer as well.


Do you enjoy emberrasing and belittling and degrading people? Honestly, dude. The whole entire article is likely a fraud, so YES, the guy who wrote it, or whoever "leaked" it to him, is most likely LYING.


I tried to head off an inevitable useless debate by linking the ISW post on this particular rumor. If you look at the comments, the guys there (who, as I stated, are very often sensor designers themselves) think the specs are fake. They also seemed to believe the design was for a layered sensor, not something "out there" like as 16Khz oscillating CFA.

41
Ahhhhhh.....

I misunderstood....

Do you know if anyone has tried to make a sensor with microprisms instead of microlenses? That would seem to me as an interesting way to use more of the incident light....


Panasonic has:


http://mikepasini.com/corners/2013/02/04-micro-color-splitters/index.htm


Not necessarily microprisms...at that scale, based on the patent, it sounded like they were using some kind of diffractive deflection, but that ultimately achieves the same thing in the end.


I think this is one of the best ideas I've seen so far. It isn't a stacked sensor, yet it still preserves all the light. Ingenious, if you ask me.

42
Photography Technique / Re: High shutter speed, low aperture but what ISO?
« on: November 12, 2014, 03:33:50 PM »
I totally agree with this.

Well, I disagreed with pdb, so maybe you agreeing with me was to be expected :-p. But I still feel I might have finally got something right around here :-)


Oh, no! I agree with you because I agree with you. Despite how some may portray me, I am not petty like that. I have no interest in agree with anyone as a means of disagreeing with someone else. If I disagree with someone...well, I disagree with them openly (I think everyone on these forums knows that by now.)


I don't know you as someone who gets things wrong...your very knowledgeable in my book. You are a great source of ML knowledge in particular, and I think that's great. I think your spot on with your comment here about ISO as well.


I always find it interesting that somehow some concepts, which really don't seem difficult or complex to me, are often portrayed as "too difficult" for the average photographer. As far as I am concerned, if someone is using a DSLR day in and day out, then learning a little bit about the nuanced behavior of ISO settings can only help them produce better results. Why hold knowledge back?


You are absolutely correct that pushing ISO higher and higher to get a "correct" exposure may be costing the photographer dynamic range. Dynamic range is just as important at higher ISO as it is at lower ISO. These days I think dynamic range is as important for my bird and wildlife photography as it is for landscapes. Ever photograph a chickadee? Brilliant bright white paired up with dark blacks. Doesn't really matter how you approach a subject like that...something, somewhere, is going to suffer. It's difficult not to clip the highlights of those little birds (assuming you want any amount of detail in the black feathers...otherwise you just block up the black feathers into pure black, no detail at all...personally, I don't like that option), especially when you usually need shutter speeds over 1/1000s to freeze their constant motion. Sometimes, underexposing at a lower ISO is necessary to protect those highlights, and still get the shutter speed you need.


So, I really do agree with you. And I agree with you because I think your correct. ;)

43
Like I said...not revolutionary and likely irrelevant for dSLR/MILC.

people said the same about BSI sensors.
they will only be used in smartphone and tiny sensors.

or exmor.. how many said that´s useless.

well a few years later everyone wants exmor sensors.

 
 
What people said about backlit sensors in 2008 were that it was more effective for small sensors, but with a few years of development, that might change.  Its still true, as the sensor gets larger, given the same pixel sizes, backlight technology is not as useful.  For very high MP sensors where there is not enough room for wiring on the front side, than moving the wiring to the back allows for larger photosites which is a definite help. 
 
So, yes, years later, BSI technology is finding its way into larger sensors each generation.


It's already found it's way into a 1.5x crop APS-C sensor with Samsung's NX1 camera.

Yes, Samsung was one of the early companies to start working on BSI.  I think that we will eventually see it even on MF sensors when the MP count climbs so high the the wiring is causing a issue.
 
I think that the 35MP point on FF starts to see a slight advantage, and at 50-60MP, it might be enough to make a big difference.  I hope Canon does it before then, even a small reduction in noise helps.


If Canon is moving to layered sensors, I believe they will be BSI. The more recent patents we have seen from them regarding layered sensors showed BSI designs.

44
Quote
......
– Records 2K with 16,000 frames per second.

So a 7D2 at 2K 60Hz video cranks out 440Mbytes per minute.... At 16000 fps that becomes 117,333Mbytes per minute or a mere 1,956Mbytes per second. My 32Gbyte CF card would hold 16.3 seconds worth of video....

I think I need a bigger card :)


Are those values for RAW video? Generally speaking, you can gain massive compression ratios with video, and at such high frame rates, the differences between frames are going to be quite small, so I would expect the compression ratio to be even higher.

45
Photography Technique / Re: High shutter speed, low aperture but what ISO?
« on: November 12, 2014, 01:21:07 PM »
Never intentionally underexpose and then try to raise exposure in Lightroom.

I disagree because...

Always choose higher iso and brighter exposed shot. Dealing with well exposed noise is much easier than dealing with underexposure and noise.

... unless the iso value you're dealing with is just digitally amplified (usually above 3200 or 6400, varies among models) - in that case, increasing iso just cuts away dynamic range.

One additional benefit of underexposing a bit on lower iso is highlight safety in varying higher contrast outdoor light. If your camera metering misses with a "properly" exposed setting, the whites are blown. ymmv with what camera metering you use, but my 6d is dodgy so I'd rather play safe.

The problem esp. with my 60d's crop sensor is that higher iso values destroy color accuracy, so personally I rather underexpose 800 a bit than raise to 1600 or even 3200. You can always try to get rid of noise in post, but preserving colors after the fact is difficult. Again ymmv depending on the scene and your camera model.


I totally agree with this. There is a point of diminishing returns as far as pushing ISO goes. Once you hit the read noise floor, using higher and higher ISO settings is going to start severely impacting your DR, for practically zero gain on the noise front. Technically speaking, using ISO 12800 is better than using 6400 because your still amplifying the signal before read noise is introduced, but on current cameras read noise at those ISOs is usually <3e- anyway, so the difference between ISO 6400 and 12800 is by far the loss in dynamic range (by orders of magnitude). You could easily shoot at ISO 6400 and lift in post, and not notice any difference as far as shadow noise goes...however if you clip the signal at ISO 12800, your better off using ISO 6400.

Pages: 1 2 [3] 4 5 ... 309