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#apertus IRC Channel Logs

2016/01/21

Timezone: UTC


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se6astian|away
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06:49
se6astian
good morning
07:07
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darthrak_
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07:46
intracube
so that bottom right discolouration here: http://i.imgur.com/j23B4rt.png
07:47
intracube
is visible in the nonlinearity images after a contrast stretch: http://i.imgur.com/S8g32Eo.jpg
07:47
intracube
only in the green channel, though
07:48
intracube
a diff of green with either red or blue channel + further contrast stretch: http://i.imgur.com/3Qvbd1x.jpg
07:48
intracube
^ alexML
07:54
alexML
yeah, I need a better clip frame (I'm experimenting with something that accounts for nonuniform illumination of the wall, but no meaningful results yet)
07:55
intracube
isn't that green a sensor issue rather than scene illumination?
07:56
alexML
I'm also trying to recover the response curve with other methods; unfortunately, with existing programs like mkhdr or pfshdrcalibrate, I've got only bogus results
07:56
alexML
so I'm reinventing the wheel :P
07:56
intracube
heh
07:56
alexML
it's not a sensor issue, it's just the calibration frame
07:56
intracube
oh ok
07:57
alexML
(I'm working on existing samples, remember)
07:57
alexML
(I don't have a beta yet)
07:57
intracube
^ soon though :)
07:58
alexML
I also thought at something that would flip the exposure back and forth near the clipping point - if I let that run for a while, I guess it should give pretty exact per-pixel curves
07:59
alexML
(there is plenty of noise in that region)
07:59
intracube
you mean the granularity in the highlights (particularly saturated areas)?: http://i.imgur.com/qVfdkGs.jpg
08:00
alexML
yeah
08:00
alexML
that throws off the calibration, so if I want to get per-pixel curves from the existing dataset, there's a ton of noise in the data
08:01
alexML
but if you repeat that experiment 16 times, that noise would be reduced by 2 stops
08:01
alexML
if you repeat it 64 times => noise reduced by 3 stops
08:01
alexML
and so on
08:01
intracube
so in theory, it could be reduced a fair bit
08:02
alexML
well, I want to get the exact (unbiased) curves first
08:02
alexML
so the noise would have zero mean (that is, so it won't introduce color casts)
08:02
alexML
once you have good average colors, you can just denoise those highlights a bit
08:03
alexML
and then there's the repeatability issue
08:03
alexML
that needs to be checked, how it varies with exposure, temperature, whatever
08:04
intracube
and this profiling would have to be done for each individual sensor
08:04
alexML
and if it's just a simple offset, maybe it can be detected on the fly
08:04
alexML
yeah
08:04
intracube
and also possible changes as the sensors age
08:04
alexML
same for dark frames
08:04
Bertl_oO
changed nick to: Bertl
08:04
alexML
yeah, I want to have these calibration routines in the camera
08:05
intracube
is this extreme non-linearity in the highlights typical for cmos?
08:05
intracube
I thought it was generally linear
08:05
Bertl
it isn't a problem of the photo sites, it is a problem of the ADC and gain
08:06
alexML
on Canon, it seems to clip quite harshly
08:06
intracube
Bertl: ah
08:06
alexML
on 5D3, I turned down all the gains I could identify, so it no longer clips to white
08:06
Bertl
or to be precise there are several effects going on
08:06
alexML
and got some fixed-pattern noise in highlights
08:06
alexML
but after correcting that, there was no useful data to recover, like on the CMV
08:07
Bertl
first, the CMOS charges a capacitor to a certain level
08:07
Bertl
then the photo diode discharges it when light is received
08:07
Bertl
this process is not really linear per se
08:08
intracube
ah ok
08:08
Bertl
also, it has a roll-off when the capacitor reaches zero voltage
08:08
Bertl
because the diode adds a certain offset there as well
08:08
Bertl
assuming that the actual sensel is operated in the linear range
08:09
Bertl
(or to be precise, in the range where it acts as expected)
08:09
Bertl
you'll get a nice and proper voltage to digitize
08:09
Bertl
this is where the second stage brings in non linearities
08:10
Bertl
i.e. you apply analog gain, which has nonlinearities at the rails
08:10
Bertl
and you also run the ADCs, which again have (usually quite small) nonlinearities at the limits
08:11
Bertl
given that everything is optimal, you will only see a proper linear range
08:11
Bertl
the CMV is a little odd in this regard, as it allows for a number of analog gains, which are well below the ADC range
08:11
Bertl
this
08:11
Bertl
per se is not a bad thing
08:12
Bertl
it just means that the full 12bit range will not map to a linear range in all gain settings
08:16
intracube
interesting, thanks for the explanation :)
08:17
Bertl
you're welcome!
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se6astian
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Bertl
off for now ... bbl
15:42
Bertl
changed nick to: Bertl_oO
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se6astian|away
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18:49
se6astian
anyone currently here speak spanish?
18:51
Bertl_oO
Lo sentimos, no hablo español! :)
18:52
Bertl_oO
or maybe better? ¡Lo siento, no hablo español!
18:55
intracube
dos cervezas, por favor
18:56
Bertl_oO
LOL
19:08
troy_s
Bertl_oO: Yo
19:09
troy_s
Bertl_oO: intracube noticed that there's some odd glow in the lower right corner. Any clue as to what this might be? Light leak / splash off of an LED? Heat? Electronics?
19:09
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19:09
troy_s
Bertl_oO: http://i.imgur.com/S8g32Eo.jpg
19:10
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19:20
alexML
troy_s: that corner was not completely overexposed, but the rest of the image was (obvious if check the other images in the set)
19:21
troy_s
alexML: I don't mind. I'm more interested in what causes it.
19:21
alexML
once you go past some overexposure level, the sensor output starts to decrease
19:21
troy_s
I'm more interested in the fact that it is there at all.
19:21
troy_s
And why.
19:21
troy_s
Could be an LED leak like was had in the early Alpha.
19:22
troy_s
Or heat, or magnetic magic fubar or who knows.
19:22
alexML
check the nearby samples (render them in the same way and play the movie)
19:22
alexML
you will no longer blame cosmic radiation after you do that :P
19:24
intracube
http://i.imgur.com/F0oLpFD.png
19:25
alexML
check from 30 to 90ms for example
19:25
alexML
or, even better from 1ms
19:26
troy_s
alexML: I don't blame anything. I'm just leaving everything open. Those shots are hooped.
19:26
troy_s
It is upper right too.
19:26
troy_s
So could very well be an LED leak off of one of the boards.
19:26
troy_s
Or any other thing.
19:27
alexML
it's not visible in dark frames, so I doubt it's a LED leak
19:27
troy_s
Dunno.
19:27
troy_s
That's my point.
19:27
troy_s
Bertl will have good insight.
19:27
alexML
but please - see the entire sequence before judging
19:27
troy_s
How come?
19:28
troy_s
Does it flicker?
19:28
intracube
I thought the 'nonlinearity-gain1x-offset' images were dark frame?
19:28
alexML
no, they are not
19:28
troy_s
Anyways... off to pick up damn Cintiq number THREE for the love of god.
19:28
intracube
ooh
19:28
alexML
they are a blank out of focus wall
19:29
troy_s
Dark frames are portal capped images then?
19:29
troy_s
(I take it)
19:29
intracube
ok, that does change things slightly. but this issue only seems to be on the green channel
19:29
intracube
nothing on red or blue
19:29
troy_s
That's odd.
19:29
troy_s
If that's true then it is a magical source.
19:29
intracube
will have a look at the darkframes
19:30
troy_s
To only impact one data channel would be pretty damn magical.
19:30
alexML
they all behave the same electrically, but green is usually receiving more light (hint: white balance)
19:30
troy_s
White balance?
19:30
troy_s
This is off of the raw data.
19:30
troy_s
So how would white balance even factor in pre-transform?
19:30
alexML
yes, if you render raw data without white balance, what color cast do you get?
19:30
troy_s
You don't get any colour cast
19:30
troy_s
There's no colour.
19:31
troy_s
You might as well be dumping a musical track to an sRGB screen.
19:32
intracube
just to confirm; I'm not seeing anything on a dark frame image
19:32
intracube
(darkframe-100ms-gainx4-10.raw12)
19:33
troy_s
intracube: Then it must be across all data channels if it is a leak
19:34
intracube
yep, unless it is a fairly pure green light from somewhere
19:34
intracube
but you'd expect to see something on the other channels, I guess
19:34
alexML
again, it's a blank wall
19:35
alexML
in the middle of the image, r=g=b (roughly, on raw channels, no colorimetry)
19:35
alexML
in that corner (not yet clipped), green starts to clip, red and blue are lower
19:35
troy_s
alexML: So it's a leak?
19:35
alexML
what color do you get when you render with wb multiplers 1,1,1
19:35
alexML
no
19:36
alexML
it's not a leak
19:36
Bertl_oO
well, I was wondering about the corner as well (on the image intracube "corrected")
19:36
troy_s
Bertl_oO: More like amplified.
19:36
alexML
that's how a white paper appears when it's close to overexposure, and uniwb
19:36
troy_s
It's got to be a leak.
19:36
alexML
try it on Canon, Nikon, whatever you want
19:36
troy_s
If it isn't on the dark frame, and it is on the other non-darks
19:36
troy_s
It is a leak of some sort.
19:37
alexML
it would look very similar
19:37
Bertl_oO
but then I saw the other image somebody visiting sebastian made from the setup
19:37
troy_s
Bertl_oO: And?
19:37
troy_s
Bertl_oO: Difference?
19:37
Bertl_oO
and in this image, there is a bright light source on the left, and a table lamp on the right, just illuminating that corner
19:38
troy_s
Flare leak.
19:38
troy_s
Or just a literal light
19:38
troy_s
I didn't think twice when I first saw it and just assumed it was a glow from a lamp.
19:38
troy_s
It's not shaped enough to be a flare, but it is also in the top right corner too.
19:38
troy_s
Slightly.
19:39
Bertl_oO
so, I would double check with sebastian, that the setup is not flawed here before discussing this effect further
19:39
troy_s
It has falloff like a lamp.
19:39
troy_s
I agree.
19:39
troy_s
I mean as far as I am concerned anyways, it's all moot until the next iteration comes in with proper latitude.
19:39
troy_s
Not much to be done until then.
19:40
troy_s
Bertl_oO: Would you be able to get a camera set up such that it could be remotely controlled?
19:40
troy_s
Just to tweak the PWLC etc?
19:40
troy_s
(God. Must go get Cintiq Blech.)
19:40
intracube
troy_s: I forgot to mention... I blurred the images to get rid of HF FPN too
19:40
intracube
so don't read too much into the shape of it
19:42
alexML
again - take an image of a blank wall, with any digital camera, overexpose it, leave just one corner a little unclipped, and render the raw file in the same way
19:42
alexML
upload the result here
19:43
Bertl_oO
troy_s: I'd say we already have part of that in place
19:44
Bertl_oO
with a bunch of remote controlled switches to change the lighting, it should probably work
19:44
Bertl_oO
the Beta itself is already remotely accessible
19:46
troy_s
Bertl_oO: should put a rotate data channels into the format so folks done erroneously call them colours
19:47
troy_s
Bertl_oO: with a calendar we could have a nice lab
19:48
troy_s
Very keen on PWLC
19:49
troy_s
Would be a terrific way to test calculated knee points
19:49
alexML
troy_s: we are looking at low-level sensor output, before the matrix gets applied
19:50
troy_s
(Reverse a log step per bit per stop optimization to knees)
19:50
troy_s
I know this
19:51
alexML
I doubt that :P
19:51
troy_s
Notice how I never say colour when looking at data?
19:51
alexML
yeah, how should we call it?
19:51
troy_s
Data
19:51
intracube
red: http://i.imgur.com/lFH9rOq.png green: http://i.imgur.com/qAhCrX1.png blue: http://i.imgur.com/aun2ttc.png
19:52
intracube
troy_s: this is the data off the r, g, b sensels though. so you can legitimately call them that
19:52
intracube
those images contrast all contrast stretched the same amount
19:53
niemand
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19:53
troy_s
Which has no reference so you may equally call them radish, turnip, potato
19:54
intracube
no reference? the sensels have colour filters, no? :)
19:54
troy_s
Yes but no reference
19:55
troy_s
If you rotate those channels the data is equivalent
19:55
alexML
troy_s: to be able to rotate the channels, you first need linear response (not clipped stuff)
19:55
alexML
we don't have that here, so we can't rotate yet
19:56
alexML
we are just looking at the raw data before rotating
19:56
alexML
that's it
19:58
alexML
intracube: you have applied white balance to the data
19:58
alexML
can you show the raw (unmodified) one?
19:58
alexML
maybe r,g1,g2,b
19:59
troy_s
Say what?
19:59
intracube
alexML: this was with Bertl's script. I didn't think it did any white balance
20:00
intracube
and just debayered
20:00
troy_s
If you rotate those channels and profile it will deliver guess what
20:02
intracube
convert \( -size 4096x3072 -depth 12 gray:input_raw_image.raw12 \) \( -clone 0 -crop -1-1 \) \( -clone 0 -crop -1+0 \) \( -clone 0 -crop +0-1 \) -sample 2048x1536 \( -clone 2,3 -average \) -delete 2,3 -swap 0,1 +swap -combine output.png
20:02
intracube
^ alexML
20:03
intracube
doesn't fully understand how it works :)
20:04
alexML
intracube: nevermind, can you do the same thing for the other images in the set?
20:05
alexML
let's say from 1 to 100ms
20:05
troy_s
Anyways had my fun in the asylum.
20:05
alexML
in particular, compare the 75ms one with the 88ms one (since I didn't download past that)
20:05
alexML
compare all 3 (or 4) channels
20:05
intracube
alexML: I'll have a go later, yep
20:06
intracube
need to get some food in a bit
20:10
troy_s
Did you rotate the channels and characterize yet? ;)
20:11
alexML
troy_s: this is an overexposed image, what do you expect?!
20:12
troy_s
I expect the exact same results actually.
20:12
troy_s
Rotated primaries ;)
20:12
troy_s
12:55 <alexML> troy_s: to be able to rotate the channels, you first need linear response (not clipped stuff)
20:12
troy_s
That is crap
20:12
alexML
proof please
20:13
alexML
(as in, apply the matrix on a nonlinear image and show that you get correct results)
20:13
troy_s
Not the damn matrix
20:13
troy_s
To characterize.
20:13
troy_s
Hence why I keep repeating they ain't colors.
20:14
troy_s
Anyways... Fun time is over. This is depressing.
20:34
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20:44
Bertl_oO
intracube: do you want to know how it works? :)
20:47
Bertl_oO
if so, please remind me when I'm back from my nap ...
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Bertl_oO
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se6astian
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se6astian
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