Why bother changing base ISO?

Started Jul 18, 2007 | Discussions
kevm14 Senior Member • Posts: 2,253
Re: There's no red data in the sky

Tom Christiansen wrote:

Even a "clear blue California sky" is going to have a red-channel
multiplier. And just how much red signal can there be in a blue
sky anyway? It's the same problem as blue channel in incandescent
light. You have very little signal to start with, boost it 3 stops to go
from ISO 100 to pseudo-ISO 800 equivalent, then further add
distortion by a white-balance coefficient. GIGO, magnified.

But that was a daylight shot, so working from a daylight WB perspective, the red channel wouldn't have had to be pushed to obtain the correct WB. I don't see why the sky should be noisier in the ISO100 shot pushed 3 stops vs the 800 shot.

Julia Borg Veteran Member • Posts: 7,280
Re: Adobe problems

Julia, might you happen to have any idea why Adobe converters
seem to do worse on Nikon noise than Nikon's converters do?

I tried to figure that out. it seems that applying of white balance to RGB data through matrix transform is introducing more noise then applying multiplication to individual channel data before demosaicing. btw using multiplication only 2 channels are affected, while with chromatic adaptation over RGB data all three channels are affected and introducing additional cross-noise (noise from weak channel affects stronger channels during demosaicin, and then, additionally, during chromatic adaptation).

RML demosaicing acts separately on luma and chroma; and then restores exact values of channel data where possible. Adobe way does not follow yellow brick road, accuracy is sacrificed for speed. repeating demosaicing each time user changed WB is of course time-consuming.

Does everyone reverse engineer the exact
multipliers needed due to Nikon's idiosyncratic dye-color choices
between bodies by dissassembling Nikon's own converters, or do
they derive these number empirically, and potentially inaccurately?

I used disassembly for my table. however it turned out there are much simpler methods

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Julia

Julia Borg Veteran Member • Posts: 7,280
Re: The promised test photos...a few hours late

cycle61 wrote:

Julia Borg wrote:

figured there might be something wrong with my
methodology

no, not your methodology is wrong - it is just that Adobe converters
are not suitable for this kind of work.

What converter do you suggest?

try NC/NX IMHO the native software should be a benchmark to judge the quality of 3rd-party solutions.

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Julia

Julia Borg Veteran Member • Posts: 7,280
Re: There's no red data in the sky

But that was a daylight shot, so working from a daylight WB
perspective, the red channel wouldn't have had to be pushed to obtain
the correct WB.

it has to be pushed; and pushed heavily. Dan Margulis observed the following: " No digicam I've ever tested consistently produces a good red channel in skies without resorting to excessive blurring elsewhere".

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Julia

cycle61 Senior Member • Posts: 1,550
Re: There's no red data in the sky

kevm14 wrote:

Tom Christiansen wrote:

Even a "clear blue California sky" is going to have a red-channel
multiplier. And just how much red signal can there be in a blue
sky anyway? It's the same problem as blue channel in incandescent
light. You have very little signal to start with, boost it 3 stops to go
from ISO 100 to pseudo-ISO 800 equivalent, then further add
distortion by a white-balance coefficient. GIGO, magnified.

But that was a daylight shot, so working from a daylight WB
perspective, the red channel wouldn't have had to be pushed to obtain
the correct WB. I don't see why the sky should be noisier in the
ISO100 shot pushed 3 stops vs the 800 shot.

The shot (obviously) was clear daylight, with a cloudy WB selected (sorry, my mistake. I didn't change it in ACR because that would introduce yet another variable to the equation) The reason the ISO 100 shot is noisier is because a limited amount of digitized data is being expanded to cover the entire range, where with the higher ISO, the analog signal is amplified prior to digitization, providing smoother tonality (apparently up to ISO 800).

By the way, my altitude was somewhere in the range of 20-40 feet above sea level. I wish I had your problems, trying to get my WB right while being stuck in the mountains all the time.
--
-Nick Davis
Please feel free to critique anything I post. I'm here to learn.

My galleries, such as they may be...
http://www.pbase.com/cycle61

Julia Borg Veteran Member • Posts: 7,280
Re: There's no red data in the sky

Even a "clear blue California sky" is going to have a red-channel
multiplier.

it is common knowledge that to get dramatic sky look we are using orange/red filters shooting b/w. try blending red channel into skies (luminosity mode). that is how to get a wow look

if the sky is blue, the details (both contrast and noise) are mostly contained in the "unwanted" red channel. same, the red rose contains details in the "weak", "unwanted" cyan/blue. it is extremely important to have a good clean "weak" channel, otherwise what we are getting is color blobs without contrast and detail. skin needs a good cyan/blue channel too (one of the reasons why shooting portraits under halogen lights is getting progressively less popular with digital spread).

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Julia

cycle61 Senior Member • Posts: 1,550
Re: The promised test photos...a few hours late

Julia Borg wrote:

cycle61 wrote:

Julia Borg wrote:

figured there might be something wrong with my
methodology

no, not your methodology is wrong - it is just that Adobe converters
are not suitable for this kind of work.

What converter do you suggest?

try NC/NX IMHO the native software should be a benchmark to judge the
quality of 3rd-party solutions.

Does anybody else want to take a whack at this? I don't have either of these programs right now. If pbase will host .nef files, I'll happily upload some new originals taken with NR off and the right WB at 3200 down to 800, or 100. Are there any third party raw converters out there preferable to Nikon's? I have the damnedest time getting their software to work well on my machine.
--
-Nick Davis
Please feel free to critique anything I post. I'm here to learn.

My galleries, such as they may be...
http://www.pbase.com/cycle61

Jeff Folkins
Jeff Folkins Contributing Member • Posts: 853
uniWB histrogram all the time

Raul

yes, certainly. The clipped highlights of the green channel on your uniWB example certainly look like a problem. Don't you think? So underexposing (negative EV) would save the day, right?

Personally I wish Nikon would display the equivalent uniWB histogram all of the time so people could really figure out if they were blowing the highlilghts. I don't like keeping my uniWB active because the people all look green on the display. This would be a nice option... Nikon, please, show us the real historgrams.

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tko Forum Pro • Posts: 12,796
yes

That what makes it so surprising. The tests I saw were for prosumers, perhaps they aren't as sophisticated as a dSLR, but it's still very surprising.

cycle61 Senior Member • Posts: 1,550
Re: There's no red data in the sky

Julia Borg wrote:

But that was a daylight shot, so working from a daylight WB
perspective, the red channel wouldn't have had to be pushed to obtain
the correct WB.

it has to be pushed; and pushed heavily. Dan Margulis observed the
following: " No digicam I've ever tested consistently produces a
good red channel in skies without resorting to excessive blurring
elsewhere".

Red channel definitely suffered the most in this shot, here's the red channel only for the ISO 100 and 800 crops:

Pretty telling, that you definitely do lose out by not using the full tonal range of your A/D converter.
--
-Nick Davis
Please feel free to critique anything I post. I'm here to learn.

My galleries, such as they may be...
http://www.pbase.com/cycle61

Julia Borg Veteran Member • Posts: 7,280
Re: There's no red data in the sky

Red channel definitely suffered the most in this shot, here's the red
channel only for the ISO 100 and 800 crops:

please e-mail me the nefs

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Julia

Julia Borg Veteran Member • Posts: 7,280
Re: uniWB histrogram all the time

Personally I wish Nikon would display the equivalent uniWB histogram
all of the time

... also skipping all in-camera settings, like tonal curve, saturation, and sharpening; so that we can skip loading hacks into the camera and shoot with useful settings...

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Julia

Pierre Sottas Contributing Member • Posts: 787
Re: uniWB histrogram all the time

Jeff Folkins wrote:

Personally I wish Nikon would display the equivalent uniWB histogram
all of the time so people could really figure out if they were
blowing the highlilghts.

Yep. And a matrix metering mode that preserves the highlights would be even better -> to meter so that the most luminous part of the scene corresponds to the right of the uniWB histograms.

The camera should figure out if highlights are blown, not me

Pierre

Julia Borg Veteran Member • Posts: 7,280
Re: uniWB histrogram all the time

a matrix metering mode that preserves the highlights would
be even better

only as an option. in many cases it is impossible to held highlights and to get decent clean image in midtones, much less in shadows.

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Julia

Fotomat Senior Member • Posts: 1,220
Re: There's no red data in the sky

Sorry if this is off topic but what's a good filter for sodium-vapor lights? ..doing some night photography
--
Fotomat

Derouyag
Derouyag Contributing Member • Posts: 824
Re: uniWB histrogram all the time

Could this be done with a menu option and an upgrade to the firmware (rather than a new camera)?

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Pierre Sottas Contributing Member • Posts: 787
Re: uniWB histrogram all the time

Julia Borg wrote:

only as an option. in many cases it is impossible to held highlights
and to get decent clean image in midtones, much less in shadows.

it should be ok for scenes with less than 10 stops of DR. I'm sure this would be my favorite metering mode

Pierre

Pierre Sottas Contributing Member • Posts: 787
Re: uniWB histrogram all the time

Derouyag wrote:

Could this be done with a menu option and an upgrade to the firmware
(rather than a new camera)?

this should be very easy to implement since this is a very special case of the full matrix metering mode.

Pierre

Julia Borg Veteran Member • Posts: 7,280
Re: There's no red data in the sky

Fotomat wrote:

Sorry if this is off topic but what's a good filter for sodium-vapor
lights?

I need to know your camera model at least, better - to have a nef file with the typical scene. sodium-vapor lights are not continuous-spectrum. low pressure olamps are very close to monochromatic emission of nice golden 590nm and images turn good being toned blue, sepia, or gold. high pressure lamps emit broader spectrum and might allow color images.

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Julia

Raul Veteran Member • Posts: 8,421
Dear Jeff

I find that that uniWB histogram suits me better than the others. I use RawMagick and I believe that I am not loosing any highlights there.

Kind regards

Raul

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