Trick: correctly pushing D800 to higher (ISO) limits

Started Mar 29, 2012 | Discussions
Dominique Dierick Veteran Member • Posts: 4,494
Trick: correctly pushing D800 to higher (ISO) limits
13

People trying to produce raw images at H2 or pushed H2 with the new Nikon D800 have surely already noticed the blue-magenta cast on the image, with a band running along the longer side of the image, caused by amplifier glow. Fwiw, even the D3s shows traces from it at extreme high ISO values. There is a fairly simple method to get rid of it in post processing and start with a much better image color. The alternative is manually start to tweak the image, rather time consuming.

The only thing you need to do is make a bias frame to correct it. It's an image at approx the same exposure and ISO, but with lens cap on and viewfinder closed. You will obtain an image only containing the glow (and noise). No need to each time make one. Make a library of some different temperatures and exposures.

Open the raw images in a good image editor, with exactly the same settings. If you push the source image by a stop, also do so with the bias frame! Now subtract the bias frame (e.g. PS apply image) from your light frame. Perhaps you need to tweak the percentage of subtraction, but it will be minor. The result will be a much better image to start with. Maybe the de-dusting image in the camera could have the same effect (not tried), but this is far more flexible.

The sample show an H2 image, pushed one stop in post to 51k ISO.

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OP Dominique Dierick Veteran Member • Posts: 4,494
Works in normal H2 too of course n/t
1
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Peter Hayward Contributing Member • Posts: 672
Re: Trick: correctly pushing D800 to higher (ISO) limits
1

This is why I come to this forum. Neat. Thanks.
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u007 Senior Member • Posts: 1,681
Re: Works in normal H2 too of course n/t

Dominique Dierick wrote:

Nice tip! Thanks

OP Dominique Dierick Veteran Member • Posts: 4,494
Yep ;)

It can't all be threads about availability at BH or Amazon or comparisons with other brands
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Matsu Senior Member • Posts: 2,272
excellent tip thanks

why isn't my browser letting me bookmark this thread?

Oh well, bookmarked now.

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Heru Fathurohman Regular Member • Posts: 136
Thanks for the tip.

Waiting the delivery in next week

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RP McMurphy Contributing Member • Posts: 571
Re: Trick: correctly pushing D800 to higher (ISO) limits

Great tip...sorry for being a bit of a thickie, but could you expand a bit more about the PS action of subtracting the bias?

Understand the principle and great idea but can't envisage the operation in PS

Thanks

OP Dominique Dierick Veteran Member • Posts: 4,494
Re: Trick: correctly pushing D800 to higher (ISO) limits

Open both images from raw in PS (do not tweak whitebalance on the image!).

Select the normal image. Pick the 'Image-> Apply Image' menu. Select the bias frame as the image to apply, and select 'Subtract' in the dialog box. You can play with percentage subtraction... Easy.

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RP McMurphy Contributing Member • Posts: 571
Re: Trick: correctly pushing D800 to higher (ISO) limits

Many thanks for that Dominique

I'll be trying that as soon as the blasted camera arrives (getting impatient now)

Again, great tip

discopolana Senior Member • Posts: 1,448
thanks, tag D800 shad push/nt

no text

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RicksAstro
RicksAstro Veteran Member • Posts: 3,853
Re: Trick: correctly pushing D800 to higher (ISO) limits

Yup...that's a trick that's been used for years in the astronomy world, and is actually what the camera does when you have long exposure noise reduction on. You're actually doing more towards a dark frame subtraction since it changes based on your exposure. Technically, a bias frame is a frame taken at the shortest possible exposure.

If you do the library idea, it's actually best to average a bunch of frames together to avoid adding random noise to your image.

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OP Dominique Dierick Veteran Member • Posts: 4,494
Yes, I do astrophotography ;)

That's also where I got the idea of applying a bias/dark to correct the color cast.

Didn't really know how to name it, doubting between bias or dark as a name. You can see on the 'bias' I did call it dark to start with The shutter speeds usually are that short, I choose the bias frame name. Darks make me think of long exposures and I don't think anyone in his right mind would to long exposure images at these iso's anyway

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Onetrack97 Senior Member • Posts: 1,953
Re: Trick: correctly pushing D800 to higher (ISO) limits

Makes sense for astronomy but in this case, a fixed object with a supported camera, why not just extend the shutter time?
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OP Dominique Dierick Veteran Member • Posts: 4,494
Re: Trick: correctly pushing D800 to higher (ISO) limits

Makes perfect sense for regular photography. See the samples. Imagine your subject was moving in low light and you push the ISO. This shows you how to get rid of the introduced color cast in a split second. Use it or don't use it

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Zlik Contributing Member • Posts: 990
Re: Trick: correctly pushing D800 to higher (ISO) limits

neat trick, well done and thanks for sharing !

Martin Grecner Contributing Member • Posts: 520
Re: Trick: correctly pushing D800 to higher (ISO) limits

That seems to be a lot of amplifier glow for 1/80s exposure !
My D70 shows amplifier glow at multiple minutes exposures,
and it is one of the worst cameras in this respect.
Definitely not at 1/80s. Even the high ISO does not justify it, I believe...

Dominique, could you please try to make a 5 minute bias frame at ISO800 ?

Thank you very much indeed
Martin

olakiril2 Contributing Member • Posts: 639
Re: Trick: correctly pushing D800 to higher (ISO) limits

Very good idea.
Try averaging multiple black shots before subtracting to eliminate random noise.

xsimplyjosh Regular Member • Posts: 354
Re: Trick: correctly pushing D800 to higher (ISO) limits

wow for iso 25600 (highest iso on d800), it looks pretty usable! unless you added noise/chroma reduction that is :s

Dominique Dierick wrote:

People trying to produce raw images at H2 or pushed H2 with the new Nikon D800 have surely already noticed the blue-magenta cast on the image, with a band running along the longer side of the image, caused by amplifier glow. Fwiw, even the D3s shows traces from it at extreme high ISO values. There is a fairly simple method to get rid of it in post processing and start with a much better image color. The alternative is manually start to tweak the image, rather time consuming.

The only thing you need to do is make a bias frame to correct it. It's an image at approx the same exposure and ISO, but with lens cap on and viewfinder closed. You will obtain an image only containing the glow (and noise). No need to each time make one. Make a library of some different temperatures and exposures.

Open the raw images in a good image editor, with exactly the same settings. If you push the source image by a stop, also do so with the bias frame! Now subtract the bias frame (e.g. PS apply image) from your light frame. Perhaps you need to tweak the percentage of subtraction, but it will be minor. The result will be a much better image to start with. Maybe the de-dusting image in the camera could have the same effect (not tried), but this is far more flexible.

The sample show an H2 image, pushed one stop in post to 51k ISO.

-- hide signature --

Josh - D700 ; Nikon 24-70mm f/2.8G ; SB-900

OP Dominique Dierick Veteran Member • Posts: 4,494
Re: Trick: correctly pushing D800 to higher (ISO) limits

Rest assured, it is. If you go check my threads, I posted one for astrophotography at ISO 1600 and 800 ISO already

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My equipment: Nikon D3s, D800, EOS 450D
The ladies equipment: Panasonic LX5 and GH2 for video

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