Dark Current Enable Tool

[astronomer]

[whwang]

Hi,

May I ask more about the IFD tag? What is it? I can't find it in dcraw's man page.
Both DSS and PixInsight use dcraw to decode RAW files, and the images stacked by them have the extra pixels.
Do you mean this IFD tag can help PixInsight or dcraw to crop the images correctly?

[russ01]

I have discovered a bug with the dark current ebabler tool on the Nikon D600. While I was taking a heap of test images the othrr night I was pressing the play button to show the image preview on the D600 LCD screen after every image. Sometimes pressing that button causes the LCD screen to light up but stay black. When this happens the camera would freeze and the only way to power off the camera was to remove the battery. This meant that every time this bug happened I would have to plug the camera back into the PC and inject the dark current enabler tool again. Does anyone have any idea why this bug is occuring and if there is anything I can do to prevent it from happening?

[Francois]

[astronomer]

[joel]

Hi all,
just tested the dark current enabler tool on my D90. Looks like it is working OK
- a dark picture (30 secs) is now containing hot pixels, with a real background level (not zero i mean, which is what you obtain without this tool)
- an offset (1/4000s) picture contain also some signal (~256) while without this enabler the signal is equal to zero
- tone is magenta
- NEF file size is way bigger (~20Mo) than without the patch.


Thanks a lot for this hack...will now try this on some astro pictures... just missing a usb driven bulb to have a complete nikon "astro camera" !!
Joël

[joel]

Hi all,astronomer

Maybe something informative for the D90 owners using iris software (from christian buil) and this "patch" for their astro photo :
If you load the nef file as D90 files then they will be wrongly decoded for the bayer pattern and the RGB conversion will give you wrong color at the end.
You should load them as if they are D100/D300 NEF files.
Also, with the initial tests i made the custom balance should be set somewhere close to Red=1.63, Green = 1.0 Blue =1.135 (rough test made on a white paper, cloudy day)
Regards

[Ohansmit]

Just registered on here to say thanks

Ive only captured images with this mode and they come out very well and noise free on the D800 unmodified.

Thanks

[yutor]

Hi all, astronomer!

Playing with Nikon D810a.
Nikon did it wrong again.
No "fair", unprocessed RAW (NEF) again.

They use some algorithm to scale/offset data based on signal from "dummy" (for bias) and "optically black" (for dark) pixel columns.
With this mean value for any dark exposures (with reasonable ISO and duration up to 900 seconds) is close to 600ADU...
Left "wing" of pseudo-Gauss histogram distribution is cut and filled with some value (equal to scaled bias?).

Histograms of master bias (x128) and master dark (900sec, x15) for ISO800 are shown.


Nikon D810a ISO800 Master Dark & Bias Histograms by Yuriy Toropin, on Flickr

Another point to mention - there is no real HOT (saturated) pixels on the master dark at all. The maximum value in CFA is ~5000.
Looks like they could additionally filter out saturated hot pixels.
Or - may be they specially select only the perfect sensors for D810a, without hot pixels at all?! Thanks, Nikon!

I've tried Mode 3 (switch ON Long Exp Noise Reduction mode, then turn camera off during Job NR). Surprisingly, I've got only 1 (one) frame with "nice" histogram out of 6 tries.
Something goes there also.

***
Anyway, dark current enable tool is needed for the Nikon's D810a real "astrocamera".

astronomer, is it doable? Can I somehow help you with this?
(Own D750, have D810a on testing from Nikon local representative office)

[astronomer]

Hi,

The behavior of D810/a, D750 and lower end D5300/3300/5500 is as what you described.
I think it's due to the subtraction taking place in unsigned integer space and shift right with some value.

For the work around, I can't do anything unless the image adjustment software for these camera is leaked.
There's an adjustment entry called "Dark Current" in it which changes the image processing register on the EXPEED RAW front end.