Hot pixel removal without darks

[fmazzanti]

i guess if you care so little about the quality of your data that you are not willing to make a few darks, then why bother with any of this?

Uhmm... nice way of putting things.

look, my point is that you only need a handful short darks integrated together to get a good map in CosmeticCorrection. as others have pointed out you don't actually need the dark, but i figure why not use the dark to guide the CC process? the dark contains the truth. you can guess which pixels are outliers (which is all AstroArt and even CC is doing without the dark) or you can just go right to the source.

taking one or two darks every once in a while is a far cry from making a 50-100 frame dark master or taking a billion darks every night. so i don't really see why it's a huge burden.

by the way these sensors are stable enough that you can probably use the same dark for months and it will be perfectly fine for the purposes of identifying hot pixels.

rob

That was not what I understood from tour message. I do not use darks, but they have to be the same time length as your lights, right? So if you grab 10+ min exposures, it'll take some time... Or is it that they don't need to be the same time length as the subs, just for the cosmetic correction thing?

Thanks,

Ferran.

[mcgillca]

I think the key reason for not using darks with these chips is that the dark current is so low (0.0015 e/pixel/s - about 1 electron per 10 minutes) that using darks in the main processing flow would create noise rather than reducing it (they would essentially be 10 minute bias frames - you'd need a lot to reduce the noise to the same as your master bias frames).

I use dither and then clipping to remove them, but as Rob said, if you had a few that you could use for cosmetic correction, that could work well, although as others have said, you can do the same thing using the existing tools.


Colin

[topboxman]

CosmeticCorrection doesn't need dark frames. It can use them but it can work very well without them using the "Auto detect" mode.

+1 what Andres said. I have used Cosmetic Correction without any dark frames and works very well. My camera is also ICX-694 based (QSI 660wsg).

Cosmetic Correction is very simple but can be confusing for first time user.

Peter

Aha, thanks... I can try that and see what can it do for me. Have you tried also with the dark frames, to check what real difference it does with that chip?

Thanks a lot,

Ferran.

Yes I have and it does not appear to make much difference. Darks may be better for Kodak chips since they are noisier than Sony's.

Darks are easy to capture and can be done anytime. It's always wise to have darks available to see if they are more beneficial.

Peter

[sreilly]

Maybe you're looking at this differently then need be. My ST-10XME hasn't been used in a couple of years and I'm getting ready to start using it again. I took the camera into my office and put it on the floor below my desk in a dark corner and hooked the USB cable up to my computer. I assume that because you are doing your imaging "in the filed" that you are using a laptop. Simply hook your camera up to the laptop in a cool dark spot and take some darks. Nothing else need be connected. I've done darks and bias frames like this for years. Even though I have an observatory, sometimes during the day it too warm to get the cooler down to where I'll be imaging that evening so I simply unmounts the camera and bring it into the warm room which in summer is now the cool room, I have a small 5,000BTU a/c in there.

I've been using a dark and bias library for years because I can take these whenever I see a need and especially on days/nights I know I can't image. I take them for the duration I image and at the same temperature, 10, 15, 20, and 30 minutes. I usually do increments of 5 degrees with -30 being the lowest and -10 the highest. I use these until I see they no longer work well. In my case with my STL-11002M I take my bias frames at the same temperatures as my images so they are grouped the same way as my darks.

-Steve

[pfile]

i guess if you care so little about the quality of your data that you are not willing to make a few darks, then why bother with any of this?

Uhmm... nice way of putting things.

look, my point is that you only need a handful short darks integrated together to get a good map in CosmeticCorrection. as others have pointed out you don't actually need the dark, but i figure why not use the dark to guide the CC process? the dark contains the truth. you can guess which pixels are outliers (which is all AstroArt and even CC is doing without the dark) or you can just go right to the source.

taking one or two darks every once in a while is a far cry from making a 50-100 frame dark master or taking a billion darks every night. so i don't really see why it's a huge burden.

by the way these sensors are stable enough that you can probably use the same dark for months and it will be perfectly fine for the purposes of identifying hot pixels.

rob

That was not what I understood from tour message. I do not use darks, but they have to be the same time length as your lights, right? So if you grab 10+ min exposures, it'll take some time... Or is it that they don't need to be the same time length as the subs, just for the cosmetic correction thing?

Thanks,

Ferran.

the darks only need to be the same length as you lights if you are trying to remove the thermal signal from your lights... but as i understand it some sensors have such low dark current that there's not much point in calibration, except for bias and flats.

so yeah, i was saying that a short dark, and maybe a master made from just a few of them, would identify the hot pixels to CosmeticCorrection.

who knows, maybe you need a really long dark to hit all the pixels which are not "hot" but only "warm". but either way you probably don't need a very high quality master dark just to identify those pixels to CC.

rob

[CharlesW]

I'm also a tear down and set up imager but all you need to create a vast dark library is your laptop, camera, and a countertop. I appreciate that your camera's noise might be so low that you don't "need" darks but for the time spent debating the fact here you could have had your library finished and it would probably make processing your images a lot more mainstream and easier.