Lines in image

[Davey-T]

Just been playing around with some images of the Rosette and they have lines in them.

30 subs stacked in DSS, one RAWs only dark calibrated

The other JPEGs stacked in DSS

Looks like the Bayer matrix as there are also some other feint ones.

Is it a problem or just caused by over stretching the image ?

Ignore all the other faults

Dave

  

[Oddsocks]

Looks like the Bayer matrix as there are also some other feint ones.

Dave

Hi Dave,

Unlikely to be a Bayer mask fault since the mask does not have a series of single colour elements in a straight line, more likely to be a row defect on the detector or non-random noise during detector read.

To isolate this you need to debayer and look at each frame individually for either non-random noise or a row defect.

You will find this easier to do by shooting a few flats rather than astro images and then stretching the resulting frames.

If it is a row defect, reading low levels for an entire row, or no output at all from an entire row, which is not uncommon, then you can only remove the defect from the final image using flats (or dithering the mount between subs), darks and bias frames won't reveal the defect or remove them from the final image.

If it is a row reading low rather than no output at all, especially with CMOS detectors, but also more rarely with CCD detectors then it will be highly variable and dependent on temperature.

Was this with the DSLR or the CCD?

When you convert to JPEG and compress the image for WEB then adjacent pixels are averaged so it is not possible to look at your posted image and say for sure if it is a defective row, could only do this by looking at the uncompressed debayered image from a single sub (TIFF format is good).

William.

[Davey-T]

DSLR images, it's visible on single subs. seems to have suddenly appeared half way through an imaging session., I was imaging Comet Lovejoy with no sign of lines then had a quick go at the Rosette Nebula to see how the 60Da captured the red and the lines appear in those subs JPEG and CR2 .

Didn't take any flats will take some later when it cools down.

Dave

[lensman57]

Were you dithering?

A.G

[Davey-T]

Were you dithering?

A.G

Not in the sense you mean

Dave

[lensman57]

Not in the sense you mean

Dave

If it is on all the subs and in the same place then it maybe a dead row of pixels take an ordinary photo and see if the line is still there.

A.G

[Davey-T]

Done some tests today and it seems to be a USB cable problem, pic's in daylight saved on card are OK, pic's taken using Canon Util's and cable that came with the camera are OK.

Pic's taken with Canon Util's and 3 meter USB cable have the lines.

Should it work with 3 meter USB cable ? I'm sure I've done this before OK but may have been a different cable.

Dave

[steppenwolf]

A 3 metre cable for USB 2.0 *should* be fine BUT not all USB cables were created equally. With data cables, you tend to get what you pay for so an 'Ebay special' at low cost may well start to fail at this length. I'm pleased for you that it is the cable and not the camera though as this can be resolved with a higher quality cable (or maybe just a half reasonable replacement for the existing one which may have a fault). if you can get a solid connection without using an additional hub, that would be ideal.

[wxsatuser]

I have seen a line on odd occasions, it's more or less where yours is.

Not every image gets it and I cannot normally see it on individual subs.

Hard stretch seems to bring it out.

I don't use any cables, apart from the AC supply and a timer, images direct to card.

I have'nt tried to correlate this to temperature so not sure if it is that.

[Davey-T]

Thanks Steve, it was plugged directly into USB 2 on laptop, I think it's a Nikae ? cable from Maplin gold plated so probably cost £10.0 not cheap.

Never had it before or maybe not stretched the image as much, looked at a few old images and can't see it on them.

Dave

[steppenwolf]

I'd be tempted to borrow another 3m cable and try it - this could just be a duff plug connection if you haven't had the problem before.

[Davey-T]

Got a couple more somewhere, will dig them out and do some more tests.

Dave

[Oddsocks]

Could also be induced earth loop noise if you are using separate external power supplies for the laptop and camera, would be worse with longer USB cable, if you are using separate external PSU's for both then try running one or the other on internal battery only with the long cable and see if the line disappears.

[Davey-T]

Camera was on internal battery, can't remember if laptop was on battery or mains, but took some test shots with both on battery today and the line is still there with 3 meter cable.

Dave

[NickK]

Hmm - lines that are specific to an image in a straight row aren't normally a problem with usb.. but I normally look either power or possibly a sensor issue such as hot or non-flat response.. most of the time dithering or winsored stacking will take care of it.

[Davey-T]

Line is still there in stretched dark taken with USB cable.

Will do some to SDHC card later, just put camera out to cool.

Dave

90sec dark ISO800