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26

Your exposures are very different. Ignore the quantity of images that you captured for a moment... and just compare the the single exposure settings (for reasons I'll describe in a moment). Top: 13 seconds at f/5 using ISO 1000 Bottom: 60 seconds at f/5.6 using ISO 6400 These are very different exposures. If you wanted the top photo to have an "...


21

That's a 'halftone pattern'. Halftones are a method of creating color separations for offset printing printing presses. This image was probably scanned from an offset printed piece. Offset printing presses don't really have the ability to print shading. Halftones use a series of dots of various sizes in a grid to give the illusion of gradation. In the ...


7

They don't. You're interpreting the raw data wrong. According to the PiCamera documentation, the Pi's 10-bit raw data is encoded as 5 bytes in the following manner: The Pi's Bayer array is BGGR. So the first four bytes contain the most significant bits (bits 10–3) of the blue, green1, green2, and red sensels, respectively. The fifth byte of data packs the ...


5

This is the nature of lossy JPEG compression. The compression process works by splitting an image into 8x8 pixel patches, and compressing each of them individually, with no concern for the boundary conditions where each patch joins with its neighbors. The theory is that very small details can be modified and/or discarded without our visual system taking too ...


5

Typically the software that creates the jpeg does some noise reduction. There are often options on the camera for how much to do. Software that works with raw photos usually has options for noise reduction, but starts out without any. You get to choose how much you do.


4

Some cameras have a 'long exposure noise reduction' setting which should eliminate hot pixels and reduce digital noise. Two exposures are taken in immediate succession, the first with the shutter open with your image in view, the second with the shutter closed. The latter will consist only of black, hot pixels and noise. This second exposure is 'subtracted', ...


3

The image is a bit "jpeggy", there is artefacting in the flat colour areas & at high contrast edges which a machine AI system might reject. Example of jpg artefacting at contrast edges The image size is also a bit small for a modern stock library; it's about 3mp compared to the 20mp or more that they might be expecting to see these days. I ...


3

Focus (both auto and manual) can be surprisingly complex and errors are more noticeable at short distances and narrow depth of fields. In addition to possible user error, there are a number of mechanical factors to be aware of. The one I want to concentrate on is Calibration. Focusing is performed on a sensor that is not the same as the main image sensor ...


3

Some possible reasons the focus distance in the image was closer to the camera than where the autofocus point used was superimposed on the scene at the time the image was taken: You locked focus and then recomposed. If you are using AF-S focus mode once focus is confirmed the camera will hold the focus at that distance as long as the shutter button is half ...


3

Using Darktable 3.2.1 I get this jpg with default settings. Then, I get this jpg with VNG4 demosaicing algorithm, default "sharpen" option and automatic exposure correction. I don't believe Darktable is to blame here. Maybe you are pushing too much some settings, since histogram shows an underexposed photo: Edit: Playing with 'L' in Lab color ...


3

The light source seems to be in the left of the image, close to the camera. Since all images were taken at night I belive it could be an insect very close to light source and camera. Like a moth or something like that.


3

Some links for you : Software : Try Deep Sky Stacker. It's freeware and designed for astrography. The site has some useful tips on technique and method as well, so read those even if you don't use the software. General purpose software : I do use Darktable for general photography processing, but it's not designed for astrography. For very tough RAW ...


3

Your premise is wrong and lies already in the definition of noise. if it would affect all sensor sites equally, it wouldn't be noise but only an offset. Noise means that some more-or-less random value is added to the signal, different for each sensor site. That's what makes it so hard to remove. see What is noise in a digital photograph? for an explanation ...


3

There is no way I can imagine that the same jpg can one day be 'clean' & another day be 'grainy', then the next back to 'clean', unless it is being viewed by an app that is failing to correctly load it, or is re-interpreting at load. The file itself is either good or it is broken. Broken files don't demonstrate 'grain' they either show large blocks of ...


2

I believe ISO 2000 is a bit high. I'd experiment with lower ISO, like 800. This is a good article explaining ISO in astrophoto. Also, 2.5 secs per picture is a bit low for an object like that. That's why you only get the bright core, but no arms. Can you expose more time, like 15 secs or more? Taking more frames will help you to increase signal-to-noise ...


2

By curiosity, I tried the state of the art denoiser BM3D [0] on the very first image from the OP; I used as parameters a putative white noise with variance of 0.0012, and find the result excellent: The color and luminance noise are gone and the fine structures of the clouds are revealed. [0] Mäkinen, Ymir, Lucio Azzari, and Alessandro Foi. "Exact ...


2

Given that sensor noise affects all sensor sites equally/randomly, why does the raw unprocessed Bayer data have such prominent vertical stripes? As @scottbb already explained the RAW format layout and why this creates the striped (in the chat session), you should know now that these are just low level "noisy bits" from four sensor sites (BGGR) combined into ...


2

This seems to be some insect that is drawn to the light. Due to the closeness to the camera, it is out of focus and appears that big.


2

This is the RAW image cropped but otherwise untouched, saved from Nikon's own ViewNX-i as a 100% quality jpg. It shows some hint of interference, as we're right down at pixel-peeping, but not the extra 'crunch' darktable seems to have added. The colour fringing is vastly reduced too. It has, of course, had the snot cropped out of it - it's down to 493x362 ...


2

It depends. Assuming both sensors have the same linear dimensions: If you are viewing the images from both sensors at the same display size, then the low light performance of both will be similar, assuming they use the same generation of technology. There are other advantages unrelated to low light S/N performance that make using a higher resolution sensor ...


2

Point lights are "hot pixels." Many image editing programs include a tool to remove them at the click of a button. There are some related questions questions and answers here. Long exposures are also subject to dark noise. There are some related questions and answers here.


2

JPEG compression artefacts. Choose a different compression setting, or export RAW.


2

Noise to signal ratio is poor at short exposures. You need them to be long enough and from what I remember before moving on to astrocameras, DSLRs are best when taking exposures at minimum 3.5 minutes. That pretty much means you need expensive tracking gear like a guidescope and guide camera. if you're just using a camera lens and mounted on top of a Star ...


2

Perhaps not a total fix, but some ideas in hopefully a helpful direction. I doubt the noise is camera noise at 100 or 200 ISO, if you are completely filling the frame of the D5000. My D5500 is newer, but I'm almost sure it couldn't be that much noisier than mine. It is, btw, just about fixable in Photoshop, pic at the end of a quick 'fix' attempt. To fix ...


2

Based on the comments on the question and some answers, I figured out the issue. The issue can be removed by enabling Match Greens: local average. If you also use AMaZE demosaic algorithm, the artifacts are completely gone:


1

This is the result of Lightroom, default settings +1 Exposure: Looks much more reasonable to me, with a little but of colour fringing which could be removed easily. Conclusion: the demosaicing algorithm of Darktable has trouble with the fine details in the feathers.


1

What you're seeing is colour moiré. Basically, you're paying the price of having a lens and sensor that can resolve the tiny detail of the weave of the fabric, but not quite the resolution needed to determine the colour because we use a Bayer-pattern colour filter to determine the colour. Note that the effect is only happening at a limited range of distances ...


1

These are dark images (cap on). With severe stripes it can be very noticeable on uniform lighting and sharp contrast transitions as well but it is most prominent in low light scenarios. The increase is likely caused by the buildup of heat in the sensor. The longer a sensor is energized, the warmer it will become and the noisier the output will be until the ...


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