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This is not about HDR, exposure fusion, or any kind of bracketing (exposure, focus, ISO, what have you).

There's an excellent iOS app called Cortex Camera that takes a couple of dozen photos in a burst and then merges them to produce a low-noise photo -- one that has so little noise that you would normally consider it beyond the iDevice's capability. This doesn't need a tripod.

Is there similar functionality in Lightroom or another app? I find that when I shoot low-light on my NEX, I prefer using a relatively low ISO (400 or less) with a tripod. I was wondering if I could skip the tripod and instead take a burst of a couple of dozen photos, and then merge them in software?

EDIT: Based on the comments below, some clarifications are due:

  1. I don't have Photoshop. I do have Lightroom, so LR plugins are okay, as is standalone software.

  2. I use a Mac, so Windows software doesn't work for me.

  3. I don't want to use command-line tools.

  4. I'm okay with both free stuff ($0) and cheap software (like $20, not like $100).

  5. I am not looking for an onerous, multi-step process with multiple decisions to make and different things to try, but more like a 20-second one: drag the source images in, press Fuse, and press Save.

  6. I require the software to work without a tripod or a remote shutter release, since if I have to carry these with me, I might as well use a long exposure and be done with it.

  7. This means that the software should handle the camera moving a bit between shots (both horizontally and vertically) and rotating a tiny bit. It can't assume perfectly aligned shots -- that's not useful for me.

Kartick Vaddadi
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3 Answers3

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The technique used by Cortex Camera is called Median Blending. Astrophotographers have been using this concept for years to combine multiple photos of dim objects in the night sky to reduce the noise and increase contrast and color. It is often referred to as image stacking in which hundreds of images of the same piece of sky are overlaid and the values for each pixel are set at the median value for that pixel from all of the combined images. But astrophotography is far from the only type of imaging that benefits from Median Blending.

Most full featured imaging applications, such as Photoshop and the GIMP, include the ability to do image stacking. There are also some cameras such as the Sony A-mount and E-mount cameras that can do this in-camera. Depending on exactly which model NEX you have, your camera may already include this feature. It is called Twilight Handheld Mode. The camera captures a series of photos in rapid succession (maybe 5 photos) and then merges them to create a low-noise JPEG. As with anything done in-camera, you give up the finer control of a post-processing application for the convenience and time savings of letting the camera make many decisions for you.

Although it works fairly well without a tripod, for the ultimate in resolution you will still want to stabilize the camera. When the camera moves slightly from one frame to the next, then everything in the image will shift a certain number of pixels. If the shift is purely horizontal and/or vertical, there isn't much loss in terms of absolute resolution. This is rarely the case. When the shift from one photo to the next is diagonal, or worse yet rotational, then there is not a one-to-one correspondence of pixels from one frame to the next. The use of a Bayer filter to mask different pixels with different colors also comes into play when the camera shifts between exposure. This reduces the effectiveness of using the median value of each pixel by a miniscule amount in much the same way that using a lens correction profile to correct the distortion created by a lens' design will reduce the absolute resolution of an image.

Here are some links to articles and discussions on the subject:
http://petapixel.com/2013/05/29/a-look-at-reducing-noise-in-photographs-using-median-blending/
An expanded version of the same article:
http://blog.patdavid.net/2013/05/noise-removal-in-photos-with-median_6.html
http://www.digitalphotopro.com/technique/revolution/reduce-noise-with-multiple-shots.html
http://diglloyd.com/articles/LensAndCameraIssues/NoiseAndMultipleExposures.html
http://www.cambridgeincolour.com/tutorials/image-averaging-noise.htm
http://photography-on-the.net/forum/showthread.php?t=1221282

Michael C
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  • Thanks, Michael. Most of these articles seem to describe how to do this in Photoshop (which I don't have), or describe the general technique, which I already know (but I didn't know the term "median blending" -- thanks). But what software would you recommend? LR/Enfuse? – Kartick Vaddadi Nov 26 '13 at 06:08
  • BTW, I also need the software to compensate for diagonal displacement and rotation. If I have to use a tripod, I might as well use a longer exposure -- I won't need median blending / image stacking in that case. – Kartick Vaddadi Nov 26 '13 at 06:09
  • Multiple short exposures using median blending will be much less noisy than a single long exposure, even though you need a tripod for both. Read the diglloyd.com article for why the pixel displacement reduces overall image quality both in terms of noise and resolution. – Michael C Nov 26 '13 at 06:55
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    The first link lists three open source programs that may be useful to you. The open source GIMP has the ability to do image stacking. Additionally, http://deepskystacker.free.fr/english/index.html is free but the GUI is definitely intended for stacking very large numbers of dark sky images. Image stacker (http://www.tawbaware.com/imgstack.htm) is feature limited unless you register it for $17US. – Michael C Nov 26 '13 at 07:13
  • Thanks — I'll try GIMP if LR/Enfuse doesn't work for me. I'm surprised that even pro-level software like Lightroom or its plugins don't compensate for diagonal motion and rotation, when even $0.99 iPhone apps do. In any case, short of using a remote shutter release, I'm wary of taking multiple exposures, since I have to hold the shutter button down, which introduces shake. Whereas I can set a single long exposure with a 2-second timer and get a shake-free photo. Is that correct? – Kartick Vaddadi Nov 26 '13 at 09:48
  • BTW, regarding your comment that the diglloyd.com article says that multiple short exposures are better than one long exposure, I don't know if that article was comparing multiple short exposures to one short exposure or to one long exposure. It was not clear. Do you know any other sources for me to read up on this? Thanks. – Kartick Vaddadi Nov 26 '13 at 09:50
  • Sorry for the confusion. The first half of that comment is not in reference to the diglloyd article, the second half is. Comments condense spaces between paragraphs when posted here. – Michael C Nov 26 '13 at 10:33
  • LR is not meant to be a multiple image tool. It is intended to do one thing very well: convert individual RAW image files to a viewable image and allow those images to be organized. – Michael C Nov 26 '13 at 10:35
  • If you are serious about shooting in low light you need both a tripod and remote shutter release that doesn't require you to touch the camera between exposures. It is much simpler and affordable (in terms of time investment if not in terms of software) to use a tripod and remote release, and those things yield better results. – Michael C Nov 26 '13 at 10:40
  • In general multiple short exposures will not be "much less noisy" than a single long exposure, they might be slightly less noisy when exposure times go above a certain limit. Pixel displacement is not the problem Lloyd makes it out to be provided your stacker understands and can perform image alignment. Pixel displacement can even improve resolution if the stacker is smart enough. – Matt Grum Nov 26 '13 at 10:42
  • There are situations where use of a tripod is impractical or simply not allowed. Shooting a series of short handheld exposures at high ISO and then merging is a perfectly valid and very effective technique for reducing noise. However I don't know which free software can handle the alignment of images. – Matt Grum Nov 26 '13 at 10:45
  • Pixel displacement removes the absolute 1:1 correspondence of the same pixel position from one frame to the next, which is the entire basis for Median Blending. paragraph break As always it depends on the source of the noise: random shot noise or grid/read noise and hot pixels. Median blending is very effective for the first type and does nothing for the second type. – Michael C Nov 26 '13 at 10:48
  • "Do you know any other sources for me to read up on this? Thanks." There are over 47M results from the following google search: https://www.google.com/#q=noise+reduction+using+multiple+images+exposed+the+same. – Michael C Nov 26 '13 at 10:52
  • Yes, there are situations where a tripod is not allowed or not practical (and I also agree with the rest of your comment). But from the original question and the comments from the user who asked it, it seems to me that in this case the tripod and cable release are being avoided because they are considered a greater inconvenience than shooting handheld and then trying to align the images using free software. I think the second option is the more inconvenient one. – Michael C Nov 26 '13 at 11:00
  • I updated the question with clarifications. Please take a look. – Kartick Vaddadi Nov 26 '13 at 14:41
  • Median blending vs long exposures are a different question, because there we're assuming a tripod, but this question specifically avoids depending on a tripod. So, I split the other question here: http://photo.stackexchange.com/questions/45426/does-median-blending-image-stacking-result-in-better-or-worse-results-than-a-l Thanks. – Kartick Vaddadi Nov 26 '13 at 15:07
  • Gentle ping. Am I correct in understanding that there's no software that meets my criteria as listed in the modified question?paragraph break In any case, I can't figure out how to align photos in GIMP. I loaded a dozen or so photos as layers, but when I choose the Align Visible Layers command, the layers are not still aligned, as I can see using the Difference blending mode. I tried using all three styles — Collect, Fill and Snap to Grid — for both the horizontal and vertical options, but the photos are still not aligned. How do I get GIMP to automatically align layers? – Kartick Vaddadi Nov 29 '13 at 06:32
  • Pixel displacement is not a problem provided you measure it and take it into account during stacking (using interpolation) and the amount of parallax is negligible (I wouldn't recommend macro stacking with any sort of camera movement). Pixel displacement is the basis for multiple image super-resolution using the extra samples that are in between the pixels of your base image to resolve extra detail. – Matt Grum Dec 02 '13 at 10:01
  • @KartickVaddadi I assume the GIMP align layers tool simply aligns based on the size of the layer like earlier version of photoshop. What you actually want to do is called image registration, plugins exist for GIMP: http://registry.gimp.org/node/24248 to applying the median filter to your stack I believe can be done with G-mic http://registry.gimp.org/node/13469 though it might involve a little bit of scripting... this one might be easier: http://registry.gimp.org/node/2352 – Matt Grum Dec 02 '13 at 10:09
  • @MattGrum The reason for advantages in terms of resolution when doing typical stacking would actually be a hindrance when doing median blending because of the way median blending throws away the atypical results for each pixel in a series of images and uses only the values that are very near each other from one image to the next when determining each pixel's value in the output image. That is why median blending doesn't work well for astrophotography unless the camera platform is precisely tracking the sky. As the stars move from pixel to pixel they are seen as noise and filtered out. – Michael C Dec 02 '13 at 10:37
  • Not to mention that most cameras used in serious astrophotography are monochromatic and do not have a Bayer type filter. Instead the entire sensor is filtered for each wavelength in successive shots. – Michael C Dec 02 '13 at 10:43
  • Just to post a link that you can add to your answer... there is a nice tutorial here: http://blog.patdavid.net/2013/05/noise-removal-in-photos-with-median_6.html – Rmano Dec 03 '13 at 04:49
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    @Rmano That's the same basic article that was presented in the petapixel link in my answer. When I saw it while writing the answer I didn't realize how much additional material was in this one compared to the other. I think I'll add it as well. Thanks! – Michael C Dec 03 '13 at 15:44
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There is a way to do this in Photoshop (I'm using CS5 Extended)

  1. Shoot multiple exposures.

  2. In Photoshop, go to File > Scripts > Load Files into Stack.

  3. Click Browse and select the exposures to be used in the Stack and check Attempt to Automatically Align Source Images and Create Smart Object after Loading Layers. This will create a single Smart Object from the multiple exposures. Double-clicking on this Smart Object will allow you to see the layers separately.

  4. Go to Layer > Smart Objects > Image Stack Mode > Median to blend the separate exposures. You’ll see that the noise is reduced substantially.

  5. Optionally, compare Image Stack Mode > Mean. This works best for exposures containing no movement. (aka on a tripod)

Linuxmint
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Yes. Averaging exposures is similar to what you'll see in movies. If you stop on one frame, the grain is visible and often dust spots and scratches. When you're viewing at 24FPS, those aren't as noticeable because the subject is constant, but the grain has a randomness to it.

dtphoto
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