photo stacking

[thegunshow]

What is it all about and how do i use it to make my photos better?

[wulf]

It is used in macro photography (I've shuffled this thread across the the specific section) and is a way of overcoming depth of field restrictions by combining the sharp areas of multiple exposures.

Wulf

[daft_biker]

Originally Posted by thegunshow

What is it all about and how do i use it to make my photos better?

There are different kinds of "photo stacking".

For example some people used to sandwich slides together to view 2 pictures as one....maybe take a picture of a texture and overlay it over portrait or something. I doubt that's what you meant but it's there FYI anyway.

With digital there are a number of was of stacking images. In astrophotography exposure stacking is sometimes used - take several underexposed images of the same subject and then combine the exposures to make 1 correctly exposed image.

As with Wulf I suspect you meant focus stacking. In focus stacking you take several correctly exposed images of the same subject but move the focus between each shot. Later the shots are combined so you take the sharp bits of each shot to make 1 shot with much more in focus that can otherwise be achieved.

These are two different shots but hopefully close enough to illustrate the technique. The first shot is a single exposure of some fungi - the balls were about 1-2mm in diameter so this was shot at a fairly high magnification (about 4x lifesize at the sensor).

As you can see the DoF is very limited. This is due to shooting at such a high magnification even although I was using a tripod and could stop down as much as I like. At that magnification that's pretty much as much DoF as the laws of physics allow (while retaining good image quality!).

To get round that limitation I used a focus rail to move the focus between shots. The below image is a focus stack created from more than a dozen images like the above:


If you'd like to have a go at this technique you could try doing the stacking in software like CombineZM - it's free but I think it may be PC only. Good luck and have fun

[ressalg]

Stacking is also used in astrophotography. It's very common to use exposures of 5 mins or more (actually, 5 minutes would be considered rather short for astrophotography). In this situation it's used to combine exposures to bring out more detail. However, due to noise limitations of DSLRs usually exposures of 10 - 15 minutes are used. But, thanks to stacking, you can actually take (for example) three 10 minute exposures and combine them to achieve the same result as a 30 minute exposure. One of the biggest advantages is that it's not uncommon in very long exposures to get something going through the frame which might otherwise detract from the image (mostly airplanes and satellites leaving trails). Short exposures mean less chance of this happening. The program I use most often is Registax. But there are others: Deep Sky Stacker, Nebulosity and a few others I can't think of right now.

[kencaleno]

Combine ZM is a free downloadable focus stacking program; Helicon costs about US
$ 100
-Ken

[Jamesc359]

There's also another technique that is used to reduce noise. By taking five or six identical images and then overlaying them as layers with decreasing opacity in your image editing application you can all but eliminate noise.

The appropriate opacity should be 100 / layer number.

e.g.
Layer 6 - 16% (Topmost layer)
Layer 5 - 20%
Layer 4 - 25%
Layer 3 - 33%
Layer 2 - 50%
Layer 1 - 100% (Bottommost layer)

[kencaleno]

Originally Posted by Jamesc359

There's also another technique that is used to reduce noise. By taking five or six identical images and then overlaying them as layers with decreasing opacity in your image editing application you can all but eliminate noise.

The appropriate opacity should be 100 / layer number.

e.g.
Layer 6 - 16% (Topmost layer)
Layer 5 - 20%
Layer 4 - 25%
Layer 3 - 33%
Layer 2 - 50%
Layer 1 - 100% (Bottommost layer)

We are talking focus stacking here- but for noise you can go another 2 layers on what you have there,14% and 12% respectively-Ken

[ckodonne]

Originally Posted by Jamesc359

There's also another technique that is used to reduce noise. By taking five or six identical images and then overlaying them as layers with decreasing opacity in your image editing application you can all but eliminate noise.

The appropriate opacity should be 100 / layer number.

e.g.
Layer 6 - 16% (Topmost layer)
Layer 5 - 20%
Layer 4 - 25%
Layer 3 - 33%
Layer 2 - 50%
Layer 1 - 100% (Bottommost layer)

Quite brilliant...have to try that.

[inkista]

A third version of stacking, obviously, is enfuse's exposure-stack blending (i.e., an HDR/tonal-mapping-less approach to HDR.

It all depends on the math you're using to combine the bits you want from the member images in the stack. For noise, you're basically summing or average out all the information. For focus stacking you're looking to grab the sharpest bits (give precedence to contrast), and for enfusing, you're looking to establish and compress the full dynamic range of a scene.

Enfuse can be used for both focus stacking and HDR-like exposure stacking. It does, however, require that the images are already perfectly aligned, which is why you usually use it through a third-party GUI (like Hugin) that can also call auto-align (not sure, but I think the Lightroom plugin for Enfuse also does this. And there's EnfuseGUI). The biggest hurdle with focus stacking is making sure you've got enough coverage when you focus bracket.