What is an Image Stack

[stormbind]

I see some talk on here about image stacks. I was wondering if someone was willing to explain what an image stack is and how to implement one.

 

[Overread]

Image stacking is when you take a series of images where you keep the shooting settings and lighting the same for each shot - but each shot you move the camera little closer to the subject. Thus in the end you get a series of shots where the whole subject has been covered in indevidual parts. You then use software which will stack the results ontop of each other and give you a final single image which has all the combined details in a single dispaly. The result is that you get a much increased depth of field in the single composite image - a depth of field not possible with regular macro shooting abilities. It also retains sharpness though the image and thus is superior to using ultra small apertures like f22 - where diffraction will cause softness to the image.

Thus this method relies upon a static subject and a stable camera setup - idealy a tripod with a focusing rail. Further its easier to keep the focus on manual and at a fixed setting (magnification) and just move the camera itself closer using the focusing rail.

Here is an example;

Flickr Photo Download: stack4
ok there are better ones out there I know but this one is mine

However it is a tricky art and one has to get the frames in the right order and also with overlap between each frame in depth of field - otherwise the program can create errors

http://farm3.static.flickr.com/2740/4291932412_67503214d1_o.jpg


For refrence I use Combine ZP for this stacking though there are other focus stacking software options out there. The bonuse for CombineZP is that it is freeware and so does not cost a thing.

 

[stormbind]

Overread,

Thanks for the information. That is wonderful information and the image that you referenced is the same one that sparked my intrest in image stacking. Would it be possible for you to post the series of images composing the stack and then the final "stacked" image? Also, do you mind explaining more about how the order in which you take the images matters?

Again excellent post and you are a source of inspiration for me :thumbup:

 

[Overread]

The order you take the images in does not really matter BUT the order you load them into the software does matter a lot. They have to go so that the depth of field moves back (or forward I don't think that way matters) in a clear and constant motion - having a single frame suddenly moving back a step will break the series and cause problems. That is why its preferable to take the shots in order so that using the software is easier (since often it can be hard to tell by eye which frame comes before or after).

As an example:

these are the two extemes that made up the image that you can see above. As you can see the depth of field of each shot is not enough to cover the whole area that is wanted - so these and the shots in the middle are combined to give the composite. Note that the frame around the outside will change as you focus closer and that means that you have to remember to keep a clear space around the subject so that when the shots are stacked there is some cut away space.

And for a complete single post here is the final version again

Note that when taking these kind of shots there are two things to bare in mind. Firstly its often good to focus on the eyes and get a good keeper shot in a single frame - since you can never garantee that the insect will sit still for the duration of the shoot. Secondly its always best to move in the smallest distances possible - more complete frames is far better than fewer less complete frames.

For a good set of cheap focusing rails (And the set I currently use) the ebay hongkong focusing rails or adorama focusing rails ( they appear to be the same design) are a very affordable setup. The manfrotto rails are no good (and costmore) whilst about the best on the market are novoflex, but they cost a heck of a lot.

 

[stormbind]

Awesome posts! Thanks a ton.

 

[molested_cow]

I know you wrote "move the camera closer", but won't that change how big the subject is in the composition?

I was thinking along the line of adjusting the focal point but keep the zoom the same.

 

[Overread]

Kind of but at macro distances remember that adjusting the focus will also change the magnification of the shot as well. In the end I have heard of macro shooters using both methods to good effect with stacking software so I suspect that it does not make too much difference which is used (within reason).

However I prefer to keep a fixed magnification (fixed focal point) and move the camera closer toward the subject. This essentially keeps the magnification the same but does move the frame location - so as I said you do need to keep the edges of the frame clear otherwise when you get the final shots they will be cutting into the subject

 

[USM IS]

Why my macro's sucked for depth of field compared to others I saw. "Now I see", said the blindman........Mike

 

[Overread]

Actually stacking is often not the most commonly used method. Whilst the results of a good stack are fantastic and achive a depth of field that is otherwise impossible (as well as a sharper and less noisy image over all which is great for really seeing the finer details) the method is very risky. A single missed or duff frame can prevent the set of images from stacking correctly and correcting such a problem can take a long time in editing.

The thing that one has to master is not just perfect depth of field control but perfect angling of that depth of field - eg take a look at Dalantech's work
No Cropping Zone
He specifically works with the MPE65mm macro for very high magnification work and does not use the image stacking method. Instead he perfects the angle of his shots so that the limited depth he does have is used to its fullest. This is not something that is easy to achive and nor is it something that you get in a single shot - often you might take a good number of shots, but only one will have that perfect point where the depth of field covers a significant part of the insect.

 

[TiaS]

I know you wrote "move the camera closer", but won't that change how big the subject is in the composition?

I am confused by this as well.

If I take 3 images, stepping closer to my subject each time and than stack them, wouldn't that look strange? They are 3 different images, some with more background and some with the subject taking up more of the photo. Also as I step closer the subject gets bigger. How would those stack into one tidy image?

 

[USM IS]

I just downloaded Apeture 3 and it has "stacking". And I'm frustrated with my crappy macro's. So here below is three photo's "stacked. And below I will show one not "stacked". i can sure tell the difference!......Mike

not stacked

 

[Overread]

I know you wrote "move the camera closer", but won't that change how big the subject is in the composition?

I am confused by this as well.

If I take 3 images, stepping closer to my subject each time and than stack them, wouldn't that look strange? They are 3 different images, some with more background and some with the subject taking up more of the photo. Also as I step closer the subject gets bigger. How would those stack into one tidy image?

The best thing to help get your head around it is to try
Installation and Maintenance
download and install the CombineZP package. There is a guide/tutorial window that opens when you start the program that should help guide you through its basic operation.

Also if you look up at the 3 moth shots I posted earlier you can see that whilst there is indeed a difference in the framing of the first two single frame shots the subject itself is still squarly within the frame in both examples. Then in the stacked shot the extra framing from the upper shot is lost (since there is no data from the closer framed shots to add to that area). As for areas being soft and then sharp idealy (if all works well) the software will pickup the sharp areas from one shot and use them, dumping/hiding the softer blurred data from other shots. I have noticed that sometimes this fails to work and chances are there are more refineries to this than I am aware of.


Also another thing I forgot to mention earlier - a bonus of this method is that you can use a wider aperture for your macro work. Instead of f13 you could word down at say f8 or f5.6 for each of the stacked shots. Provided that the depth of field overlaps between each frame and that you get enough shots to complete the stack as you desire. This gives the bonus of a further incrased background blur to the image (often a feature many desire to have in their work).

I have also seen other examples of image stacking - you can use it for landscape work and even other creative ideas (one member on the site took two frame - one of a wall with a window in it with the wall and window in focus and the second image was of the sight through the window being in focus - stacking the two together to get both in focus.

 

[Foxman]

Ok, so a really dumb follow up would be. If you can slid your macro shot forward to achieve these stunningly detailed images, why couldn't you take multiple shots of a subject at different consecutive focal lengths to achieve the same thing without it being macro.

In other words, I take a shot of a barn 10 times using various focal lengths. In theory I should be able to load those images in the order of the focal length and stack those images to produce greater detail in the subject.

Taking that a step farther, you could incorporate the image stitching and image stacking to achieve even more incredible and detailed shots....in theory. I am assuming I am understanding the process.

 

[Overread]

One might find it easier to stack if the focus is what is adjusted rather than the focal length - I say that because changing the focal length will adjust the appearance of the image. If its between say 200mm and 300mm chances are the angle of view won't be too difference - but between say 18 and 50mm the different shots would have a greatly different angle of view that might prevent image stacking.
Further you would still have to ensure that you took into account the loss of edge frame.

The other idea of combining focus stacking and image stitching is also a really good idea - one would have to make sure that the depth of field of each series of shots was in line with each other but otherwise yes if you had a solid shooting platform and the time to take such a series you could.

The downside though is time - in the insect world insects are always likley to fly off - whilst also you have to consider such factors as wind, lighting changes and other things that might lead to differences between frames. Each difference might cause a slight problem (lighting change) or a big problem (wind through trees would result in blurred tree details when stacking because no leaf would be in the same place twice)