I began experimenting with a depth-of-field extension technique today called Focus Stacking. Analogous to HDR in some respects, this technique takes a set of images with overlapping zones of sharp focus and combines them into a single image exhibiting crisp focus throughout.
The first step is to take the set of images. Mount the camera on tripod, set the lens to Manual Focus and rack the lens out to be in focus on the nearest part of the picture and take that image. Then focus further away and take that image, continuing the process until you have the full set. The number of images will depend on the front-to-back distance, the lens focal length and the lens opening.
For landscapes, an iPhone calculator app is available called FocusStacker. You input your focal length and select the near and far distance and the calculator tells you the number of images, their focus distances and the lens f/stop.
Processing the Set of Images
I imported my image set into Lightroom 5 where I checked that the in-focus zone clearly progressed from front to back. At this point I could apply a series of LR adjustments, e.g., color balance, exposure, clarity, etc., but these should be synced across the set. Once done, I selected all the images in the set and followed the following steps for each of three different programs.
Since I already have Photoshop, I tried this first. The steps are:
- In Lightroom, select the images in the set and right-click.
- Click on “Open as Layers in Photoshop.”
- Photoshop will open and eventually show a single image containing a layer for each of the images in your set.
- Select all the layers.
- Edit | Auto-Align Layers | Auto.
- Edit | Auto-Blend Layers | Stack Images | Seamless Tones and Colors.
- Photoshop will calculate for a while and generate layer masks for each layer, selecting only the in-focus portions of each layer.
- If you find a spot where Photoshop allowed some out-of-focus area to show through, you can adjust the masks. Use a small brush with a high Hardness (80-90%) to do the adjustments.
- Crop the image to remove any edge alignment issues.
- Save the image. Remember if you use TIF with layers the image will be huge.
Here is a good YouTube tutorial: http://www.youtube.com/watch?v=DDpaKjA7RWI.
My initial feeling is that this was a very good way approach. It was pretty quick, used tools I already have and produced an impressively sharp image.
My next program was Helicon Focus, a program available on a free, 30-day trial basis, on their website. HeliconSoft offers several different specialized programs related to focus stacking, including Helicon Focus and Helicon Remote. I will discuss using the former.
I downloaded the trial version (it’s a dmg) and dragged it into the Applications folder. After assuring OSX that I really wanted to start it, it offered to install a plug-in in Lightroom. Doing so and restarting Lightroom allowed me to export images directly from Lightroom to Helicon Focus, which I then did.
The images were then listed with thumbnails in the Source Images panel of Helicon Focus, each with a checkmark indicating they were selected. Large views of individual images were available by clicking the image in the Source Images panel. I left the default settings on (and there is a button to restore the defaults if you need to) and clicked the Render button at the top right. Helicon Focus generated layer masks and then the image in short order.
The next step in the workflow is to go to the Retouching window which shows a split display, with a source image on the left and the final image on the right. The approach is to paint in a desired detail from a selected source image into the final image. This seems to work well.
The final step is to go to the Saving window, where you can save to disk, email, etc. in a variety of formats. The resultant image looked quite good and certainly the interface was quite easy to fathom.
The third program I tried was ZereneStacker, available as a free trial at their website, http://zerenesystems.com/cms/. Their website also has extensive tutorials and help files. Installing was quite easy and I quickly had it up and running. The first step was to export my image set from Lightroom as a group of TIFFs or JPEGs (I chose JPEGs). I dragged them from their export location into ZereneStacker’s Input Files sections. This is a left sidebar on a screen also containing two, side-by-side image browser windows. The left window shows the image selected in the Input Files section, while the right shows the finished stack.
Once there, click on Stack in the top menubar which shows three Align & Stack options, PMax, DMax or Both. There is extensive discussion of these options on their site but I picked DMax.
An image appeared in the right image browser window as it processed the stack. The program then asked me to set the contrast threshold (again, extensive discussion on their website). I stayed with the default. After some more processing, the output image was completed.
The final step is retouching, a process similar to those described above. When complete, the output image is ready to save. This is accomplished via File | Save As which allows choice of either JPEG or TIFF.
My test set was apparently very simple and led to output images from the three programs that were indistinguishable to me. For now, I will stick with Photoshop until my needs for the batching or more exotic controls of the other programs warrants spending for these undoubtedly fine applications.