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Isaac I. Ullah, PhD

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I’ve put together a small script to automate the process of creating a “super resolution” image from a series of handheld photos, and I thought I’d share it here. This basically emulates the “pixel shift” feature on certain Pentax and Olympus cameras by taking advantage of your shaky hands! The script, as well as much of the information below and some sample images you can use to test it out, have been merged into the pixels.us scripts github repo, under the directory “superres”. The main set of sample images can be found here

Why might you want to do this, you ask? Well, for a couple of reasons:

  1. You only have a low resolution camera on hand (your cell phone, for example), but you come across a scene that you want to record in high detail.
  2. You have a good camera, but you want MOAR MEGAPIXELS!!!
  3. Did I mention MOAR MEGAPIXELS!!!???

Some of the subsidiary benefits of this routine are:

  1. Reduction of image noise.
  2. Enhancement of details and apparent sharpness.
  3. Ability to recover relfectance details lost when shooting jpeg instead of RAW.

Applications in archaeology include:

  1. Creating enhanced resolution images of artifacts for archival purposes.
  2. Creating enhanced resolution images of stratigraphy, soils, or landscapes for later analysis.
  3. Geeking out in the computational archaeology lab on Friday afternoon.

Here’s the “readme” for the script, with basic usage instructions and some examples of what it can do. As always, feel free to contact me with questions or suggestions!


USAGE:

./SR.sh

DIRECTIONS:

Place this script into a directory containing a sequential series of “.jpg” images of the same scene. Images should be taken hand-held with any image stabilizion off, and with a fast shutter speed to avoid motion blur. They should have been taken in quick succession to avoid changes in lighting conditions or other movements in the scene. At least 8 or 10 images are needed, and probably no more than 20. Open a terminal in this directory and execute the script with ./SR.sh. It will create a new subdirectory for the aligned images, and will produce two output “super resolution” images with detail at twice the resolution of the input images. One, SR_mean.jpg uses the mean of the image stack to calculate the final pixel values (better luminosity values and potential increase in dynamic range. Chance of “ghosting”if images not perfectly aligned). The other, SR_median.jpg will use the median value (better sharpness, perhaps, and less chance of ghosting effects).

SAMPLE IMAGES:

I’ve included a small series of sample images so that you can test the script on your system, which can be found in the sample_images subdirectory. These are a series of 8 megapixel jpeg images shot with a Nexus 5x Android phone, handheld, using the awesome Open Camera app (FOSS!). The images are of my bookshelf here in my campus office, which offers enough detail to see the difference between the original 8 megapixel versions, and the ~32 megapixel result of the super resolution. You can use these images to experiment with the script, but here are some results using the default values (shown at a 400% crop):

——————— Orignal image ————————————— Superresolution ————————

Original 400% crop Superresolution 400% crop

HINTS:

  1. Ensure the script is executable with chmod 755.
  2. If you want the script to automatically remove the temporary resized or aligned versions of the images after the script is finished, you can uncomment the last line of the script: #rmdir -fr resized # remove interm images. otherwise you can manually delete the directory yourself.
  3. I chose default values for align_image_stack that seemed to work well with my test images. You may find that you need to alter some of the variables for best results with your own images. I suggest reading about align_image_stack here and here. In particular, you may need to adjust the number of control points (the number after the -c in the align_image_stack command)
  4. This technique is fairly computationally expensive, so it may take some time – especially on a slower computer or with large image files. Set it in motion, and then go make a sandwich while it process…

DEPENDS:

You must have imagemagick and hugin-tools installed. The script invokes convert from imagemagick to do the upscaling and image averaging, and align_image_stack from hugin-tools to align the hand held images. On *buntu distros, install them with apt: sudo apt-get install imagemagick hugin-tools or with your favorite package manager.