Hi all, I’ve put together a small script to automate the process of creating a “superresolution” image from a series of handheld photos. 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, but here is a basic before and after:
Original Image (one of sequence of ten shots)
Superresolution Image (mean blending)
Here’s the “readme” for the script.
This is a Linux shell script to create a ‘super resolution’ image from a stack of lower resolution images.
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 ------------------------
HINTS:
- Ensure the script is executable with
chmod 755. - 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. - I chose default values for
align_image_stackthat 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 aboutalign_image_stackhere and here. In particular, you may need to adjust the number of control points (the number after the-cin thealign_image_stackcommand) - This technique is fairly computationally expensive, so it may take some time. Set it in motion, and then go make a sandwich!
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.
. Distortion corrections will make a very big difference.
