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FOCUS-STACK() FOCUS-STACK()

NAME

focus-stack - Combine photos to create extended depth of field image

SYNOPSIS

focus-stack [options ...] file1.jpg file2.jpg ...

DESCRIPTION

focus-stack takes a set of photos taken at different focus settings and combines them into one, selecting the sharpest source image for each pixel position. This is commonly called extended depth of field, or focus stacking. Typical use is for microscope photography where it is difficult to obtain large enough depth of field to cover the whole subject.

Usually good results are obtained with the default settings, but following options are available:

Output file options

Set output filename. If file already exists, it will be overwritten. Format is decided by file extension. The formats currently supported by OpenCV are .bmp, .jpg, .jp2, .png, .webp, .ppm, .pfm, .sr, .tif, .exr and .hdr.
Generate depthmap image, which shows the depth layers determined from image stack. The brightness will be scaled from 0 to 255, where 0 is the first image given on command line and 255 is the last image.
--3dview=3dview.png
Based on depth map, generate a 3-dimensional preview image.
Save intermediate images from processing steps. This includes the aligned images and the final grayscale image before color reassignment.
Set the level of quality of the JPEG files (final and intermediates if asked to be written). The value can go from 0 to 100 with a default at 95.
Keep the full size of input images. By default images are cropped to the area that is valid for all images in the input stack, to avoid distortion near the edges.

Image alignment options

Select image index (starting from 0) to use as alignment reference. Images in a stack will usually vary in scale and position. All other images are resized and rotated to match with this image. This also determines the scale of the output image, which is important for performing measurements. By default middle image of the stack is used as reference.
By default each image is aligned against its neighbour. This improves results in deep stacks, as blur at the extreme focus levels can make direct alignment to reference inaccurate. However, if the images given as argument are not in correct order, or if some of them are of poorer quality, this option can be specified to align directly against the reference image.
By default the resolution of images used in alignment step is limited to 2048x2048 pixels. This improves performance, and because sub-pixel accuracy is used in computing the gradients, higher resolution rarely improves results. Specifying this option will force the use of full resolution images in alignment.
The application tries to compensate for any white balance differences between photos automatically. If camera white balance is set manually, this option can be specified to skip the unnecessary white balance adjustment.
If camera exposure is manually controlled, this option can be used to skip unnecessary exposure compensation.
Only align the image stack and exit. Useful for further processing of the aligned images with external tools.

Image merge options

Set the level of consistency filter applied to the depth map, in range 0 to 2. Higher level reduces artefacts and noise in output image, but can also result in removing small objects that appear against a textured background. By default the highest filter level 2 is used.
Set level of wavelet-based denoise filter applied to the result image. Because focus stacking selects the largest difference from source images, it has a tendency to increase noise. The denoising step reduces all wavelet values by this amount, which corresponds directly to pixel values. The default value of 1.0 removes noise that is on the order of +- 1 pixel value.

Depth map generation options

Minimum contrast in input image for accepting as data point for depth map building. Range 0-255, default 10.
Smoothing of depthmap in image plane. Value is radius in pixels.
Smoothing of depthmap in depth direction. Value is in 0-255 units.
Add alpha channel to depthmap and remove constant colored background. Threshold is positive for black background, negative for white background.
Reduce halo effects in depthmap near sharp contrast edges. Value is radius in pixels.
--3dviewpoint=x:y:z:zscale
Viewpoint used for the 3D preview. Specifies the x, y and z coordinates of the camera and the z scaling of the depthmap values.

Performance options

Set the number of parallel threads in use. By default uses the number of CPU cores detected plus one to feed possible GPU accelerator. Lower number of threads also reduces memory consumption.
Set the batch size for image merging. Larger values may give slightly better performance on machines with large amount of memory, while smaller values reduce memory usage. Currently default value is 8 and maximum value is 32.
By default OpenCL-based GPU acceleration is used if available. This option can be specified to disable it.
Wait for given time if any image files are missing. Specifying this option allows to start processing before all image files have been captured from camera.

Information options

Report each step as it begins and ends, and also the alignment parameters and other detailed information.
Show application version number.
Show OpenCV library build information.

EXAMPLES

Combine all images in current directory, and write output to output.jpg
Combine all images, giving detailed printout of steps and write output to stacked.png
Generate a JPEG with the maximum quality level.

GPU ACCELERATION

This application uses OpenCV library and its OpenCL acceleration interface. The GPU used for acceleration can be selected by environment variable OPENCV_OPENCL_DEVICE which takes a value such as Intel:GPU:0 See OpenCV documentation for details.

REFERENCES

The algorithm used for combining images is described in Complex Wavelets for Extended Depth-of-Field: A New Method for the Fusion of Multichannel Microscopy Images by B. Forster, D. Van De Ville, J. Berent, D. Sage and M. Unser.

REPORTING BUGS

Bugs can be reported at https://github.com/PetteriAimonen/focus-stack/issues

May 2022