HDRutils 0.9

Utility functions for performing basic operations on HDR images, including merging and deghosting

HDRutils

Some utility functions to generate HDR images from a sequence of exposure time or gain modulated images. You can find a separate Readme describing some functinos for noise simulations here.

Installation

To download HDRUtils, use Pypi via pip:

pip install HDRutils

If you prefer cloning this repository, install the dependencies using pip:

pip clone https://github.com/gfxdisp/HDRutils.git
cd HDRutils
pip install -e .

Additional dependency

You will need the FreeImage plugin for reading and writing OpenEXR images:

imageio_download_bin freeimage

Usage

Just import HDRutils and call the required functions

Reading and writing

Simple wrapper functions for imageio's imread and imwrite are provided to set appropriate flags for HDR data. You can even call imread on RAW file formats:

import HDRutils

raw_file = 'example_raw.arw'
img_RGB = HDRutils.imread(raw_file)

hdr_file = 'example.exr'
img = HDRutils.imread(raw_file)

HDRutils.imwrite('rgb.png', img_RGB)
HDRutils.imwrite('output_filename.exr', img)

Merge input images

The rawpy wrapper is used to read RAW images. Noise-aware merging is performed using the Poisson-noise optimal estimator. The generated HDR image is linearly related to the scene radiance

files = ['file1.dng', 'file2.dng', 'file3.dng']		# RAW input files
HDR_img = HDRutils.merge(files)
HDRutils.imwrite('merged.exr', HDR_img)

The default function processes each image individually using libraw and then merges the RGB images. This behaviour can be overriden to merge RAW bayer image by setting the flag demosaic_first=False.

Merge RAW bayer frames from non-RAW formats

If your camera provides RAW frames in a non-standard format, you can still merge them in the camera color-space without libraw processing

files = ['file1.png', 'file2.png', 'file3.png']     # PNG bayer input files
HDR_img = HDRutils.merge(files, demosaic_first=False, color_space='raw')
HDRutils.imwrite('merged.exr', HDR_img)

Alignment

While merging, some ghosting artifacts an be removed by setting HDRutils.merge(..., align=True). This attempts homography alignment and corrects camera motion for still scenes.

Estimate exposure times

The exposure times reported in EXIF camera metadata may be inaccurate. The merge function solves a linear least squares problem to estimate most suitable exposure times. This setting can be disabled by HDRutils.merge(..., estimate_exp=False). The default behaviour is to use the brightest 10% of the pixels for estimation.

Exposure estimation

Exposure metadata from EXIF may be inaccurate. The default behaviour is to estimate relative exposures directly from the image stack. If you are confident that metadata is correct, disable exposure estimation by specifying HDRutils.merge(..., estimate_exp=None).

For robustness, the estimation includes an iterative outlier removal procedure which may take a couple of minutes to converge especially for large images and deep stacks. You can override this by HDRutils.merge(..., outlier=None). For best results, supply the exact camera (instance of HDRutils.NormalNoise). Otherwise a default camera that works reasonably well for tested images will be used.

Citation

If you find this package useful, please cite

@inproceedings{hanji2020noise,
    author    = {Hanji, Param and Zhong, Fangcheng and Mantiuk, Rafa{\l} K.},
    title     = {Noise-Aware Merging of High Dynamic Range Image Stacks without Camera Calibration},
    booktitle = {Advances in Image Manipulation (ECCV workshop)},
    year      = {2020},
    publisher = {Springer},
    pages     = {376--391},
    url       = {http://www.cl.cam.ac.uk/research/rainbow/projects/noise-aware-merging/},
}