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pfshdrcalibrate

NAME

pfshdrcalibrate - Create an HDR image or calibrate a response curve from a set of differently exposed images supplied in PFS stream.

SYNOPSIS

pfshdrcalibrate [--response <type>] [--calibration <type>] [--gauss <val>] [--response-file <filename.m>] [--save-response <filename.m>] [--multiplier <val>] [--bpp <val>] [--luminance] [--samples <val>] [--help] [--verbose]

DESCRIPTION

Create an HDR image or calibrate a response curve from a set of differently exposed images supplied in PFS stream.

When used with 8bit images, luminance in the output HDR image corresponds to real world values in [cd/m^2] provided that hdrgen script contained correct information on exposure time, aperture and iso speed. Note that sometimes ISO speed indicated by camera does not correspond to standard (ISO-100 is in fact ISO-125).

The accuracy of absolute calibration has not been thoroughly tested with different camera models, however one can expect the relative measurement error below 8%. Use pfsabsolute in case of systematic error.

OPTIONS

--response <type>, -r <type>

Allows to choose from predefined response curves. This can be used either to apply this response or use it as an initialization for automatic self-calibration. Predefined response curves are: "linear", "gamma", "log". Default is "linear".

--calibration <type>, -c <type>

Type of automatic self-calibration method used for recovery of the response curve. Accepted types include: "none", "robertson", "mitsunaga". Default is "robertson". In case "none" is chosen, a predefined response will be used, without self-calibration. More infomation on the algorithms can be found in:

M.A. Robertson, S. Borman and R.L. Stevenson

Dynamic range improvement through multiple exposures

In: Proc. of International Conference on Image Processing 1999 (ICIP 99), pp 159-163 vol.3

and

T. Mitsunaga and S. K. Nayar

Radiometric Self Calibration

In: Proc on IEEE Conf. on Computer Vision and Pattern Recognition (CVPR'99). Volume 1, p. 1374

--gauss <val>, -g <val>

Sigma value for the Gaussian used as a weighting function. Applies to Robertson02 algorithm. Default value: 16.0f

--response-file <filename.m>, -f <filename.m>

Use response curve saved in the matlab format file. Turns off automatic self-calibration. Uses Robertson02 model to apply the response curve.

--save-response <filename.m>, -s <filename.m>

Saves the response curve calculated during automatic self-calibration stage in a matlab format file. Can be later reused for set of images captured with given camera. Also works fine for plotting with gnuplot.

--multiplier <val>, -m <val>

Input multiplier value. Can be used to manipulate the range of source exposures. Default value is 256 since LDR images are by default scaled to 0..1.

--bpp <val>, -b <val>

Number of bits per pixel in input data from the camera. Default value is 8.

--samples <val>, -p <val>

Number of sample pixels used in inverse response computations in Mitsunaga algorithm. Default is 50000.

--fix-saturated, -x

Use this option if you see black pixels in overexposed / saturated areas. The black pixels are visible if all exposures contain pixel values that are outside reliable range (are under- or over-exposed). This flag gives non-zero weight for the brightest and the darkest pixels, thus avoiding zero-weighted pixels. Note that the calculated luminance values for these pixels are not reliable.

--luminance, -Y

Recovery of response curve will be performed for luminance channel only.

--verbose

Print additional information during program execution.

--help

Print list of commandline options.

EXAMPLES

pfsinhdrgen sample.hdrgen | pfshdrcalibrate -v -s response.m

Recover the response curve from set of exposures defined in sample.hdrgen and save it to response.m file. To view the response curve, run gnuplot and write 'plot "response.m"'.

pfsinhdrgen sample.hdrgen | pfshdrcalibrate -x -f response.m | pfsview

Create an HDR image from exposures defined in sample.hdrgen using the response curve "response.m" and view it. Fix the problem with black values given to overexposed pixels.

pfsinhdrgen sample.hdrgen | pfshdrcalibrate | pfsview

Create an HDR image from exposures defined in sample.hdrgen using the default self-calibration method and view it.

pfsinhdrgen sample_dcraw.hdrgen | pfshdrcalibrate -b 16 -r linear -c none | pfsview

Given that the script sample_dcraw.hdrgen refers to camera RAW files (see pfsindcraw), this example will generate an HDR image assuming a linear response.

pfsinhdrgen sample.hdrgen | pfshdrcalibrate | pfsview

Create an HDR image from exposures defined in sample.hdrgen using the default self-calibration method and view it.

pfsinhdrgen sample.hdrgen | pfshdrcalibrate -c mitsunaga -samples 100000 | pfsglview

Create an HDR image from exposures defined in sample.hdrgen using the mitsunaga self-calibration method with 100000 samples and view it in pfsglview.

SEE ALSO

pfsinhdrgen(1) jpeg2hdrgen(1) pfsview(1) pfsindcraw(1) pfsabsolute(1) pfsglview(1)

BUGS

Please report bugs and comments on implementation to Grzegorz Krawczyk <gkrawczyk@users.sourceforge.net>.