Split LDR image set using capturing time #1843
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Description
This PR aims at splitting a set of raw LDR images into subsets using the capturing time in order to build as many HDR images as LDR image subsets.
That makes the splitting independent from the exposure pattern. The pattern is given by the set of image exposures when the LDR image set is sorted according to the alphabetic order.
Up to now, only monotonic patterns was supported. However, it appears that in some cases the middle exposure is delivered at the first position, followed by the darker images in the increasing order and by the brighter images also in the increasing order. For a set of 7 LDR images here is this pattern's exposures: 0, -3, -2, -1, 1, 2, 3. Currently, the HDR image is built without using the reference exposure which appears at the first position, focusing only on the monotonic part of the image set and considering the middle exposition as an outlier.
In this PR, the timestamp corresponding to the capturing date and time is added to the structure containing information about the exposure parameters and the LDR image set is sorted with respect to this timestamp. For that timestamp, second is the unit.
We consider as a parameter (non exposed), with a default value set to 2s, the maximum duration between two consecutive captures inside a group of LDR images corresponding to a single HDR image.
From the time sorted set of LDR images, All durations between two consecutive images are computed. and a histogram is built from them. From that histogram we compute the number Nlow of durations lower than or equal to the parameter value and the number Nhigh of durations higher than the parameter value.
At both extremities of the sorted image set, all single images separated with a higher duration than the one defined by the parameter are considered as outliers. Nout is the number of outliers.
The number of LDR groups is given by Ng = Nhigh + 1 - Nout if and only if Nlow % Ng = 0
In case of a reliable number of groups cannot be estimated by using the capturing time, the former method based on file naming and monotonic exposure pattern is applied as a fallback.
Features list
Implementation remarks
By setting to 2 seconds the parameter for the maximum duration between 2 consecutive images within a HDR burst, due to the rounding occurring at the timestamp creation, the maximum duration allowed is 2.5 seconds.