frameLocates: Find the frame read start positions in a FLIR SEQ video file.

In gtatters/Thermimage: Thermal Image Analysis

Description

Using readBin function, find everywhere in file where the magic-byte/thermal resolution info is stored: i.e. 640x480, 320x240. These positions denote where the image frame data is found in the larger video file and will facilitate extraction of image save times and pixel information.

Usage

frameLocates(vidfile = "", w = 640, h = 480)

Arguments

vidfile	Filename or filepath (as character) of the thermal video. Should end in .seq or .fcf. Not tested comprehensively so it may only work for certain camera models and software packages.
w	Width resolution (pixels) of thermal camera. Can be found by using the flirsettings function.
h	Height resolution (pixels) of thermal camera.

Details

FLIR cameras have built-in radiometric video saving functions. FLIR software also has similar video, or time lapse, functionality. These files are typically stored as .seq or .fcf and encode information on the thermal imaging camera model, calibration, date/time, etc. These meta-tags can be extracted using system installed software (Exiftool).

This function makes use of the readBin function in the R base package, by loading a small portion of the file in raw(). It then searches through this data vector for the magic byte sequence in hexadecimal (0200wwwwhhhh) where wwww is the image width in little endian hexadecimal, and hhhh is the image height in little endian hexademical.

The actual start of all the magic byte locations is empirically determined by the repeating pattern of locations within the file.

Frame refers to the still frame that is to be extracted from the thermal video file.

The function returns a list, containing the 'header' start (h.start) position of each frame and the 'frame' start (f.start) where pixel data is stored in raw, binary format (at present, in 16-Bit integers).

h.start and f.start can be passed to other functions to extract the precise times of each frame (getTimes) and to extract the actual frame by frame data (getFrames).

The length of h.start and f.start should be the same. If these are blank, then the detection process has not worked and the filetype might not be supported by this function.

Warning: this is not tested on all samples of all video file types and may return errors for .fcf files.

Value

Returns a list, containing two vectors, h.start and f.start. These should be the same length.

h.start	A vector containing the byte read position start points in the file to extract header information from each frame. Typically passed to the getTimes function.
f.start	A vector containing the byte read position start points in the file to extract raw, binary pixel data from each frame. Typically passed to the getFrames function.

Note

Requires Exiftool be installed in order to automatically determine thermal image width and height. If you know the width and height in pixels, then the frame start locations can be determined.

For information on installing Exiftool, see http://www.sno.phy.queensu.ca/~phil/exiftool/

Author(s)

Glenn J Tattersall

References

1. http://www.sno.phy.queensu.ca/~phil/exiftool/ 2. http://www.sno.phy.queensu.ca/~phil/exiftool/TagNames/FLIR.html

See Also

getFrames, getTimes, readBin

Examples

x<-frameLocates(vidfile = system.file("extdata", "SampleSEQ.seq", package = "Thermimage"))
x$h.start
x$f.start

gtatters/Thermimage documentation built on Sept. 28, 2021, 2:02 p.m.