Video Sequences
Sequences of images are handled in RAVL in a similar way to
sequences of any other kind of object. Details of how streams
work can be found in Ravl.OS.Sequence.
The differences between image sequences and other RAVL sequences are
- A variety of "standard" video formats are supported (see below). Where
the data has a distinctive header (e.g. JPEG), this is used to determine the
format; otherwise (e.g. the CIF family) the filename suffix is used.
- Where there is a mismatch between the pixel types in file and image (for
example when reading a CIF video file into ImageC<RGBValueC>), the
appropriate conversion is automatically done.
Here's a summary of currently supported formats. (For an exhaustive list
use the 'conv -lf' command.)
- sqcif Binary byte YUV420 images, 72 by 88
- qcif Binary byte YUV420 images, 144 by 176
- cif Binary byte YUV420 images, 288 by 352
- 4cif Binary byte YUV420 images, 576 by 704
- 16cif Binary byte YUV420 images, 1152 by 1408
- yuv Binary byte YUV images, 576 by 720
- syuv Binary byte YUV images, 576 by 720 one image to a file.
- rgb Binary byte RGB images, 242 by 360
- rgb2 Binary byte RGB images, 288 by 384
- frgb Binary byte RGB images, 484 by 720
- frgb2 Binary byte RGB images, 576 by 768
- jpeg The libjpeg libraries support the storage of a sequence of compressed images in a single file.
Note: In YUV420, the colour is sampled at half the resolution of the intensity in both dimensions.
Before you can do video IO there are a few things you have to do:
Following is a example of how to use this mechanism to read and
write a sequence of images.
Reading a sequence
DPIPortC<ImageC<IntT> > in;
if(!OpenISequence(in,"myfile.cif")) {
// Failed to open input file.
// Report an error...
}
ImageC<IntT> value;
while(in.Get(value)) { // Get next image, stop if none.
... Process your image...
}
Writting a sequence
DPOPortC<ImageC<IntT> > out;
if(!OpenOSequence(out,"myfile.cif")) {
// Failed to open output file.
// Report an error..
}
while(... more images to write ...) {
ImageC<IntT> image;
... Generate your images ....
out.Put(image);
}
Advanced classes:
Develop classes: