Commit 4664fc0b authored by Philippe Renon's avatar Philippe Renon Committed by Nicolas Dufresne

opencv: add opencv image format documentation

https://bugzilla.gnome.org/show_bug.cgi?id=774576
parent f6021e00
......@@ -26,6 +26,55 @@
#include "gstopencvutils.h"
#include <opencv2/core/core_c.h>
/*
The various opencv image containers or headers store the following information:
- number of channels (usually 1, 3 or 4)
- depth (8, 16, 32, 64...); all channels have the same depth.
The channel layout (BGR vs RGB) is not stored...
This gives us the following list of supported image formats:
CV_8UC1, CV_8UC2, CV_8UC3, CV_8UC4
CV_8SC1, CV_8SC2, CV_8SC3, CV_8SC4
CV_16UC1, CV_16UC2, CV_16UC3, CV_16UC4
CV_16SC1, CV_16SC2, CV_16SC3, CV_16SC4
CV_32SC1, CV_32SC2, CV_32SC3, CV_32SC4
CV_32FC1, CV_32FC2, CV_32FC3, CV_32FC4
CV_64FC1, CV_64FC2, CV_64FC3, CV_64FC4
Where the first part of the format name is the depth followed by a digit
representing the number of channels.
Note that opencv supports more that 4 channels.
The opencv algorithms don't all support all the image types.
For example findChessboardCorners() supports only 8 bits formats
(gray scale and color).
And, typically, this algorithm will convert the image to gray scale before
proceeding. It will do so with something like this:
cvtColor(srcImg, destImg, CV_BGR2GRAY);
The conversion will work on any BGR format (BGR, BGRA, BGRx).
The extra channel(s) will be ignored.
It will also produce a result for any RGB format.
The result will be "wrong" to the human eye and might affect some algorithms
(not findChessboardCorners() afaik...).
This is due to how RGB gets converted to gray where each color has a
different weight.
Another example is the 2D rendering API.
It work with RGB but the colors will be wrong.
Likewise other layouts like xBGR and ABGR formats will probably misbehave
with most algorithms.
The bad thing is that it is not possible to change the "default" BGR format.
Safest is to not assume that RGB will work and always convert to BGR.
That said, the current opencv gstreamer elements all accept BGR and RGB caps !
Some have restrictions but if a format is supported then both BGR and RGB
layouts will be supported.
*/
gboolean
gst_opencv_parse_iplimage_params_from_caps (GstCaps * caps, gint * width,
gint * height, gint * ipldepth, gint * channels, GError ** err)
......
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