Decoding a JPEG from a byte array

[David Robison]

I'm reading a JPEG image into a byte array (byte[]). What I need to do is to decode it, resize it, and then re-encode it. I'm new to opencv and javacv. Can someone point me to where I might find some simple code to do this? I am currently doing it with ImageIO but am having issues with JPEG decoding time and want to see if javacv does a better job at decoding the JPEG in less time. Thanks, David

[Samuel Audet]

There are a couple of methods for that in the opencv_imgcodecs module:
http://bytedeco.org/javacpp-presets/opencv/apidocs/org/bytedeco/javacpp/opencv_imgcodecs.html#imdecode-org.bytedeco.javacpp.opencv_core.Mat-int-

http://bytedeco.org/javacpp-presets/opencv/apidocs/org/bytedeco/javacpp/opencv_imgcodecs.html#imencode-java.lang.String-org.bytedeco.javacpp.opencv_core.Mat-org.bytedeco.javacpp.BytePointer-org.bytedeco.javacpp.IntPointer-

Let me know if you have issues using those!

Samuel

[David Robison]

Thanks, this helps. One thing I haven't figured out yet is how to take my JPEG that is in a byte array (byte[]) and create a Mat object that I can then send to the imdecode routine? David

[Samuel Audet]

Just call `new Mat(byte[])`, that will do what we need it to do.

Samuel

[David Robison]

Thanks. If there is an error in imdecode such that it returns mat::data == null, is there a way to retrieve what error was seen? David

[Samuel Audet]

It might return an exception, but not according to the docs:
http://docs.opencv.org/trunk/d4/da8/group__imgcodecs.html#ga26a67788faa58ade337f8d28ba0eb19e