Transferring images¶
Intended audience: developers, Programming language: c++
Some optimized methods have been written to optimize image transfer between client and server using the attribute DevEncoded data type. All these methods have been merged in a class called EncodedAttribute. Within this class, you will find methods to:
- Encode an image in a compressed way (JPEG) for images coded on 8 (gray scale), 24 or 32 bits
- Encode a grey scale image coded on 8 or 16 bits
- Encode a color image coded on 24 bits
- Decode images coded on 8 or 16 bits (gray scale) and returned a 8 or bits grey scale image
- Decode color images transmitted using a compressed format (JPEG) and returns a 32 bits RGB image
The following code snippets are examples of how these methods have to be used in a server and in a client. On the server side, creates an instance of the EncodedAttribute class within your object
1 class MyDevice::Tango::Device_4Impl 2 { 3 ... 4 Tango::EncodedAttribute jpeg; 5 ... 6 }
In the code of your device, use an encoding method of the EncodedAttribute class
1 void MyDevice::read_Encoded_attr_image(Tango::Attribute &att) 2 { 3 .... 4 jpeg.encode_jpeg_gray8(imageData,256,256,50.0); 5 att.set_value(&jpeg); 6 }
Line 4: Image encoding. The size of the image is 256 by 256. Each pixel is coded using 8 bits. The encoding quality is defined to 50 in a scale of 0 - 100. imageData is the pointer to the image data (pointer to unsigned char)
Line 5: Set the value of the attribute using a Attribute::set_value() method.
On the client side, the code is the following (without exception management)
1 .... 2 DeviceAttribute da; 3 EncodedAttribute att; 4 int width,height; 5 unsigned char *gray8; 6 7 da = device.read_attribute("Encoded_attr_image"); 8 att.decode_gray8(&da,&width,&height,&gray8); 9 .... 10 delete [] gray8; 11 ...
The attribute named Encoded_attr_image is read at line7. The image is decoded at line 8 in a 8 bits gray scale format. The image data are stored in the buffer pointed to by gray8. The memory allocated by the image decoding at line 8 is returned to the system at line 10.