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I am looking to transfer pixel data from a server to an android program. On the server, the pixel data is in form RGBA, with one byte per color / transparency. Unfortunately on android the the corresponding pixel format is ARGB, meaning the alpha channel comes before the color data, instead of after, like it does on the server. I am worried that shuffling the RGBA data to ARGB format on the server will be too slow, and so I was hoping to find another way around that. The server is written in python by the way. I am capturing the screen data using the function presented here: Image.frombuffer with 16-bit image data. If there is a way to grab screen capture using this method (or some other) in ARGB format or even RGB_565 I would love to hear about that as well.

One trick I thought of to solve this problem was to use the isPreMultiplied flag on canvas.drawbitmap(int[], ...) and then send only the RGB bytes from the server. Then I could recompose the RGB bits into ints on the android device and send that to drawbitmap, ignoring the alpha channel entirely.

However, this leaves me with another problem. Ints are comprised of 4 bytes, and I have a sequence of 3 bytes in my byte[] array (the RGB values). I was using some of the solutions proposed here: byte array to Int Array to convert my byte[] to an int[] when I was transferring RGBA data. But now that it is just 3 byte sequences, I'm not sure how to quickly convert it to ints. I am hoping for close to real time image updating so I need a way to do this quickly. Any ideas?

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Trevor
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1 Answers1

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int rgbInt = byteArray[0] << 16 + byteArray[1] << 8 + byteArray[2];    
// not sure these are in the correct order, you may have to swap the indexes around.

You might also need to include 

+ 0xFF << 24

to set the alpha value to opaque.

Dale Wilson
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