How to apply codecs in LabView

[HovhannesAyvazovsky]

I have a stream of JPEG files (wireless transmission) and i need to compress them before sending and decompress after receiving. Using NI Vision toolkit namely IMAQ AVI2 Codec Names.vi I found out that I have codec H.264. How can i use it for compressing and decompressing JPEG files. Is it possible using NI Vision toolkit ?

Thank you in advance.

[GerdW]

Hi Hovhannes,

why do you want to compress and decompress JPEG files?

- JPEG already is compressed and has a certain datastructure: compressing it with "lossy" compression like H264 will damage that data structures!

- Have you tried to ZIP the files? (With JPEG files you will maybe gain 1-2% filesize…)

[HovhannesAyvazovsky]

Thanks for replay.

When I compress my images with JPEG converter (IMAQ Flatten Image to String.vi) for transfer it I get a very bad quality. Because of it i want to compress my data send in via serial port and decompress so as not to have a strong loss of quality.

[GerdW]

Hi Hov,

did you read the help and did you play with the parameters?

- You might change the quality of the JPEG compression.

- You might even switch off JPEG compression.

Did you try to ZIP the (image) string for transfer?

[HovhannesAyvazovsky]

Yes I know, but the file with appropriate size (for transfer minimum 15 frames per second) have very poor quality.

[Yamaeda]

It sounds like you basically need to reinvent MPEG. Don't send the full JPG, send the difference from the previous one.

/Y

[HovhannesAyvazovsky]

If it's not hard for you can tell how it can be implemented? I try to transfer video via UART with 230.4 kbit/s baud rate with minimum 15 frame per second. 

[GerdW]

Hi Hov,

I try to transfer video via UART with 230.4 kbit/s baud rate with minimum 15 frame per second. 

Wow.

Which frame size (in pixels)?

Some simple math: You can send ~23kB/s using your 230kbaud serial port. So you have just ~1.5kB/frame available: unless your frames are tiny the video quality will be poor…

[HovhannesAyvazovsky]

Frame size is 320x240

[GerdW]

Hi Hov,

Frame size is 320x240

So you are stuck with 1500byte/(320×240pixels)=0.02bits/pixel.

I'm not an expert with MPEG compression, but that sounds very low for me…