Hi all,
I just found the solution for that problem. I forgot <ContrastEnhancement> tag along with <GammaValue>. So the correct style should be:
<ChannelSelection>
<GrayChannel>
<SourceChannelName>1</SourceChannelName>
<ContrastEnhancement>
<Normalize/>
</ContrastEnhancement>
</GrayChannel>
</ChannelSelection>
<ContrastEnhancement>
<GammaValue>1</GammaValue>
</ContrastEnhancement>
Thanks,
Tuan Son