Thx a lot! My code is based on the custom shader sample, and I found the code:

Texture.defaultTo4bpp(true);

Change it to:

Texture.defaultTo4bpp(false);

and problem solved!

I'm doing basic normal map shading, but the result is quite strange.
So I attached the normal map directly to my model as the basic color and found it unexpectedly got compressed.
You can see the image bad.png in the attachment. The color seems sudden change and not smooth.
But the original texture is quite smooth as you can see the image good.png in the attachment.

Is there a way to avoid texture compression?
I already did:
normalTexture.setTextureCompression(false);
but not work.