WebGL's image is not very good

Origin image is fine, but it is not what I want after publishing to WebGL.
May I choose not to compress images?

Yep, just go to quality settings and make sure your webGL quality level texture size is full, and the import settings on your textures are set to truecolor for webGL.

Thank you very much for replying.
I did what you say, but it didn’t work…
Big images(above 256128) always have good quality even though I didn’t do anything, but small image(6464, attached below) is always not good enough only in webgl(is also good in Unity Editor).

Sorry for my poor English.

2217550--147590--QQ图片20150723174609.png