Meaning of CNN filters

I thought CNN's filters are determined. but it is not!

When I construct CNN layers with the filter size(for instance 64, 32 and so on), I thought filter's weights were determined by CNN author and just use it but it wasn't!

Basically Conv Filter's weights are also trainable. To verify this is really easy.

1. Construct CNN layers without train.
2. Visualize all the images with filter applied.

and then compare it with

1. Construct CNN layers with train.
2. Visualize all the images with filter applied.