Upload bytes or base64 string to s3 ruby sdk

I'm trying to upload an image to s3 using the ruby aws sdk. I'm able to upload the base64 string if I don't set the content_type. If I do set the content_type to image/png the upload is just the generic image thumbnail.

obj = #<Aws::S3::Object bucket_name="mybucket", key="test">

>> params[:file]
>> "data:image/png;base64,iVB...."

obj.put(body: params[:file], content_type: 'image/png', content_encoding: 'base64')

How can I upload a Base64 string to s3? I'm also open to uploading as bytes if that's more straight forward