code: public double getDefaultImageQuality(String mimeType) {
      if (StringUtils.isNotEmpty(mimeType)) {
        String format = StringUtils.substringAfter(mimeType.toLowerCase(), "image/");
        if (StringUtils.equals(format, "jpg") || StringUtils.equals(format, "jpeg")) {
          return DEFAULT_JPEG_QUALITY;
        }
        else if (StringUtils.equals(format, "gif")) {
          return 256d; // 256 colors
        }
      }
      // return quality "1" for all other mime types
      return 1d;
    }
docs: Get the default quality for images in this app generated with the Layer API.
  The meaning of the quality parameter for the different image formats is described in
  {@link com.day.image.Layer#write(String, double, java.io.OutputStream)}.
  @param mimeType MIME-type of the output format
  @return Quality factor