Fixed: related x_resolution, y_resolution
  Fixed: test_density(Image_Attributes_UT) in Image_attributes.rb fails #76
  Fixed: test_x_resolution(Image_Attributes_UT) in Image_attributes.rb fails #81
  Fixed: test_y_resolution(Image_Attributes_UT) in Image_attributes.rb fails #82
Fixed: removed tests for the default value
Merge pull request #102 from u338steven/patch-6

Fixed: related x_resolution, y_resolution