标准图象 meaning in English

reference image

Iron and steel . methods of determination of content of non metallic inclusions in wrought steel . part ii : micrographic method using standards diagrams
钢铁.锻钢中非金属杂质含量的测定方法.第2部分:标准图象显微照像法
Iron and steel . characterization of sulfide shapes in structural steels with improved machinability using standard diagrams . micrographic method
钢铁.用标准图象确定改进机械加工性能的结构钢硫化物形状的特征.显微照相法