in optical reading systems(OMR,OCR),the recording surface(paper) considered with respect to its contrast to the characters or marks to be read

• 在光学输入系统（例如光标志阅读器，光代码读出器）中，指从与准备原阅读的光（字）符或光标志形成的反差出发考虑的记录表面的状况