【作者】 刘浩学； 崔桂华； 黄敏； 武兵； 刘瑜；

【Author】 LIU Haoxue~1,CUI Guihua~2,HUANG Min~1,WU Bing~1 and LIU Yu~1 1 School of Printing and Packaging Engineering,Beijing Institute of Graphic Communication, Beijing,China 2 School of Physics & Electronic Information Engineering,Wenzhou University,Wenzhou,China

【机构】 北京印刷学院印刷与包装工程学院； 温州大学物理与电子信息工程学院；

【摘要】 用5幅ISO 400标准图像作为原始参考图像设计了一个阈值判断实验,用来检验彩色印刷图像的色差阈值。各参考图像的颜色用变换方程改变其明度、彩度和色调的颜色,其中明度和彩度用指数变换,色调用色调角位移变换,每个视觉属性都有20个变换等级。变换后的图像与原始参考图像组成测试图像对,图像对色差用平均CIELAB色差表示,色差分布为0~4CIELAB色差等级。将所有图像对按照色差大小和三个视觉属性排列成升序序列和降序序列,每个属性有21级(其中有一个无色差图像对),总共组成600个测试图像对(5图像*3属性*20等级*2序列)。实验在暗室中进行,图像观察在CPC-8n标准灯箱中进行,照明光源为D50,照明大约为12201x。照明/观察条件近似为0/45,观察距离约600mm。12名色觉正常观察者参加了该实验,每个观察者对每个图像序列找出刚好可以分辨出色差的颜色对(升序序列)或者找出刚好不能察觉出色差的图像对(降序序列),每个实验重复两次。实验共得到720个判断阈值。首先用实验得到的判断阈值进行累计概率的计算,然后将累计概率转换为Z-Score函数,则色差阈值就是对应Z-Score=0的CIELAB色差值。实验结果显示,5幅图像明度、彩度和色调的平均色差阈值为1,49,1.54和0.78 CTELAB色差单位,说明色调的阈值色差远小于明度和彩度的色差,而且表明阈值色差的大小与图像的内容有关。更多还原

【Abstract】 Five ISO 400 images were used as test images and a method of limits psychophysical experiment was designed to test color-difference threshold in printed images.The color appearance of each original image was modified by an exponential function for CIELAB lightness and chroma,an offset function for CIELAB hue at 20 steps for each attributes respectively.The modified images and their originals were paired to form the test image pairs. The mean color differences of image pairs,ranged from 0 to 4 CIELAB units,were calculated by CIELAB color-difference formula and nearly uniformly divided into 21 grades for each attributes. The test image pairs were assessed in a CPC-8n lighting booth.12 normal color vision observers took part in the experiment.The experimental results showed that the mean color-differences threshold for lightness,chroma and hue attributes were 1.49,1.53 and 0.78 CIELAB units showing the threshold for hue was apparently smaller than that of lightness and chroma,and the thresholds of different images were dependent on the image content or color distribution.更多还原