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1、第三章 图像的阶调层次复制原理v 在图像印刷复制中，阶调和层次的再现是很关键的质量判定依据。v 阶调和层次来源于颜色差异第一节 阶调和层次的概念一、阶调和层次的含义阶调和层次都可以表述为图像的颜色明暗或深浅变化1、 阶调（Tone）:是指图像信息还原中，一个亮度均匀的面积的光学表现，它是由各个阶梯层次排列起来而组成的集合。它较侧重对图像整体状况的描述。2、阶调值（Tone value）是指阶调的量度。Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Cr
2、eated with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd.Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyrigh
3、t 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd.Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd.v3、层次（Gr
4、adation）：是指图像上从最亮到最暗部分的密度等级。它是组成阶调的基本单元。它侧重对明暗等级之间差别的大小进行描述。以上两幅图，那幅图的阶调范围大图1图2Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose
5、 Pty Ltd.Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd.请比较上面四幅同阶调范围的图片，判断那幅图所容纳的层次数多Evaluation only.Evaluation only.
6、 Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd.Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Create
7、d with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd.v二、阶调/层次的数值描述v1、光学密度描述图像的阶调层次可以用光学密度描述，光学密度的基本定义式如下：光学密度的定义以视觉实验为基础，对视觉而言，等差的亮度变化并不是视觉等差的，而亮度对数的等差变化大致上却是视觉等差的。Evaluation only.Evaluation only. Created with Aspose.Slides f
8、or .NET 3.5 Client Profile 5.2.0.0.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd.Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Created with Aspose.Slides for .NET
9、 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd.Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.Copyri
10、ght 2004-2011 Aspose Pty Ltd.Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd.v2、阶调/层次的色度描述及其与光学密度的关系在等差的密度变化下，人眼对亮调区域的
11、密度变化的敏感程度要高于对暗调区域密度的变化。Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd.第二节 图像阶调和层次的复制v一、阶调复制曲线v 指原稿图像阶调数值与印刷品阶调数值之间的对应
12、关系曲线。v 图像阶调值可以是光学密度D，色度值L，网点面积率等。v 在数字印前中，数字图像的阶调值常以所谓的“灰度值”表示。灰度值所代表的只是数字图像信号的灰度等级，当然，灰度值可以有不同的光度学或色度学意义。不同曲线再现效果：在复制工艺中，用阶调再现曲线表达了原稿和印刷复制品密度之间的关系。Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Created with Aspose.Slides for .NET 3.5 Client Profile 5
13、.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd.3.0ABCDE印刷密度原稿密度1.03.01.0A：亮调和暗调压缩，中间调拉伸B：亮调和暗调拉伸，中间调压缩C：中间调和亮调压缩，暗调拉伸D：中间调和亮调拉伸，暗调压缩E：骨架黑版阶调曲线Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Created with Aspose.Slides for
14、.NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd.v二、阶调的还原复制和压缩复制v 在图像复制中，如果原稿的阶调层次状况正常，人们自然会追求印刷品能够还原复制，要求：复制品上的阶调值和原稿上的阶调值完全相等。即：v D(印刷品)=D（原稿）v L（印刷品）=L（原稿）v 这种复制方式称为阶调层次的“理想复制”，理想复制经常受到实际条件的限制，Eg:（原稿）（印刷）v问题：如何将原稿呈现的阶调“压缩”到印刷复制能够再现的阶调范围内v解决方法：
15、 1、密度线性压缩复制v 2、采用色度空间L进行压缩控制Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd.第三节 图像的阶调分布与阶调层次处理v一、图像的阶调分布v 图像的阶调分布是指各明暗
16、等级在图像中所占的像素（面积）比例,可以通过统计图像各明暗等级所具备像素数（面积）而获得图像的阶调分布 。阶调分布、调整详见Photoshop操作Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd.
