在C#中将DPI值设置为Tiff图像 [英] Set DPI value to Tiff Image in C#

问题描述

我正在尝试通过代码在C#中设置TIFF图像的dpi值，但是在保存图像后以某种方式无法保留这些值.

I'm trying to set dpi value of a TIFF Image in C# through code but somehow the values are not persisted after saving the Image.

using (var image = new Bitmap(@"c:\newimage.tif"))
{
    uint[] uintArray = { 300, 1}; //Setting DPI as 300
    byte[] bothArray = ConvertUintArrayToByteArray(uintArray);
    PropertyItem item = image.PropertyItems.Where(p => p.Id == 0x11A).Single();
    var val = BitConverter.ToUInt32(item.Value, 0);
    Console.WriteLine(val);
    item.Id = 0x11A;
    item.Value = bothArray;
    item.Type = 5;
    item.Len = item.Value.Length;
    image.SetPropertyItem(item);
    image.Save(@"c:\newimage1.tif"); //Save image to new File
}

此代码有什么问题?任何帮助将不胜感激. TIFF文件标签定义

What is wrong with this code? Any kind of help would be appreciated. TIFF file tag definitions

推荐答案

同时设置属性值和位图分辨率，然后重新保存图像应会更改分辨率(适用于我的示例图像).我相信原始文件必须具有X和Y分辨率的标签，不确定如果.NET不存在，.NET是否会添加这些标签(必须进行测试).

Setting both the property value and the bitmap resolution and then resaving the image should change the resolution (It worked on my sample image). I believe the original file has to have the tags for X and Y resolution present, not sure if .NET will add those tags if not present (would have to test).

这是一个使用.NET读取和写入TIFF图像的X和Y分辨率的示例:

Here's an example of reading and writing the X and Y resolution a TIFF image using .NET:

int numerator, denominator;

using (Bitmap bmp = (Bitmap)Bitmap.FromFile(@"C:\input.tif"))
{
    // obtain the XResolution and YResolution TIFFTAG values
    PropertyItem piXRes = bmp.GetPropertyItem(282);
    PropertyItem piYRes = bmp.GetPropertyItem(283);

    // values are stored as a rational number - numerator/denominator pair
    numerator = BitConverter.ToInt32(piXRes.Value, 0);
    denominator = BitConverter.ToInt32(piXRes.Value, 4);
    float xRes = numerator / denominator;

    numerator = BitConverter.ToInt32(piYRes.Value, 0);
    denominator = BitConverter.ToInt32(piYRes.Value, 4);
    float yRes = numerator / denominator;

    // now set the values
    byte[] numeratorBytes = new byte[4];
    byte[] denominatorBytes = new byte[4];

    numeratorBytes = BitConverter.GetBytes(600); // specify resolution in numerator
    denominatorBytes = BitConverter.GetBytes(1);

    Array.Copy(numeratorBytes, 0, piXRes.Value, 0, 4); // set the XResolution value
    Array.Copy(denominatorBytes, 0, piXRes.Value, 4, 4);

    Array.Copy(numeratorBytes, 0, piYRes.Value, 0, 4); // set the YResolution value
    Array.Copy(denominatorBytes, 0, piYRes.Value, 4, 4);

    bmp.SetPropertyItem(piXRes); // finally set the image property resolution
    bmp.SetPropertyItem(piYRes);

    bmp.SetResolution(600, 600); // now set the bitmap resolution

    bmp.Save(@"C:\output.tif"); // save the image
}

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