c# - 就地更新 PDF 图像
问题描述
我正在尝试使用PDFNet 7.0.4
和替换 SDF 文档中的图像流netcoreapp3.1
。我想尽可能地维护原始对象及其元数据;相同的尺寸、颜色系统、压缩等。理想情况下,对象数量甚至生成也将保持相同 - 目标是前后比较将仅显示流中更改的像素。
我Stream
使用这种方法将原始像素数据作为对象获取:
private Stream GetImageData(int objectNum)
{
var image = new PDF.Image(sdfDoc.GetObj(objectNum));
var bits = image.GetBitsPerComponent();
var channels = image.GetComponentNum();
var bytesPerChannel = bits / 8;
var height = image.GetImageHeight();
var width = image.GetImageWidth();
var data = image.GetImageData();
var len = height * width * channels * bytesPerChannel;
using (var reader = new pdftron.Filters.FilterReader(data))
{
var buffer = new byte[len];
reader.Read(buffer);
return new MemoryStream(buffer);
}
}
处理完图像数据后,我想在保存基础SDFDoc
对象之前对其进行更新。我尝试过使用以下方法:
private void SetImageData(int objectNum, Stream stream)
{
var image = new PDF.Image(sdfDoc.GetObj(objectNum));
var bits = image.GetBitsPerComponent();
var channels = image.GetComponentNum();
var bytesPerChannel = bits / 8;
var height = image.GetImageHeight();
var width = image.GetImageWidth();
var len = height * width * channels * bytesPerChannel;
if (stream.Length != len) { throw new DataMisalignedException("Stream length does not match expected image dimensions"); }
using (var ms = new MemoryStream())
using (var writer = new pdftron.Filters.FilterWriter(image.GetImageData()))
{
stream.CopyTo(ms);
writer.WriteBuffer(ms.ToArray());
}
}
这运行没有错误,但实际上似乎没有任何更新。我试过玩弄SDFObj.SetStreamData()
,但也无法完成这项工作。直接替换图像流中的原始像素数据的影响最小、性能最高的方法是什么?
编辑
我已经使用这种方法进行了一半:
private void SetImageData(int objectNum, Stream stream)
{
var sdfObj = sdfDoc.GetObj(objectNum);
var image = new PDF.Image(sdfObj);
var bits = image.GetBitsPerComponent();
var channels = image.GetComponentNum();
var bytesPerChannel = bits / 8;
var height = image.GetImageHeight();
var width = image.GetImageWidth();
var len = height * width * channels * bytesPerChannel;
if (stream.Length != len) { throw new DataMisalignedException("Stream length does not match expected image dimensions"); }
var buffer = new byte[len];
stream.Read(buffer, 0, len);
sdfObj.SetStreamData(buffer);
sdfObj.Erase("Filters");
}
这按预期工作,但有一个明显的警告,它只是忽略任何现有的压缩并将图像转换为原始未压缩流。
我已经尝试过sdfObj.SetStreamData(buffer, image.GetImageData());
,sdfObj.SetStreamData(buffer, image.GetImageData().GetAttachedFilter());
这确实更新了文件中的对象,但生成的图像无法渲染。
解决方案
以下代码显示了如何保留 Image 对象,但更改实际的流数据。
static private Stream GetImageData(Obj o)
{
var image = new pdftron.PDF.Image(o);
var bits = image.GetBitsPerComponent();
var channels = image.GetComponentNum();
var bytesPerChannel = bits / 8;
var height = image.GetImageHeight();
var width = image.GetImageWidth();
var data = image.GetImageData();
var len = height * width * channels * bytesPerChannel;
using (var reader = new pdftron.Filters.FilterReader(data))
{
var buffer = new byte[len];
reader.Read(buffer);
return new MemoryStream(buffer);
}
}
static private void SetImageData(PDFDoc doc, Obj o, Stream stream)
{
var image = new pdftron.PDF.Image(o);
var bits = image.GetBitsPerComponent();
var channels = image.GetComponentNum();
var bytesPerChannel = bits / 8;
var height = image.GetImageHeight();
var width = image.GetImageWidth();
var len = height * width * channels * bytesPerChannel;
if (stream.Length != len) { throw new DataMisalignedException("Stream length does not match expected image dimensions"); }
o.Erase("DecodeParms"); // Important: this won'be accurate after SetStreamData
// now we actually do the stream swap
o.SetStreamData((stream as MemoryStream).ToArray(), new FlateEncode(null));
}
static private void InvertPixels(Stream stream)
{
// This function is for DEMO purposes
// this code assumes 3 channel 8bit
long length = stream.Length;
long pixels = length / 3;
for(int p = 0; p < pixels; ++p)
{
int c1 = stream.ReadByte();
int c2 = stream.ReadByte();
int c3 = stream.ReadByte();
stream.Seek(-3, SeekOrigin.Current);
stream.WriteByte((byte)(255 - c1));
stream.WriteByte((byte)(255 - c2));
stream.WriteByte((byte)(255 - c3));
}
stream.Seek(0, SeekOrigin.Begin);
}
然后这里是要使用的示例代码。
static void Main(string[] args)
{
PDFNet.Initialize();
var x = new PDFDoc(@"2002.04610.pdf");
x.InitSecurityHandler();
var o = x.GetSDFDoc().GetObj(381);
Stream source = GetImageData(o);
InvertPixels(source);
SetImageData(x, o, source);
x.Save(@"2002.04610-MOD.pdf", SDFDoc.SaveOptions.e_remove_unused);
}
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