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Ghostscript:如何确定将多页PDF转换为多个TIFF的输出分辨率

分类: 技术问答 • 2022-05-02 17:43:18
问题描述：

我需要从扫描仪中提取一堆多页PDF文件中的TIFF图像. 在扫描过程中，我指定了600dpi的分辨率.

I need to extract TIFF images from a bunch of multi-page PDF files from a scanner. During the scanning I specified a resolution of 600dpi.

  1. 这是我用来生成TIFF图像的代码:

  1. Here is the code I used to generate TIFF images:

gs -q -dNOPAUSE -sDEVICE=tiffg4 \
   -sOutputFile=a_page%02d.tif a.pdf -r600x600 -c quit

这给了我正确数量的TIFF图像，但是，图像尺寸比我预期的要小.

This gave me the correct number of TIFF images, however, the image dimension is smaller than I expected.

无论我如何更改-r选项，输出图像都具有相同的大小.

No matter how I change the -r option, the output images have the same size.

这里发生了什么?

输出的TIFF图像具有一定的压缩率，如何更改gs选项，使其不包含任何压缩率?

The output TIFF images have some compression, how should I change the gs option so that they do NOT contain any compression?

http://pages.cs.wisc.edu /~ghost/doc/cvs/Devices.htm#TIFF 有几个选项可供选择，但在我看来，没有人表示"8位黑白" +无压缩".

http://pages.cs.wisc.edu/~ghost/doc/cvs/Devices.htm#TIFF has a few options to select, but seems to me no one means "8-bit Black&White" + "Compression Free".

有人解决这两个问题吗?

Does anybody how to solve these two problems?

答

如果使用tiffg4进行输出，则隐式要求在PDF中也获取Fax G4压缩类型.

If you use tiffg4 for output, then you implicitely asked to also get the Fax G4 compression type in the PDF.

您可以通过使用不同的TIFF输出设备(例如tiffgray(灰色，8位)，tiff24nc(RGB-TIFF，每个颜色通道为8位)，tiff32nc(CMYK)，告诉Ghostscript不使用压缩. -TIFF，每个颜色通道8bit)，....默认情况下，所有这些输出类型都是未压缩的.

You can tell Ghostscript to use no compression by using a different TIFF output device, such as tiffgray (gray, 8bit), tiff24nc (RGB-TIFF, 8bit for each color channel), tiff32nc (CMYK-TIFF, 8bit for each color channel), .... All these output types are uncompressed by default.

您也可以使用tiffg4，但是要删除压缩文件:

You can also use tiffg4 but remove the compression:

gs \
 -o a_page%02d.tif \
 -sDEVICE=tiffg4 \
 -r600x600 \
 -g4960x7020 \
 -sCompression=none \
  a.pdf

顺便说一句，没有"8bit Black + White"之类的东西.有"1bit Black + White"，但是一旦超出1bit，您将进入灰度级领域...:-)

BTW, there is no such thing as "8bit Black+White". There is "1bit Black+White", but as soon as you go beyond 1bit, you'll enter the realm of grayscales... :-)

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