使用Ghostscript生成缩略图可旋转风景pdf页面的设备尺寸定义 [英] Thumbnail generation with Ghostscript rotates my device size definition for landscape pdf pages

问题描述

我想使用GS从pdf文件生成缩略图.

• 缩略图必须适合90x120像素的矩形
• 图像不应旋转
• 应调整图像的大小以适合矩形并保持宽高比

我使用以下命令:

gswin32 -dPDFFitPage -dPARANOIDSAFER -dBATCH -dNOPAUSE -dNOPROMPT 
-dMaxBitmap=500000000 -dAlignToPixels=0 -dGridFitTT=0 
-dDEVICEWIDTH=90 -dDEVICEHEIGHT=120 -dORIENT1=true 
-sDEVICE=jpeg  -dTextAlphaBits=4 -dGraphicsAlphaBits=4 
-sOutputFile=output.%d.jpg input.pdf

结果:

如果我在人像页面上使用某些PDF 像此示例，您可以下载该缩略图，然后缩略图正确无误，如您在此处看到的那样:

如果我将其用于具有风景页面的PDF ，则设备宽度为作为高度:

如何防止这种行为?我也希望我的保时捷也能达到90x120.我想也许我需要为Ghostscript提供一些Postscript代码(带有-c命令行参数)，但是我对此没有经验.有人可以帮我吗?

EDIT1 : 我尝试了 KenS的建议.有了-dFIXEDMEDIA，我的保时捷就会像下面看到的那样被裁剪:

EDIT2 :对于肖像图像，Kurt Pfeifle的第一个解决方案不可行(白色部分)右侧，未正确使用空间).见下文:

EDIT3 : Kurt Pfeifle的第三种解决方案几乎是不错的选择.对于风景图像，它是完美的:

但是，纵向页面存在尺寸调整问题，并且背景也完全变为灰色:

所以，库尔特，我想我可以将pdf分成页面(使用GS -dFirstPage和-dLastPage)，然后，如果您有什么想法，请如何确定页面是否为风景或肖像，那么我可以进行一些条件处理.任何的想法?至于背景颜色，我认为它并不重要，但是如果您在这里也有想法，那么欢迎他们.

解决方案

好吧，现在基于上述 '首先处理PDF的思想(以便它使用纵向媒体格式以显示其横向图像内容)' ...

请注意，由于您的原始PDF并非在所有页面上都使用相同的大小(它们都不同)，所以我仅在第一页上做过概念验证.

步骤1:从原始图片(景观)中提取第1页

我为此使用pdftk:

porsches.pdf  cat 1  output porsche-page1.pdf

第2步:在较大的肖像页面上将风景内容居中

我正在为此使用Ghostscript以及-c ... PostScript命令行片段:

gs \
 -o porsche-page1-on-portrait-medium.pdf \
 -sDEVICE=pdfwrite \
 -dPDFSETTINGS=/prepress \
 -g1920x2560 \
 -r72 \
 -c "<</PageOffset [0 560]>> setpagedevice" \
 -f porsche-page1.pdf

/PageOffset值源自以下事实:我在原始页面高度1440点上添加了1120点.因此，我将内容向上移动一半，以使图片再次居中.

第3步:创建JPEG缩略图(人像)

gs \
 -sOutputFile=proofofconcept-thumb_%03d.jpg \
 -dPDFFitPage \
 -dDEVICEWIDTH=90 \
 -dDEVICEHEIGHT=120 \
 -sDEVICE=jpeg \
  porsche-page1-on-portrait-medium.pdf

除非我没有完全误解您的意图:这应该是您想要的结果. (注意:我在缩略图上添加了黑框，以使它的真实尺寸可见，即使在Stackoverflow的白色HTML背景上也是如此.

I want to use GS to generate thumbnails from pdf files.

• The thumbnail must fit a 90x120 pixel rectangle
• The image should not be rotated
• The image should be resized to fit the rectangle with keeping aspect ratio

I use the following command:

gswin32 -dPDFFitPage -dPARANOIDSAFER -dBATCH -dNOPAUSE -dNOPROMPT 
-dMaxBitmap=500000000 -dAlignToPixels=0 -dGridFitTT=0 
-dDEVICEWIDTH=90 -dDEVICEHEIGHT=120 -dORIENT1=true 
-sDEVICE=jpeg  -dTextAlphaBits=4 -dGraphicsAlphaBits=4 
-sOutputFile=output.%d.jpg input.pdf

Result:

If I use some PDF with portrait pages like this example, which you can download, then the thumbnail is correct, as you can see here:

If I use it for a PDF with landscape pages, the devicewidth is taken as height somehow:

How can I prevent this behaviour? I want my Porsche to be 90x120 as well. I think maybe i need to provide some Postscript code for Ghostscript (with -c command line argument), but I have no experience with that. Could someone please help me?

EDIT1: I tried the suggestion of KenS. With the -dFIXEDMEDIA my porsche gets cropped like you can see below:

EDIT2: first solution of Kurt Pfeifle is not ok for portrait images (white part right side, not using space properly). See below:

EDIT3: third solution of Kurt Pfeifle is almost good. For landscape images its perfect:

However, the portrait pages have sizing problems, and the background becomes completely gray as well:

So Kurt, i think I could split the pdf to pages (with GS -dFirstPage and -dLastPage), and then if you have some idea, how to decide if a page is landscape or portrait, then I could do some conditional processing. Any idea? As for background color, I think its not that important, but if you have ideas here as well, then they are welcome.

解决方案

Ok, now trying with a more elaborated answer, based on the above mentioned idea of 'manipulating the PDF first (so that it uses a portrait media format to display its landscape image contents)'...

Note, since your original PDF doesn't use a common size for all pages (they all are different), I did my proof of concept with the first page only.

Step 1: Extract page 1 from the original (landscape)

I'm using pdftk for this:

porsches.pdf  cat 1  output porsche-page1.pdf

Step 2: Center landscape content on larger portrait page

I'm using Ghostscript plus a -c ... PostScript commandline snippet for this:

gs \
 -o porsche-page1-on-portrait-medium.pdf \
 -sDEVICE=pdfwrite \
 -dPDFSETTINGS=/prepress \
 -g1920x2560 \
 -r72 \
 -c "<</PageOffset [0 560]>> setpagedevice" \
 -f porsche-page1.pdf

The /PageOffset values are derived from the fact that I added 1120 points to the original page height of 1440 points. Therefor I shift the contents by half the value upwards so the picture is again centered.

Step 3: Create the JPEG thumbnails (portrait)

gs \
 -sOutputFile=proofofconcept-thumb_%03d.jpg \
 -dPDFFitPage \
 -dDEVICEWIDTH=90 \
 -dDEVICEHEIGHT=120 \
 -sDEVICE=jpeg \
  porsche-page1-on-portrait-medium.pdf

Unless I didn't utterly mis-understand what your intention was: this should be the result that you wanted. (Note: I added a black frame to the thumbnail image to make its true dimensions visible even on the white HTML background of Stackoverflow.)

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