Ghostscript中的CMYK叠印和淘汰 [英] CMYK Overprinting and Knockout in Ghostscript

问题描述

我正在尝试了解当前版本的Ghostscript的功能（另请参见这个问题（我几天前问过）。因此，我从瑞士的标准组织www.pdfx-ready.ch下载了PDF / X-4标准的测试表格，并尝试进行渲染...（如果有人想尝试一下，这里是直接下载链接： http：//www.pdfx-ready .ch / files / PDFX-ready-OutputTest_PDFX4-CMYK_V301d.zip 。您可以在此页面（德语）上找到更多信息： http://www.pdfx-ready.ch/index.php?show=496 ）

I'm trying to get a grasp on the capabilities of the current version of Ghostscript (see also this question that I asked a few days ago). So, I downloaded a "test form" for the PDF/X-4 standard from www.pdfx-ready.ch, a standards organization in Switzerland, and tried to render it... (In case anyone wants to try this, here's the direct download link: http://www.pdfx-ready.ch/files/PDFX-ready-OutputTest_PDFX4-CMYK_V301d.zip. You can find more info on this page (in German): http://www.pdfx-ready.ch/index.php?show=496)

无论如何：令我惊讶的是，大多数测试字段都在屏幕上正确呈现。我尝试过的大多数其他PDF查看器都失败了。然后我注意到有些测试用例产生了错误：

Anyway: I was pleasantly surprised to see that most of the test fields were rendered correctly on screen. Most of the other PDF viewers that I had tried had failed miserably. Then I noticed that there were a few test cases that produced errors:

• CMYK套印模式（第1页） ）不适合字体和
  矢量使用（对图像，蒙版和阴影效果很好）。


• 敲除透明组的渲染（第2）执行不正确。


• 渲染更多与套印有关的字段（第4页）（点到CMYK，点到CMYK ，图像叠印等）失败。

• CMYK Overprint Mode (on page 1) is not respected for fonts and vectors (it works fine for images, masks and shadings).
• Rendering of Knockout Transparency Groups (on page 2) is not performed correctly.
• Rendering of a few more fields (on page 4) that had to do with overprinting (Spot to CMYK, CMYK over Spot, Image Overprint etc.) failed.

因此，我开始进行实验...首先，我注意到我仍然有旧版本的安装了Ghostscript。因此，我编译了新的版本9.16 并再次尝试。这次，剔除透明组（请参见上文）已正确呈现。太棒了！

So, I started experimenting... First I noticed that I still had an old version of Ghostscript installed. So, I compiled the new version 9.16 and tried again. This time, the Knockout Transparency Groups (see above) were rendered correctly. Great!

然后我阅读了此处套印和专色的处理取决于输出设备的原色模型。因此，我现在尝试使用 -sDEVICE = x11cmyk 而不是 -sDEVICE = x11 。令我惊讶的是，有关CMYK套印模式的错误消失了。不幸的是，第4页上的错误仍然存​​在。

Then I read here that "the handling of overprinting and spot colors depends upon the process color model of the output device". So, instead of -sDEVICE=x11 I now tried -sDEVICE=x11cmyk. And to my surprise, the errors regarding the CMYK Overprint Mode went away. Unfortunately, the errors on page 4 remained.

此外，我现在遇到两个新问题：首先，页面现在呈现为错误的颜色。实际上，测试页的白色背景现在显示为青色！另外，似乎Ghostscript现在正在尝试在屏幕上模拟某种难看的半色调。我再次阅读此处，即 daccess-ods.un.org daccess-ods.un.org由输出设备的颜色模型差异引起的带有套印和专色的文件不是由于Ghostscript或其输出设备的实施限制。 我错过了一些东西。

What's more, I now have two new problems: First of all, the pages are now rendered in wrong colors. In fact, the white background of the test pages now appears in cyan! Also, it seems, Ghostscript is now trying to simulate some kind of ugly halftoning on screen. I read here again that "The differences in appearance of files with overprinting and spot colors caused by the differences in the color model of the output device [...] are not due to a limitation in the implementation of Ghostscript or its output devices." So, I'm assuming that I'm missing something. But what is it?

总结：

• 有没有办法（也许其他设备，命令行参数等）告诉Ghostscript正确处理叠印？还是尚未实施？


• 是什么原因导致白色背景出现青色？


• 有没有办法将其正确打印到喷墨，它在屏幕上的显示方式？ （lpr似乎工作不正常。）

预先感谢。

因此，我做了很多实验并阅读了一些讨论。另外，文档此处，我发现它很有趣，因为它说：

So, I experimented a lot and read a few discussions. Also, the documentation here, which I found pretty interesting, as it says:

当渲染到分离设备 psdcmyk时，Ghostscript当前为现货
着色剂提供套印模拟 code>和
tiffsep 。这些设备维护所有专色平面并将
合并在一起以提供模拟预览
打印出来。

"Ghostscript currently provides overprint simulation for spot colorants when rendering to the separation devices psdcmyk and tiffsep. These devices maintain all the spot color planes and merge these together to provide a simulated preview of what would be printed."

好的，这就是@KenS（见下文）在评论中提到的内容。但是随后

Alright, this is what @KenS (see below) mentioned in a comment. But then




通过指定 CMYK设备获得套印的模拟预览> -dSimulateOverprint = true / false在这种
情况下，通过混合
CMYK着色剂来实现模拟叠印。 [p.9]

"It is possible to get a simulated preview of overprinting with other CMYK devices by specifying -dSimulateOverprint = true/false In this case, simulated overprinting is achieved through a blending of the CMYK colorants." [p.9]

现在，我的意思是说我可以使用CMYK设备（例如 tiff32nc ）来获得带有专色套印的模拟预览。我对么？因此，在此处进行更多阅读之后（以防万一，这有什么用使用CMYK，我对此表示怀疑），我终于尝试了以下操作：

Now, I read that as saying that I can use a CMYK device (like tiff32nc) to get a simulated preview of overprinting with spot colors. Am I correct? So, after some more reading here (just in case this has anything to do with CMYK, which I doubt), I finally tried the following:

gs -dBATCH -dNOPAUSE -dSAFER
   -dSimulateOverprint=true
   -sDefaultCMYKProfile=ISOcoated_v2_300_eci.icc
   -sOutputICCProfile=ISOcoated_v2_300_eci.icc
   -sDEVICE=tiff32nc
   -sOutputFile=out.tif
   in.pdf

我什至尝试了 -dOverrideICC 选项， code> -dRenderIntent 和 -sProofProfile 。似乎没有任何作用。我在这里误会什么？

I even experimented with the options -dOverrideICC, -dRenderIntent and -sProofProfile. Nothing seems to work. What am I misunderstanding here? Is there really no way to render a non-seperated full-color preview of correctly overprinted spot colors?

所以，我终于尝试了 tiffsep 设备（不是我想要实现的，但作为测试用例很有趣），并检查了生成的五个文件。而且还有仍然错误！如果要检查，请运行命令

So, I finally tried the tiffsep device (not really, what I would like to achieve, but interesting as a test case) and checked the five files that are produced. And there are still errors! If you would like to check, run the command

gs -dBATCH -dNOPAUSE -dSAFER
   -sDEVICE=tiffsep
   -dFirstPage=4
   -dLastPage=4
   -sOutputFile=page4.tif
   PDFX-ready_Output-Test_301d_X4.pdf

在上述PDF / X-4文档中。然后检查例如左列第一行中的第三个测试字段（第4页）。

over the aforementioned PDF/X-4 document. Then examine, e.g., the third test field in the first row in the left column (page 4).

所以，我真的不知道该怎么做。这是否意味着Ghostscript根本无法处理带有专色的叠印-与文档中所说的相反？那是个错误吗？还是我的命令错误？我有什么遗漏吗？

So, I really don't know what to make of this. Does that mean that Ghostscript can't handle overprinting with spot colors at all - contrary to what the documentation says? Is that a bug? Or do I have the command wrong? Am I missing anything?

推荐答案

第一个答案是停止尝试使用X11设备，它是RGB设备并且没有得到很好的支持。为了执行X11CMYK，必须将输入呈现为CMYK，然后进行后期滤波为RGB。

First answer is stop trying to use the X11 device, its an RGB device and not hugely well supported. In order to do X11CMYK the input must be rendered to CMYK then post filtered to RGB. Its not a good solution.

套印仅针对CMYK印刷色（和专色）定义，任何其他颜色模型均不会套印。因此，我建议您使用其CMYK变体来渲染TIFF或JPEG设备。

Overprinting is only defined for CMYK process colours (and spots), any other colour model will not perform overprinting. So I would suggest you render to TIFF or JPEG devices using their CMYK variants.

专色甚至更复杂，如果设备不支持所要求的专色，那么它会使用色调变换将其转换为定义的备用颜色空间。如果进行了色调转换，则不会套印专色。

Spot colours are even more complex, if the device does not support the requested spot colour then it uses the tint transform to convert into the defined alternate colour space. If tint transformation takes place the spot is not overprinted.

由于显示设备不支持专色，因此无法使用显示设备预览专色套印。如果要执行此操作，则应使用tiffsep设备。

Since the display devices cannot support spot colours, you can't preview spot overprinting using a display device. If you want to do this you should use the tiffsep device.

如果您相信自己在Ghostscript中发现了一个错误，请报告此错误，但您将将其报告给CMYK设备，现在我要说的是，我们不会对X11 CMYK设备中的错误非常活跃，因为它实际上没有使用过。

If you believe you have found a bug in Ghostscript, then please report it as such, but you will have to report it against a CMYK device, and I'll say now that we won't be very active with bugs in the X11 CMYK device, its practically unused.

打印喷墨设备的连接取决于打印工作流程，我不知道您要使用什么。如果它的CUPS（而且我仅根据您使用的是X11设备来猜测），那么应该就可以了。但这取决于完整的端到端打印过程，我不知道它在做什么。

Printing to an inkjet device depends on the printing workflow, and I have no idea what you are using for that. If its CUPS (and I'm guessing solely based on the fact that you are using an X11 device) then this 'should' just work. But it depends on the complete end-to-end print process, and I have no idea what it is you are doing.

再次注意，专色将不可用在CMYK打印机上，因此叠印斑点可能无法按您期望的方式工作。

Again note that spot colours will not be available on a CMYK printer, so overprinting spots is probably not going to work the way you expect.

这篇关于Ghostscript中的CMYK叠印和淘汰的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！