I'm trying to use Ghostscript to convert PDF files which have RGB colors into CMYK colors. The blue colors in my PDF get converted into DeviceCMYK just fine. However, pure white colors (i.e. RGB 255, 255, 255) don't show up in the CMYK separation when I do Output Preview in Adobe Acrobat. When I use Acrobat's Object Inspector, it reveals that my white colors have ColorSpace=DeviceGray and ColorValues=1.0 (i.e. white).
This is the simplest form of the command I'm using:
ghostscript\gswin32c.exe -sDEVICE=pdfwrite -dBATCH -dNOPAUSE -sColorConversionStrategy=CMYK -sOutputFile="cmyk.pdf" "rgb.pdf"
I would like to force these white colors to be ColorSpace=DeviceCMYK and ColorValues=0, 0, 0, 0. (This is what Acrobat's Convert Colors produces). How can I do that? I tried hunting through the documentation and trying out various switches that I didn't fully understand, but the result was always the same so far.
If it matters, the version of Ghostscript is 9.21
Input and output files can be downloaded here: https://ufile.io/f/faxbb
It's quite simple, you can't do that. The pdfwrite device regards DeviceGray as a subset of CMYK (it's the K channel) and if it finds a DeviceGray colour it will retain it as such. However, true RGB colours ought to be converted to CMYK.
You haven't supplied the original file so I can't inspect it or try it.
You should upgrade, 9.21 is 3 years old, 9.53.0 was released today.
Edit
I checked the code and this is actually an optimisation. C=M=Y=0, K=% or R=G=B are converted into DeviceGray when written out (ONLY if you are using ColorConversion though!). This is because a single component floating point is smaller to write than three floating point values, so you get a smaller PDF file.
If any profession printing service fails to print colours in DeviceGray I'd be shocked. I'd also be looking for a new printer!
Related
I'm trying to convert an EPS file with an embedded TIFF that has a transparent background to a PNG using GhostScript. The problem that I am having is that the background of the TIFF image becomes white in the PNG. It looks like the following:
IncorrectPNG
When I export from Adobe Illustrator, it comes out correct:
CorrectPNG
I was reading that there is not transparency in EPS, only marked and unmarked areas. I was wondering if there was a call that I was missing that would create the PNG through Ghostscript similar to that of Illustrator? Or if there is any other alternative that doesn't just replace white with transparency through ImageMagick?
I am using Windows and have Ghostscript 9.25 installed. Here is the command (one of many) that I've tried:
-q -dQUIET -dSAFER -dBATCH -dNOPAUSE -dNOPROMPT -sDEVICE=pngalpha -r300 -dEPSCrop NamePlatePNG.png NamePlate.eps
I can get the EPS file to you if needed. Any help would be appreciated, thanks!
UPDATE:
Here is the EPS file (Hopefully this link works):
https://drive.google.com/open?id=1m4HHGLoPe0jdWkx1Oghe7ttiXPldZnJs
Also, I should have mentioned that the images I uploaded were just screenshots of the PNGs open in an image editor. The checkered portion is indeed fully transparent alpha channel. I was trying to easily accentuate the difference.
Your file doesn't look like its transparent, it looks like its masked, possibly with a stencil mask, possibly chroma-keyed. Without seeing the file I can't tell for sure.
You are correct that PostScript (and hence EPS) doesn't support transparency, but it does support several features which have somewhat similar effects.
The color space is irrelevant, and in fact the only kind of 'transparency' supported in PostScript works when the color space is CMYK, but not when its RGB (and certainly not sRGB, which isn't even a PostScript color space, you have to manufacture it from CIEBasedABC)
As far as I can see the command line you are using is correct, but as I say I can't tell much without seeing the actual EPS program.
[EDIT]
So the Ghostscript rendering is correct, that's what is in your EPS file, there is no transparency of any kind there. So how is Illustrator able to make a transparent PNG ? Well the answer is that Illustrator isn't using the PostScript part of the EPS file.
About 1/3 of the way through the EPS file you'll see a line which reads:
%AI9_PrivateDataBegin
What follows that is an Adobe Illustrator file format. When AI reads the file it finds that line, throws away the PostScript portion of the file, and reads the AI representation of the content from the portion of the file beginning with that comment.
Now stored somewhere in there will be the information that portions of the content are transparent. Although PostScript can't represent that, Illustrator's internal format can. So when you write a PNG file from Illustrator it knows that portion is transparent and writes it as such.
Ghostscript, however, is constrained by the PostScript portion of the file, it can't read the Illustrator native format, and so renders the image with a white background.
It 'might' be possible to save a different kind of EPS from Illustrator (level 3 instead of level 2 possibly, I notice this is a language level 2 EPS file) which duplicate the effect, but from what you have here, there isn't anything a standard PostScript interpreter can do which will give you the result you want.
I am using ghostscript 9.25 windows.
I am trying to convert RGB pdf to CMYK preserve pdf using following command:
gswin32c.exe
-dSAFER -dBATCH -dNOPAUSE -dNOCACHE -sDEVICE=pdfwrite -sColorConversionStrategy=CMYK -dProcessColorModel=/DeviceCMYK -dAutoFilterColorImages=false -dAutoFilterGrayImages=false -sOutputFile=out.pdf input.pdf
input.pdf file here
https://www.dropbox.com/s/8jfnov526nhb9m9/blank.pdf?dl=0
output.pdf file here
https://www.dropbox.com/s/ftrmm32mmixaxqh/out.pdf?dl=0
but my output becomes light compared adobe output, expected result is it should be dark when i do in adobe CMYK preserve option, i am getting little dark compared to ghostscript output. Am I doing anything wrong?
Should I use any icc profile?
Thanks
You say you are using ImageMagick, yet you give a Ghostscript command line....
I presume that when you say CMYL you mean CMYK.
There is nothing immediately obviously wrong with your command line, but you have given no example file, nor any reason why you expect the result to be 'dark'.
If you want to control the conversion then you will need to supply at least one and possibly up to 4 ICC profiles. You will certainly need a CIE->CMYK Output profile, and you might like to supply ICC profiles for Gray->CIE, RGB->CIE and CMYK->CIE as well, in order to override the default ones Ghostscript is using.
[EDIT]
The problem is nothing to do with colour conversion. Your original file contains nothing except a very large image, which is compressed with the Flate filter (lossless). It looks like this:
You've turned off auto filtering, but you haven't told Ghostscript which compression filter to use for images, so it sticks with the default, which is JPEG (DCT). The image now looks like this:
For the nature of your original image, JPEG (lossy) compression is an outstandingly bad choice. The output image compresses less well, and it loses fidelity. You should change to using Flate compression instead of JPEG for images of this kind.
By the way, the image in your original PDF file was defined in CMYK space already.
Is it possible to check if a PDF is CMYK or RGB using GhostScript?
I am aware of the inkcov feature, but this just returns values in terms of CMYK (with silent conversion)?
Is the real check, a check for RGB colours or RGB images within the PDF? not sure if both RGB and CMYK images can exist in the same PDF?
Images aren't the only thing that can be in a PDF file, you can also have text, linework and shadings. Also transparency blending can be specified in specific colour spaces. Colour spaces are not limited to RGB or CMYK but can also include Gray and spot (Separation) colours, as well as ICCBased colour spaces and certain specific CIE colour spaces such as Lab.
All of these colour spaces can potentially be present in a PDF file simultaneously.
Ghostscript doesn't contain any tools currently to tell you what colour spaces are used in a PDF file, though the pdf_info.ps script could be modified to do so for unusual (not grey/RGB/CMYK) spaces. You could also write a small piece of PostScript which could tell you when a colour space was used, and what kind of colour it is.
The inkcov device is a CMYK device, so all colours specified in the PDF are converted to CMYK before being 'printed' to the inkcov device which counts up the coverage. It doesn't tell you anything about the original PDF file.
My understanding is that a PDF can contain both RGB and CMYK images, so you'd need to have a tool that can review all images and report on their mode.
If GhostScript doesn't include options to do so, you may have to write a script to use a PDF library for parsing the image and reporting details on the elements it contains.
For example, this Cam::PDF module in Perl says it can parse any PDF v1.5 formatted file.
I'm building an application which uses Ruby+RMagick to composite PNG images onto various JPEG backgrounds. Everything is working, but we have found one particular JPEG background for which the PNG is composited as a black spot. PNG transparency is respected; the shape of the "spot" is correct, but the colors are being lost and becoming black.
I have tried many JPEGs to try to find another which yields the same result, but (so far) have failed.
I suspect that it may have something to do with the bit depth or some other parameter of the JPEG file in question. I have been searching the Internet, looking for a tool which can analyze this JPEG and tell me all the parameters which might be relevant, but haven't found anything yet.
Has anything like this ever happened to you? What was the cause?
Based on your knowledge of the JPEG format, are there any other parameters which might be relevant?
Do you know of any tool which can analyze JPEG files, and tell me the bit depth and other parameters? Or if I open the JPEG in a hex editor, can you tell me how to find this information?
I still haven't found what is special about that one JPG which the composite operation doesn't work correctly on, but I worked around it using this code:
back = Magick::Image.from_blob(jpg_data).first
png = Magick::Image.from_blob(png_data).first
page1 = Magick::Image.new(back.columns, back.rows)
page1.composite!(back, 0, 0, Magick::OverCompositeOp)
page1.composite!(png, png_x, png_y, Magick::OverCompositeOp)
Rather than:
back = Magick::Image.from_blob(jpg_data).first
png = Magick::Image.from_blob(png_data).first
page1 = back.composite(png, png_x, png_y, Magick::OverCompositeOp)
Here is an image:
This image is a simple black-to-transparent gradient saved in full RGBA PNG.
Here is the same image, converted to indexed-alpha PNG by GIMP (Photoshop produces the same result)
As you can see, the gradient is now half-opaque, half-transparent.
Here is the same image again, only this time it was converted to indexed-alpha PNG by a PHP script I wrote:
So my question is: Why are GIMP and Photoshop unable to support partial transparency in indexed images, when the PHP script clearly shows that such an image can be created with no problems?
Is there anything "wrong" with an image whose pallette contains alpha information?
A more programming-related question: Does this transparency in the last image work in Internet Explorer 6?
I've finally found the actual answer: There is a metadata entry that allows you to define the alpha value of each colour in the colour table. Most graphics programs don't make use of this, but it does exist and can be used, in particular by GD.
Another option besides fireworks is pngquant, a command line application that will convert a rgba png into an indexed png with transparency.
I found this post which talks some more about how to use it.
IE6 and earlier in windows does not support variable transparency PNGs without annoying workarounds. An indexed PNG will only show the fully opaque parts which usually works pretty well. A drop shadow would disappear but the opaque parts of the logo or icon would continue to show.
This page has a better explanation and instructions with more png compression and quantization tools: http://calendar.perfplanet.com/2010/png-that-works/
For the record, PNG does not literally support indexed images with an alpha channel. What is really happening is that PNG allows you to add additional colors to the color table (i.e. index) with alpha values in those colors... not a complete alpha channel. FWIW...
Yeah I know what you mean. Fireworks is the only image editing program that I know of that can create and edit PNG8+Alpha without problems. I wish more paint programs would support this format cause Fireworks is expensive!
I found a way in GIMP to create or convert an image with reduced color palette and alpha channel.
The trick is to add a mask to the layer.
Full steps to reproduce:
Have your image in one layer
Add a mask to the layer. Select Transfer layer's alpha channel.
Convert to Indexed (Image -> Mode -> Indexed...)
Save as PNG
Now your image has reduced colors and reduced size, but it keeps your smooth transparency.