Graphics, Figures & Tables ⇒ Do you really need to convert JPGs from RGB to CMYK?!

[insipidtoast]

Are printers basically trying to make life difficult? How do I even know if my digital images are alread in CMYK or not? How the heck do you convert them? Can't they just print the images properly when they are in RGB mode?

I'm really frustrated, because I might have to go back through 84 figures and convert then replace them.

[insipidtoast]

Anyway, if this conversion is really necessary, then is there a quick way to do it using lyx. Or will that affect the image quality negatively. Should I convert each image externally using some other program?

[nlct]

Are printers basically trying to make life difficult? How do I even know if my digital images are alread in CMYK or not? How the heck do you convert them? Can't they just print the images properly when they are in RGB mode?

No, unfortunately they can't. Printers use cmyk ink and there's no one-to-one mapping between rgb and cmyk, which is why they insist on cmyk files. I have a free application that can convert a pdf file to cmyk, which may work for your document as long as your images don't contain any transparency.

Regards
Nicola Talbot

[insipidtoast]

OK, I might end up using that, depending on the printer I go with.

However, I was reading, and it doesn't sound like it's even necessary:
http://garmahis.com/tips/why-avoid-rgb- ... ore-print/

[kaiserkarl13]

You can use something like \usepackage[cmyk]{xcolor} to get PDFLaTeX to convert all colors to CMYK for you. I'm not 100% certain whether that includes embedded JPEG files.

There is also an option to the "convert" command (part of ImageMagick) for many GNU-based operating systems that will do it:

Code: Select all

convert RGB.tif -colorspace CMYK CMYK.tif

[insipidtoast]

Which of all these options will preserve the image quality the best?

I'm not 100% certain whether that includes embedded JPEG files.

I don't have a calibrated monitor or good printer, so I don't think I'll be able to determine if the quality is good.

Nicola, What do you mean by transparency in the image?

[nlct]

Nicola, What do you mean by transparency in the image?

Complete transparency is where you can see through an area of the image. Partial transparency (translucency) is where you can partially see through the image. It's also referred to as the alpha channel, where 0 is completely transparent and 100% is completely opaque. Here's an example:

Code: Select all

\documentclass{article}

\usepackage{tikz}

\begin{document}

\begin{tikzpicture}
\path[fill=red] (0,0) rectangle (10,5);
\path[fill=blue,fill opacity=0.5] (0,0) circle(5);
\end{tikzpicture}

\end{document}

If you compile this using pdflatex, the circle will appear translucent. You can see the rectangle behind it. If you use latex+dvips the circle will be a solid blue and you won't be able to see the corner of the rectangle that it overlaps. This is because PDF supports transparency but PostScript doesn't. So if you want to manipulate a PDF file using PostScript commands (which is what jmakepdfx does) you'll have a problem if there's any transparency.

Regards
Nicola Talbot

[insipidtoast]

How do I know if the images in my pdf have transparency?

Also, how do I know if the xcolor package successfully changed the images in my outputed pdf? What if they look exactly the same as my other test file where I did not apply the xcolor package in the preamble?

[kaiserkarl13]

JPEG does not support transparency---PNG does, though. The PDF drawing in the previous post was done using direct-to-pdf drawing commands (actually through the PGF library, I think it's called).

Did you have any luck with the imagemagick commands ("convert" in GNU-based systems)? That sounds like the best way to handle things.

By the way, I'm surprised that a printer that's uppity about CMYK vs. RGB isn't upset about taking JPEGs in the first place. Most printers I've ever dealt with want either EPS or TIFF images, with some of the newer ones accepting PDF instead of EPS (or in addition to).

[insipidtoast]

"imagemagick commands" - that sounds like a completely new thing to learn...and I was just getting the hang of latex commands.

I'm surprised they don't tell me to convert it to Teff and juggle ink cartridges behind my back while trying to recite the ABCs backwards and riding a unicycle!

Damn printers! WTF am I paying them for!?! YOU FIGURE IT OUT PRINTER. I slaved my ass off typesetting this thing.

kaiserkarl, I entered that latex command you showed above in my preamble and then viewed the pdf and saved it, but I can't see any visible differences in the two documents...please see my other thread
http://latex-community.org/forum/viewto ... 718#p72718