CMYW Printing ????

[BCELY]

Hi there

This may well be a very stupid question so please forgive my ignorance from the outset.

We have a guy here who wants to prints on non-white material using a 'White Toner' printer.

He's asked if we can convert CMYK images to 'CMYW' and I immeadiatley thought of using ImageMagick as we've used it for other manipulations.

I guessing the process is to take the CMYK file, reconvert to CMY (where the C,M and Y channels also hold the black information) and then insert a 'black' channel which is actually a negative of a grayscale of the original ????

I started by using -colorspace CYM on a convertion but when I take that into Photoshop to see what's happened it's RGB for some reason.

Is ImageMagick the tool for the job or should I be looking else where ?

Any help to this 'newbie' appreciated.

[fmw42]

You could try to create a copy of the image and convert to grayscale. Then invert (-negate) the grayscale image and replace the old K with the negated grayscale. Unix syntax

Code: Select all

convert image_cmyk \
\( -clone 0 -separate \) \
\( -clone 0 -colorspace gray -negate \) \
-delete 0 \
+swap +delete \
-set colorspace CMYK -combine \
image_cmyw

Does that do what you want?

[snibgo]

It may be as simple as Fred says. If not, and you can provide a sample "CMYW" image, and the equivalent sRGB image, we may be able to work out how to do it.

[BCELY]

Hi Folks

That's for the reply.....

@fmw42

I haven't tried your solution yet but I think we'll loose the black altogether using your method - In my mind we'd need to adjust/remix the CMY channel values to 'make' black where appropriate before over witing the black channel. I will however give it a go and report back.

@snibgo

I'll have a chat with the guy and get something uploaded - Cheers

[LuisF]

@snibgo and @fmw42,

I was wondering if you have come up with solution? I was wondering myself if ImageMagick is the way to go. There is a Rip called Icolor TransferRip.

http://www.uninetimaging.com/downloads/ ... nt_ENG.pdf

The Rip uses a CMYK printer to print CMYW when the C and K toner/drum set, filled with white toner, are physically swapped so that the first toner/drum set is the C set and K toner/drum set is the last set which becomes now a CMYW configuration. The Rip also remaps the C and K channels of the CMY channels, converts black of the image into composite CMY black, Create a black version of the CMY image then underprint or overprint it on the CMY image. Not sure really the order of the sequence. I think by remapping C and K channels the C channel data will be sent to the K toner/drum set position where the C toner/drum set now resides and the K channel data will be sent to the C toner/drum set which is now K toner drum set position. Do I make sense? Can this be done with ImageMagick?

BTW Forever TransferRIP uses ImageMagick based on the list of files in that package. ImageMagick files are included in the package. But Forever TransferRip does not remap C and K channels and it only works with CMYW WT printer.

LuisF

[fmw42]

try just inverting the K channel to make it white instead of black

Code: Select all

convert image_cmyk -separate +channel \
\( -clone 3 -negate \) \
+swap +delete \
-set colorspace CMYK -combine \
image_cmyw

(some suffix like .jpg or .tif needs to be added to image_cmyk and image_cmyw)

[LuisF]

I tried it but I am getting "-iclone no such image" error when I used smile.jpg for image. When I changed "-clone 3" to "-clone 2" i don't get the error. When I opened it in Photoshop the C and K channels were not swapped.

[fmw42]

Is your image CMY or CMYK? If the former, then there is no K channel and thus no -clone 3 (numbers start at 0). Might your image be sRGB, that would also only have 3 channels and thus no -clone 3.

Post your image to some place such as dropbox.com and put the URL here. Or post the output from

Code: Select all

identify -verbose yourimage

What is your IM version and platform? Please always provide that.

[LuisF]

OK I will try a CMYK image. I will post the output after conversion.

[LuisF]

BTW I can swap C and K channels by doing the following:
1) Create workpath and save it
2) Convert RGB to CMYK
3) Duplicate C channel
4) Delete the original C channel. Photoshop flattens the image and converts it to Multi channel mode
5) Use the path as selection
6) Hide CMY
7) Fill the selection with black
8 ) Swap C and K channels
9) Convert the Image to CMYK

The Image will have dark Cyan bluish cast. But when the C channel which is now filled with black is hidden the image looks normal. It is almost like it is going to work when I swap the C and K toner/drum set filled with white toner then print it but black is more like brown and Cyan is very pale. The CMY is printed over with white toner. I need to convert the image to CMY first so the black and gray of the image will be composite of CMY.

How can I convert RGB to CMY with ImageMagick so that the black and gray of the image is composite of CMY?

[fmw42]

Have you tried

convert image_rgb -colorspace CMY image_cmy

Again, please always provide your IM version and platform.


Why would you want to swap C and K?

Perhaps you should provide an example input and the desired output that is compatible with whatever printing system you have.

I do not think any of us understand what your printer requirements really are? We do not understand the format for CMYW unless it is what I suggested above by inverting the K channel (-negate) to a W channel. Having a proper example of the compatible format may help us figure out how to created it.

[snibgo]

@LuisF:

Most printers come with drivers. This is software that can accept ordinary images (such as sRGB) and convert it to whatever the printer wants, according to whatever inks it has. (Some printers have light-cyan, different shades of gray, etc.)

If you have a printer (or printer driver) that takes some other file format with a "white" channel, we can only guess as what data might be needed.

If you can provide a sample file with "white", and the corresponding sRGB file, perhaps we can help. Or if you can provide technical documentation that describes the format, that would also help.

[fmw42]

Perhaps I misunderstand and you are starting with an sRGB image. If so, then try

Code: Select all

convert image_cmyk -colorspace CMYK -separate +channel \
\( -clone 3 -negate \) \
+swap +delete \
-set colorspace CMYK -combine \
image_cmyw

[LuisF]

Here is the link to the Description and folder with original file, your codes output and the modified output in photoshop.
https://www.dropbox.com/s/qv5twzjvkdstm ... s.pdf?dl=0

Link to Folder of original and output files:
https://www.dropbox.com/sh/66u3qyhzv9td ... EqQ2a?dl=0

Hope my explanation is clear.

Luis

[snibgo]

Do you have a file that does what you want with your printer?