Colour seperations

[scomac]

I designed a stationery package in XaraX and now want ot get it printed. It's a four colour job which needs to be seperated. I've taken the files to my service bureau and we've tried just about everything we can but the black text appears on all the plates. When I look at the colour profile of the black I've chosen it shows as 100% K. I've set the black lines and fills to overprint but it still prints on all the plates. Even when I export it as a tiff file and open in Adobe Photoshop the black is seperated into the four colours ?!? Any suggestions? Thanks

[scomac]

I designed a stationery package in XaraX and now want ot get it printed. It's a four colour job which needs to be seperated. I've taken the files to my service bureau and we've tried just about everything we can but the black text appears on all the plates. When I look at the colour profile of the black I've chosen it shows as 100% K. I've set the black lines and fills to overprint but it still prints on all the plates. Even when I export it as a tiff file and open in Adobe Photoshop the black is seperated into the four colours ?!? Any suggestions? Thanks

[Sean Sedwards]

It's easy to get bogged down in this subject, so I'll keep it brief and you can tell me if I'm getting close.

If you export as XaraX EPS, image setters seem unable to extract the information in the way you'd expect. All colours, including spot, are treated as process and contain a mixture of C, M, Y and K, depending on the algorithm they're using. Remember that the black is only added to make up for the deficiencies of the C, M & Y inks / process; if they were perfect, the black wouldn't be necessary.

If you export as a bitmap it is possible to separate all the black onto its own plate and I'm surprised your bureau couldn't do this. Under Separation Setup in PhotoShop, select GCR (Grey Component Replacement) and choose Maximum Black Generation. All the black will be on the K plate, however this may not be the best setting to reproduce the rest of the image and there may be some 'halos' on the other plates resulting from anti-aliasing. So far I've suggested nothing that couldn't be done by a monkey and a half-decent bureau should be able to enhance the image further.

Option 3 is to print to file using a PostScript print driver (use a Linotronic driver from the Windows install disk if you can't get the one your bureau uses); the resulting PRN file is actually just an EPS and can simply be renamed. Using Xara's Print Options you can print the seps in one file or separately and make a number of other adjustments, such as crop marks and dot type. Note that these setting don't affect EPS export and the automatic transparency resolution setting doesn't always work (this is particularly true for desktop printers). Also, if you don't explicitly check the Print colour separations box, the output will be a composite as per EPS export.

This last technique seems to work best and if you get hold of GhostScript + GSView, you can preview the separations to make sure it has worked.

Regards - Sean

[Sean Sedwards]

Some time ago I posted four plug-ins to separate the C, M, Y and K components of an RGB bitmap using a Max Black algorithm, which I've attached again below. They offer no other form of colour compensation and each plate should be converted to greyscale (to save space) if you want to export them.

You can demonstrate the technique I described in my previous reply by creating four copies of the original bitmap, applying one of the plug-ins to each. To recombine (on the page at least), select each plate in turn, right click on the white colour square then left click on the appropriate separation colour. Arrange the plates centrally and apply 0% stained glass transparency.

Regards - Sean

[viking]

Hi Sean,

i downloaded your plugins for color separation.
it works good, but to much black.
Can you make it the other way round.
Give us only a little black and a lot of color.

I hope you made the other plugins too.
If so give us the possibility to download.

Thanks

viking (I like XaraX)
[EMAIL]viking@ctcinternet.cl [img]/infopop/emoticons/icon_biggrin.gif[/img]

[Sean Sedwards]

Viking

I'm not sure if this is what you had in mind, but I've re-worked the plug-ins and you can now set the threshold at which the black is replaced. The default condition is Threshold = 0, which produces maximum black, as before. Two other special cases are threshold = 255, where no black appears on the K plate (all colours are reproduced as combinations of C, M and Y) and threshold = 254 which allows only pure black (RGB = 0, 0, 0) to be transferred to the K plate.

To make sure the plates re-combine correctly, use the same setting on all filters. Also, don't trust the preview if it isn't 1:1 with the original because the re-sampling alters the colours. This is particularly relevant at the extreme settings where objects can appear in the preview but not in the final bitmap.

Regards - Sean

[viking]

Hi Sean,
many thanks for your quick response to my questions. Your new plugins works fine for Spotcolor Separations. After converting my test archiv "cmyk_rgb.web" and separating the plates i imported them to Photoshop. I had to invert them and convert to grayscale. After merging the channels together i got a color image with exactly the same values as in Xara X. But for separating photos i was not so lucky. I got a 100% tricolor separation + a black without greys on top. I think we need a GCR Separation with lite, medium or maximum black. My idea is that maybe You, the folks at Xara or other programmer (for sale) could make a plugin for automatic Spotcolor and GCR separation with all the futures i was mencioning above. This would help a lot of people. The Printbureaus simply don´t accept RGB files and EPS is very lossy.

Many thanks for your time.
regards
viking (i like XaraX (better with Plugin)) [img]/infopop/emoticons/icon_biggrin.gif[/img]
viking@ctcinternet.cl

[This message was edited by viking on November 17, 2000 at 12:47 PM.]