Wednesday, October 6, 2010

Inkscape Does Support CMYK

While some are mislead by the fact that Inkscape does not (and probably should not) support raw or "generic" CMYK, it does in fact support working with true CMYK for print support. The key factor is that Inkscape only supports real CMYK work, and not "pretend CMYK." In and of itself "CMYK color" does not mean anything specific. It turns out that "RGB color" is also meaningless as far as specifying an actual color goes, but the variances are usually not as strong. To get accurate RGB color, one needs to specify *which* RGB to use. SMTP television values, Adobe RGB, Wide Gamut RGB, sRGB, etc. For experience on the Internet, people usually don't realize that there is an implied colorspace of "sRGB" used for tools, browsers, etc.

In a similar manner, Inkscape needs to be given a *specific* CMYK colorspace to work in. In fact, Inkscape (and SVG itself) can support a document with several different colorspaces at once, including mixing multiple different CMYK colorspaces alongside RGB colorspaces. This could be useful for cases such as when a graphic designer is creating artwork for some brochure that will be printed with cutaways and different paper types. Or it could apply to a case where different printers are used for different parts of a job. (Figure 1 shows what appears to be the same colors)

However an fairly common use case is where one might create a document to be printed mainly in CMYK, but with one or more spot colors, such as Pantone, Toyo, HKS, etc. colors. In this case, some elements of the artwork can be marked with a specific target CMYK profile, while the elements to be done in a spot color can be specified with a named color profile supporting the type of spot color (for SVG 1.2) or perhaps even with simple sRGB equivalents. Then when things go to a service bureau to be run the CMYK elements can go to a four-color print and the spot colors can go to custom plates per ink. (Figure 2 shows that the colors are actually different)

So how does only get to "real CMYK" in Inkscape? It's actually fairly simple. First at least one CMYK profile needs to be added to the document being worked on. That can be accessed in the GUI through the "Color Management" tab on the document properties dialog. Once at least one profile has been added, the color pickers in the Fill & Stroke dialog can be used to pick colors in that colorspace via specifying the ICC profile. In the past one needed to use the CMS color picker, but with Inkscape 0.48 the other color pickers such as the "CMYK" one will attempt to preserve values. (Figure 3 shows that the exact same CMYK numbers were used)

The main problem left is that even though true CMYK values are stored in the saved SVG value, using those values is now a bottleneck. Printing directly from Inkscape will flatten things to sRGB, and even PDF export will not yet preserve the CMYK values However, other software can read and use those values. Recent versions of Scribus will read in and preserve ICC colors including CMYK, and will happily save high-quality print-ready PDF output. (Figure 4 reveals the difference in RGB and visible colors that result from using two different CMYK profiles)

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Monday, September 20, 2010

"CMYK" is Meaningless

For anyone working with print there is one key principal to keep in mind: "CMYK numbers" are meaningless. Far too often artists are lured into "working in CMYK" without actually understanding what it means, and fall into the trap of believing their work is more precise when the exact opposite is true. Saying "50% Cyan" does not actually specify any color, and will most likely result in many different colors being produced. The subtle yet critical difference between "untagged CMYK" vs. "unspecified CMYK" is the bottom line that will mean the difference between success and failure.

CMYK is a type of colorspace, but in and of itself does not actually specify anything. It just tells how one can define a specific colorspace. To actually make sense a specific device (either real or theoretical) needs to be targeted. Once the specifics are involved, however, working in a specific CMYK is a very helpful thing. It is good to try to not get caught up in distraction of focusing on the "how" of things and instead look to the "why" of doing things.

In this case, the distracting "how" is people "working in CMYK" while the "why" they should be focusing on is reliably creating and controlling color. Instead of an artist getting caught up in saying "I need to get exactly a 50% saturation of cyan ink onto the printing plate at this point", they need to shift to say "I need to get this point of the final print output to be exactly this shade of color." That is not to say that an artist should never be concerned about CMYK numbers and plate separations, but rather they need to keep in mind that the ink details are merely a means in reaching the ends of the final print. (There is one main exception to the focus on raw CMYK, but I'll cover that later)

So although 'raw CMYK' numbers might be meaningless and produce randomly shifting results in completely unpredictable ways, CMYK values in a specific context normally give very precise and controlled output. Be wary of anyone asking for or providing "generic CMYK". However, specifics such as "SWOP v2 CMYK" will allow for fairly exact control and results. If someone says "CMYK", the response should be "which CMYK?"

What does this all mean in practice? If one is producing artwork that will go to print, getting specifics nailed down is critical. When working with a good print house, they will provide either specific profiles for the output that will be run, or will say which industry standard profiles they will work from. The artist provides content targeting the specific CMYK profile and then the printed results comes back with the exact appearance that was intended. The print house gets this generally specified input and then does a specific conversion from what the artist supplied to the measured control needed for the specific press and the actual paper with that days inks and the current temperature, humidity, etc.

When such a good workflow is used one can get reprints run at any time later on and the output will match what was printed the past week, month or even year. Thus there is no need for the time nor the expense of multiple tweak-and-reprint runs to end up with acceptable results.

On the other hand, if a small shop is used that employs no color management in their own workflow, the burden falls squarely on the artist/customer to come up with ways to get consistent and desired output. Sometimes the print shop will provide some target profile, but make no guarantees as what the resulting run will look like.

This is the point where most will just think they're working directly with raw CMYK and just need to tweak things over and over until they are close enough. That's actually not what they should be doing. The critical need here is to understand that they are not working in "generic CMYK", but that they are working to a very specific CMYK. They really are working in "CMYK for fliers printed at the corner press". Sometimes that color will be consistent over time, but more often even that will vary from week to week or from day to day. If the artist was smart, he would have created his own profile for the local print shop and will work in an industry standard CMYK and convert to the specific local shop CMYK for delivery to them. He also should have done some simple calibrated output (perhaps in the margins of his run) so that if (or more likely when) the local print shop gives different colors for the same numbers he can call them on it and get things corrected.

For a shop with a good relationship, the artist can use his own management and tracking to get the print shop to correct their output. Some small shops might not even be employing much in the realm of color control but can happily match output to a reference proof they get handed along with the files for the job to be run that day.

Finally in the case were the local print shop will give varying results and no help for color matching we reach the situation I mentioned where actually sending raw CMYK values is desired. However the reason for sending out a file with raw CMYK that is intended to go exactly to the end plates is in creating a test target output for measurement so that the artist can create his own target CMYK profile. The artist can send over a raw file to get a test output print, and then measure that test print. He then converts the real job files to using that locally created profile and sends the adjusted art files over to be printed. The net result is better output with lower costs due to avoiding reprints, etc. (so "raw CMYK values" should really only be used for printing test targets)

This last case helps illustrate the difference between "untagged CMYK" and "unspecified CMYK". The artists sends over art files that are not tagged with any embedded ICC profiles. However these are not raw nor "unspecified" CMYK values at all. Rather they are CMYK numbers in the specific profile that the artist himself has created to describe the characteristics of the local print shop. Although the files are not literally tagged with the profile, they have been created with an explicit ICC CMYK profile specified in the artists workflow.

And the bottom line? Be specific and you will save both time and money. And end up with happier clients.

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Tuesday, March 16, 2010

Backlogs and Real Life

The last three months have been a bit crazy, with far too much "real life" hitting us upside the head. Things have finally settled in a bit so that I'll be able to get my head above water and surface again. Aside from diving head first at the new day job and surviving the holidays, much had happened in the tech world.

I still haven't had time to finish my writeup of SVG Open (partly since I accepted the new day job while I was attending it up in Mountain View). Then there was the Google Summer of Code Mentors' summit. Great things happened there. Then I had to prep for our visit to New Zealand as co-organizer for a Libre Graphics Day miniconf and as a speaker at the main Then we had SCALE8x come 'round where I presented yet another talk and then also run the Inkscape booth on the show floor. Toss in getting a new tech (adaptive UI) going, starting a new project with other CREATE guys, and doing battle across the board to help get proper CMYK support out for end users everywhere.


On top of all that was work for Inkscape and trying to get new features solid for the next release, 0.48. Thankfully I was able to squeeze the time in to finish up the basic support and UI for per-document color/swatch palettes. This allows for basic colors to be stored as a set in a given document, but also for gradients to be included in that. One big thing that inclusion accomplishes is breaking down the artificial barriers software engineers have imposed on artists for far too long. Assets had been artificially separated by their *implementation*, without regard for how artists actually are used to working. This also enabled many workflow enhancements including making art recoloring easier, indicating which swatches are in use on the selected object, etc.

Work on the new input devices dialog also came through. Aside from more end users getting their hands on tablets and such, we had a push in that the ugly outdated GTK+ dialog is being removed. And just in the nick of time we had Krzysztof step up and investigate some of the win32 tablet bugs and get some insight on the problem with Aiptek and others showing up with broken names. I was able to help refine the fixups there wile getting them set to be reimplemented in the new dialog.

And then there is the basic work on adaptive UI. This is a very promising area, and is just beginning to show the tip of the iceberg. I'm implementing internals based in part on Michael Terry's work with INGIMP he has presented at LGM. Though 0.48 will only expose a tiny bit of what can go on, the support in Inkscape will give it some very useful functionality in even the near term. We're looking at only giving 0.48 a few set layout modes, but with some handy logic behind the scenes to assist users getting what they need without having to think as much.

Unfortunately, though, we were unable to find time to work in support for Wii remotes, joysticks, and the SpaceNavigator someone at LCA lent me. We are on track to get more in, and 0.49 might even see some of that. Some of this (like using guitar game controllers) might sound a bit silly. However there are some very interesting ways these can be worked in and give Inkscape some nice functionality for average users. And, of course, more hardware toys always makes the geeks happier.

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