Inkjet Proofing

Hello again,

The most interesting area I've been involved during these months of absence from the blogging community was inkjet proofing. There are plenty of variables involved in this process.

The simplest and most reliable way to inkjet proofing is continuous tone proofs. I am not very interested in discussing continuous tone proofs, as there are plenty of software packages that are able to provide a reliable proof with certain pre-engineered color management algorithms. They certainly need their mastery and a critical visual evaluation, but the calculations, after approximately three iterations of optimization, can provide results that are really close to a visual target. In that, either EFI's rip or ORIS Color Tuner, provide very good results (i'm not all inclusive here... this is just what i tried). Then, certain adjustments for visual match give a very good proof.

Where do the complications of inkjet proofing start?

1. The white point of the target paper and absolute colorimetric intent.
2. Banding.
3. Halftone proofs
4. Hexachrome proofing
5. The color of black

To begin with:
1. WHITE POINT
Mapping the white point of the target paper through absolute colorimetric intent is not always perfect. Introducing the LAB value of the target paper into the proofing media alters the color of the proof. This is obvious especially in the highlight regions where the yellowness or blueness is introduced in the light areas. This problem is dealt with certain software packages where the user is able to affect only a small region of the color gamut. Relative intent works much better, but at cases where the target white points differs significantly from the proofing medium, there is a discrepancy that might be confusing to the press/customer. It is nevertheless astonishing that the profiling software is not able to map the white point with relative ease. I could make a wild guess and say that this is being caused due to chromatic adaptation, but it would be wild and uneducated.

2. BANDING
I've seen certain banding problems that can only be associated with the color algorithms of certain packages or with the ICC profile itself. I would guess again that the more you tweak a profile the more likely it is banding to occur. Then again, the way the software packages work, by trying to minimize the color difference from the profiling target to the media profile, some clustering of the target LAB values is not unlikely.

3. HALFTONE PROOFS
This is where the party starts. The rest is manageable. There isn't a software that is able to effectively color manage halftone proofs. EFI's rip offers a color management option with halftoning, but my experience is that the moire you get is unsaleable! Then again, you can separate the digital file to 1-bit TIFFs and try to work them around. How is color management applied to four channels that are a. already separated into 1010101 dots and b. translated into 7 or 8 eight channels based on the proofer? Only solution that we came up with was through editing the source profile. Results were decent, but unless my vision is all messed up it takes about 40 iterations, and then again... at some point... you just cannot get any closer to the target, since the above-mentioned clustering that would bring all the colors closer to the target LAB values is impossible through the naked eye. This might be a thesis topic for my valuable friend Arvind (http://cias.rit.edu/printmedia/03_programs/grads/karthikeyan.html) who's been helping me with proofing.

4. HEXACHROME
Ha! Forget about it, especially if you want halftones or spot colors as 7th or 8th channels. Then again, even halftone offset printing is kind of weird...

5. BLACK INKS
This is a colorant issue. Again, depending on the software, the color of the black might be unmanageable. I don't think that EFI has a good solution, as I was getting the cast of the inkjet proofers inks, and that was different from that of the ink supplier. I haven't seen such an issue yet with ORIS software.

In conclusion, inkjet proofing can have very good results in continuous tone proofs. My belied is that inkjet is the way of the future though, and that film based proofs with significantly lose their value, even if they provide higher stability and larger gamut (plus halftoning!!!) at this point of time. It is up to smart color scientists and engineers though to come up wth the algorithms that would eliminate all or some of the factors I discussed above, and -my belief again- that this is only a matter of time.

-D

PS> I would like to mention and thank my friend Rob Seckendorf of Color Correct Solutions, who has been providing his support and expertise with inkjet proofing (www.colorcorrectsolutions.com)