tag:blogger.com,1999:blog-1840985738235902482.post1765789089468435198..comments2024-03-27T07:14:48.488-04:00Comments on John the Math Guy: Why does my cyan have the blues?John Seymourhttp://www.blogger.com/profile/11350487038873935295noreply@blogger.comBlogger15125tag:blogger.com,1999:blog-1840985738235902482.post-63768135479353157542014-05-22T10:46:24.749-04:002014-05-22T10:46:24.749-04:00RGB is problematic since there are so many differe...RGB is problematic since there are so many different interpretations. The RGB from every camera is going to have a different spectral response. Often a gamma will be applied right to the data, which means that the numbers are not linear with reflectance, which is what you need. And there are a variety of numbers to put into the gamma curve.<br /><br />RGB will display different on every monitor, since the spectral output is different depending on the type of monitor and the way it's set up. It introduces it's own nonlinearity.<br /><br />Then there are standards... sRGB is at least well defined. And monitors can be calibrated quite well. Then you have rendering intent...<br /><br />And then there are standards for predicting how an ink will look. Those are in L*a*b*, which can be converted back to sRGB. There are a large number of characterization sets that make those translations... <br /><br />So... you have asked a very simple question with a very complicated answer. Probably not what you wanted and maybe not what you need? I dunno what's "good enough" in your case.<br /><br />Now for the quick answer. If you have an RGB value for paper, use that. Does this go to a display or something?<br /><br />You have an RGB value for cyan ink... where did that come from? Can you get paper the same way?<br /><br />If you want to explore this further, I will need a little more context. Send me an email if you like, explaining a bit deeper what you do. john@johnthemathguy.comJohn Seymourhttps://www.blogger.com/profile/11350487038873935295noreply@blogger.comtag:blogger.com,1999:blog-1840985738235902482.post-24818578998268443812014-05-22T08:35:57.497-04:002014-05-22T08:35:57.497-04:00Hi John! Your blog has been very educational for m...Hi John! Your blog has been very educational for me... Learning about how to control color in the pressroom is so much more complicated than I would have guessed. Thanks for making the learning process a lot more fun. <br /><br />I've been trying to adapt the Beer-Lambert law so that I can make these types of ink predictions, and I think I'm getting close. But I'm having trouble integrating the reflectance or spectrum of the paper. Right now I'm using the ink's RGB values as an approximation to its spectrum.... I have to divide by 255, make the prediction, then multiply by 255 to see what color I end up with. Do you happen to know if there's a way to replace the 255 with something that has more to do with how "white" the paper actually is? Thanks!Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-1840985738235902482.post-60190827440396617112012-12-18T11:31:13.327-05:002012-12-18T11:31:13.327-05:00That's a good idea Paul. You got me thinking....That's a good idea Paul. You got me thinking...John Seymourhttps://www.blogger.com/profile/11350487038873935295noreply@blogger.comtag:blogger.com,1999:blog-1840985738235902482.post-87648575891746235162012-12-18T10:56:30.985-05:002012-12-18T10:56:30.985-05:00How about a piece on ink density in litho (offset ...How about a piece on ink density in litho (offset printing)?! Why simply increasing the density might not necessarily increase the image quality. (And yes, that leaves us with the fact that the ink layer in offset, especially for cmy, is quite thin, semi transparent).Anonymoushttps://www.blogger.com/profile/04096598783871940756noreply@blogger.comtag:blogger.com,1999:blog-1840985738235902482.post-82242256099463947412012-11-10T11:10:36.820-05:002012-11-10T11:10:36.820-05:00Thank you, Paul, for the kind words and the idea f...Thank you, Paul, for the kind words and the idea for a blog. I'm still composting the idea in my head... What level would you like to see: <br /><br />a) (Entry level) A blog post about red, green, and blue light, the difference between additive and subtractive primaries, and why paint differs from ink.<br /><br />b) (Moderate level) Journeys on a Photon Wing... following the path of a photon when it encounters ink.<br /><br />c) (Advanced) The whole Kubelka Munk schtick, with the climax showing what a little bit of turbidity does to your printing gamut. John Seymourhttps://www.blogger.com/profile/11350487038873935295noreply@blogger.comtag:blogger.com,1999:blog-1840985738235902482.post-4815265226453744462012-11-10T05:50:42.195-05:002012-11-10T05:50:42.195-05:00Very interesting. It great because it is putting f...Very interesting. It great because it is putting figures to effects I am seeing and reading most weeks. One thing, what about the issue of ink transparency in relation to CMYK overprint colours? Any thing re this and the facts in the blog?<br /><br />Paul SherfieldAnonymoushttps://www.blogger.com/profile/16664050046899682091noreply@blogger.comtag:blogger.com,1999:blog-1840985738235902482.post-25725922448815528342012-10-24T10:20:46.012-04:002012-10-24T10:20:46.012-04:00Thanks John,
I think we can certainly conclude th...Thanks John,<br /><br />I think we can certainly conclude that the absorption is (one of) the key factors in lightfastness: cyan ink is less vulnerable than magenta. A small research with yellow ink showed me that the thicker layer is a bit more lightfast, this would explain the light scattering issue. Further I expect some testing of UV and HUV-inks on lightfastness in the near future, hope to see some results there.<br /><br />Regards,<br /><br />Fons Fons Puthttps://www.blogger.com/profile/03301254141981454590noreply@blogger.comtag:blogger.com,1999:blog-1840985738235902482.post-22536114459491249232012-10-23T12:09:01.220-04:002012-10-23T12:09:01.220-04:00Thank you, Fons.
Let me start with a few caveats....Thank you, Fons.<br /><br />Let me start with a few caveats. First, "Flies walk on the ceiling." This is the mantra that I cite when I catch myself pontificating about stuff where I have no direct knowledge. This idea was explained in my first blog post:<br />http://johnthemathguy.blogspot.com/2012/06/flies-walk-on-ceiling.html<br /><br />Second caveat, I have no data to support any of the opinions I am about to share. "In God we trust, all others must provide data." (Deming)<br /><br />With that said, here are my learned opinions.<br /><br />The amount of UV light (which breaks down pigments) that hits a given square centimeter of surface is the same, so I would expect the lightfastness of the ink to not change with ink film thickness.<br /><br />The amount of pigment breakdown depends upon the amount of UV light that is absorbed by the pigment. The more absorption, the more breakdown. If the color (spectra) of the inks are somewhat the same, I would expect that the absorbance would be similar. One would expect that HUV inks must have a similar color.<br /><br />On the other hand, the critical part is the absorbance in the UV, and not the "color". I have seen some spectral curves of inks in the 300 nm to 400 nm range, and I know enough to know that the absorbance is weird... it can't be inferred from the spectra in the visible range.<br /><br />On the other hand, I know nothing about the UV absorption of HUV inks, so I really shouldn't comment. <br /><br />On the other hand, I understand that HUV inks dry by using a UV band that is tuned to something in the ink - which I read to mean there is something in the ink that readily absorbs UV. This could lead to pigment breakdown, if the pigments are what is doing the absorbing. Or, it could lead to solvent evaporation, if the solvent is doing the absorbing.<br /><br />On the other hand, the ink below the surface is (to some extent) hidden by light scattered in the ink above. This suggests to me that a thicker ink might be somewhat more lightfast, at least to the extent that light is scattered in the ink. <br /><br />On the other hand, traditional ink films of ~1 micron are already pretty darn thin and (at least for traditional CMY inks) they are designed to be as transparent as possible, so this might not be a big effect.<br /><br />On the other hand, some pigments are more lightfast than others. I overheard someone in an elevator say that they thought they heard someone in a subway say that one popular yellow pigment is much more lightfast than the other popular one. <br /><br />I am certain that my comments have made the answer very clear! a) John has a lot of hands, b) John is ignorant of a lot of stuff, and b) it is a complicated issue and depends on which effect is predominant.John Seymourhttps://www.blogger.com/profile/11350487038873935295noreply@blogger.comtag:blogger.com,1999:blog-1840985738235902482.post-57507541925329268342012-10-23T10:09:55.542-04:002012-10-23T10:09:55.542-04:00Congratulations with this fine blog. Do you think ...Congratulations with this fine blog. Do you think a thicker layer of ink will also cause a higher lightfastness? This would imply that processes based on thin ink layers (Benny Landa, HUV - inks) are more vulnerable to UV-radiation than classic offset ink.<br /><br />Fons Put<br /><br />Fons Puthttps://www.blogger.com/profile/03301254141981454590noreply@blogger.comtag:blogger.com,1999:blog-1840985738235902482.post-7021087420631789512012-10-07T16:24:56.270-04:002012-10-07T16:24:56.270-04:00Dr. Vigg - I think there might be a typo in your n...Dr. Vigg - I think there might be a typo in your numbers. You went from 190 to 190?? And then changed to 290 - which is a different color altogether. John Seymourhttps://www.blogger.com/profile/11350487038873935295noreply@blogger.comtag:blogger.com,1999:blog-1840985738235902482.post-12193414879985091182012-10-07T16:23:10.892-04:002012-10-07T16:23:10.892-04:00Danny - Do you happen to have the spectrum of a gr...Danny - Do you happen to have the spectrum of a green Easter egg? It's all in the name of science. Good connection, Danny.John Seymourhttps://www.blogger.com/profile/11350487038873935295noreply@blogger.comtag:blogger.com,1999:blog-1840985738235902482.post-51787151748793613912012-10-07T08:57:48.344-04:002012-10-07T08:57:48.344-04:00John, the phenomenon of which you write here is n...John, the phenomenon of which you write here is not limited to printing ink and has been given the name "dye dichroism". Think about yor younger days preparing Easter eggs. The vegtable dyes in the cups look to be the wrong colors, as you have described, "pink" looks red, "yellow" looks red, "blue" looks indigo or navy, and "green" looks ... hmm ... What color does green become? Try your spectral test and seeifbyou can predict that one !<br /><br />DannyUnknownhttps://www.blogger.com/profile/03791815228024493846noreply@blogger.comtag:blogger.com,1999:blog-1840985738235902482.post-29426227151333325672012-09-27T18:47:28.032-04:002012-09-27T18:47:28.032-04:00Great post, John.
Speaking of ink in the can, I w...Great post, John.<br /><br />Speaking of ink in the can, I was having some difficulty with Pantone 190. I eventually solved them, however, when I switched to Pantone 190. My ink rep assured me that, unlike the 190, the 290 was guaranteed to not turn pink in the can.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-1840985738235902482.post-85051432332334641412012-09-27T15:49:32.222-04:002012-09-27T15:49:32.222-04:00Thank you, Steve! I appreciate the kind words, an...Thank you, Steve! I appreciate the kind words, and I am glad that people find a bit of entertainment in the blog. <br /><br />I miss those days, also. But I suspect the memory of them is more fun than they actually were.<br /><br />BTW - I don't understand everything I write, either.John Seymourhttps://www.blogger.com/profile/11350487038873935295noreply@blogger.comtag:blogger.com,1999:blog-1840985738235902482.post-74648650112918539812012-09-27T13:24:33.441-04:002012-09-27T13:24:33.441-04:00I assure you, John, that not only have I looked at...I assure you, John, that not only have I looked at the really cool pictures, but I have also read each of your blog posts (and have recommended them to friends). I can't say that I understand all of them, but I enjoy reading them. Takes me back to our days back in the skunkworks.Steve Tesmerhttps://www.blogger.com/profile/04595487880736056406noreply@blogger.com