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RE: [hpoj-devel] Revised "gamma.ps info" + screenshot
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From: Salkind, L. <Lou...@de...> - 2000-09-20 13:36:01
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I finally got to install 0.6 last night. RedHat 6.2 / Officejet 720. Everything installed perfectly. To test the colors, I started applying various gamma corrections as suggested by Joe. The good news is that the colors are much better than they used to be. I suspect this has a lot to do with the fact that I installed a new ink cartridge before testing, but also because I have slightly different parameters to cdj550. Like Joe, I found that gamma.ps was needed. Following the instructions on http://graphics.stanford.edu/~ericv/gamma/gamma.html, I determined that the best gamma for the OfficeJet 720 was about 1 / .475. In other words, instead of using .333 as Joe did, I used .475 instead. The colors were still a bit off, though. In particular, the blue, cyan, and pink all looked a bit dark and possibly not quite the right color on a test color strip (the Redhat print page). I'm pretty sure gamma isn't helping here, because the colors are being requested to be displayed at full intensity. What is needed is a slightly more sophisticated transformation. Being curious, I tracked down some more web references and learned a bit more about gamma, color management, etc. If other (non-color experts) are curious, I found the Charles Poynton FAQs to have a wealth of information: http://www.inforamp.net/~poynton/GammaFAQ.html http://www.inforamp.net/~poynton/ColorFAQ.html I also found several web papers on how people in practice get the colors right, e.g. http://www-ise.stanford.edu/class/psych221/00/ben/ http://www.tsi.enst.fr/~hardeber/work/CIC1996_faxcolor/node5.html the gimp manual, chapter 14 To make a long story short, it seems as though the procedure for calibrating a printer/scanner device as follows: a) obtain a high quality hard-copy print of known colors b) scan these colors in with the scanner and compare the colors we think we got to what we were expecting c) compute the transformation function f required to normalize the scanner input d) print out a known test pattern on the printer e) rescan in the test pattern and compare what we got to what we were expecting f) compute the transformation function h = g(f) required to normalize the combination of the scanned printed image input g) compute the transformation function g = h(inverse(f)) to get the correction to apply in the postscript file I'm now tracking down references on what people typically use for the form of these transformation functions. It seems as though the colors are transformed from either RGB or CMYK to CIE, which corresponds in a more linear way to how humans can differentiate colors. Then, a non-linear least squres regression is applied to get the best fit between the input colors and the measured colors. I'm actually game to try this type of procedure some time once the scanning support for the 720 is in place. In the meantime, though, I'll live with slightly weird color printing. Lou -----Original Message----- From: pa...@rc... [mailto:pa...@rc...] Sent: Tuesday, September 19, 2000 5:33 AM To: hpo...@li... Cc: pa...@rc... Subject: Re: [hpoj-devel] Revised "gamma.ps info" + screenshot > I'm attaching a text file that contains a revised and augmented version o= > f the > "gamma.ps info" that I posted earlier to the hpoj-devel mailing list. It = > needed > a little correction and more information. Please add to your docs if you = > choose. Hi, Joe. Thank you very much for the updated information. I will see about putting it into a future version of the software. Lou, does this updated information help you any? > According to your hpoj "TODO" list you are planning to expand the xojpane= > l app. > I don't really know how much functionality the hpoj project will eventual= > ly > have, but I'm assuming that some day there might be a need for a GUI. > > Needing something new to learn, I slapped together the beginning of a Qt = > - > based GUI that could serve as a main window for a "hpoj control" front en= > d. It > builds and runs with no problems. It was done with the new Qt designer an= > d > Gimp.=20 Thanks for putting this together. That's a really cute picture! However, a printer with its tongue sticking out isn't quite the emotion I wanted to convey here. :-) I haven't done a lot of serious thinking on the matter yet, but basically my vision was to have a list of attached devices (which would probably be only one for most people, but many for me:-) on the left side (for example, mlc:mlcpp0, hpjd:my-jdex.my-domain.com:1, etc.), and when you clicked on one you would get a bunch of tabbed dialog boxes in the remainder of the window, which would provide various status information and control options for the selected device. To list some possibilities by tab: - general -- device's model name and number, and a summary of its capabilities (print, scan, fax send, fax receive, copy, etc.). An option to test communication with the device (via the MLC echo channel). - status -- LCD contents (if available), and other general status info that can be gathered via PML (online, offline, errors, etc.). - print -- ink/toner levels, buttons to print various test pages and initiate print cartridge alignment and cleaning operations. - print queue -- to check on status of lpd print queue, cancel jobs, etc. - scan -- buttons to launch various SANE frontends (xscanimage, xsane), since there's no reason to re-invent the wheel. - copy -- set options (copy count, color/b&w, image enhancement, special features), start copy button. Maybe options to assist the user with advanced copying operations, such as double-sided copying. Maybe somehow take advantage of a duplex unit on the G series (if installed). - fax configuration -- numerous options here (local phone number and station name, dial-out access code, beep and volume options, country, blacklist management, flash/line type, ring/answer/redial/forward options, dial mode, speed dials, fax send/receive modes, etc.). - fax status -- view/clear fax log of device and/or system. Presumably fax send/receive would be handled externally. Fax send could be handled by lpd queues, and fax receive could be done either manually from SANE or automatically from some daemon, which could e-mail you the fax images. - maybe some "geek options", for example to play around with PML: probe for supported PML objects and display current values, get/set specific PML objects, etc. Did I say I haven't thought about this very much? :-) In any case, this is a lot of functionality, and it would be a good idea to start small. I also still need to try to get specs on some things, like how to determine ink/toner levels and clean/align cartridges. Does anyone have ideas to add to this wishlist for xojpanel-on-steroids? David _______________________________________________ hpoj-devel mailing list hpo...@li... http://lists.sourceforge.net/mailman/listinfo/hpoj-devel |
