Because of money. Times when a usual desktop printer has a better embedded computer than the general-purpose desktop computer driving it are long gone and the process of actually getting the data in format which will be displayed by a computer to a format suitable for printing is quite complex. Also as time passes, expectations of users about the complexity of image to be printed and quality of the print itself increase.
There is need for corporate secrecy because today one of the most important parts of a modern printer is how it actually processes data on the host computer. Just like we had hardware fax modems and then switched to software ones which are cheaper, today we're in age of "software" printers (some call them "winprinters" because they usually only have drivers for Windows) that do all of the data processing for the printer on the host computer and then send data in a proprietary and closed format to the printer. The printer will have hardware optimized for that particular format and since printers are made in large volumes, the custom hardware will be cheap. The embedded computer in printer will then convert the data sent to it by the personal computer to something it can actually print. Since, as I said, we already have optimized formats and hardware (and firmware) which is made to work nicely with them, the hardware itself can be cheaper and can quickly process the data that needs to be printed. This way for example a printer which has only say 16 MiB of RAM can work with large photos that themselves are much larger than its own RAM.
Companies themselves make money by selling printer supplies and by licensing the printer components. This way, they benefit from secrecy because there would be no reason license use of hardware if all implementation data is free.
Also the idea you proposed here is quite reasonable and back in the days of expensive printers, we've had printers that can directly print pages in PostScript and PCL. Such printers didn't need any special drivers at all. Today such printers are rare and are mostly big stationary units size of pieces of furniture. So while currently used printing technologies usually aren't very new (usually computerized xerography or inkjet), the technologies for cheap low quantity printing are developing quickly and are new.
UPDATE I did notice that that some manufacturers like for example Brother or OKI do have relatively cheap printers that do support common page description languages and may not need some special proprietary drivers.
thanks for your answer! <br/> What do you mean by "the technologies for cheap low quantity printing [...] are new" ? Is there something more than inkjet technology in printers ? Or is inkjet more complicated than what I think ? – Gael Lorieul – 2011-11-27T14:09:17.630
@Galdor No, I mean that while the printing process exists for quite some time, the way printers are implementing the process keeps changing little by little. At first, the main goal of printer manufacturers was to actually get a printer working with a reasonable price tag. FOr example in that period on some printers you had to choose if you want to have color printing or black and white. The change was done by swapping cartridges. After that the focus was on quality for some time for you had all those "photo" printers with even more colors – AndrejaKo – 2011-11-27T16:35:44.483
@Galdor Then we've had all-in-one craze with everyone wanting to have printer, scanner, fax and whatnot in one device. And now it seems that for a while we're having the price craze. Also every printing process now in use (with exception of dot-matrix) is extremely complicated. Dot-matrix is "just" complicated. Every little print head on an inkjet printer is a work of art in itself. Ten years ago an inkjet cartridge of good quality cost as much as a cheap printer costs today in a store. All this needs research and development. – AndrejaKo – 2011-11-27T16:43:46.273
Sorry for my late answer. – Gael Lorieul – 2011-12-03T13:52:47.250
Sorry for my late answer. <br/> I think I got your point. Let me say it my way to make sure I got the thing right : host computer driver optimisation = cheaper printer hardware parts = more profit. And thus, there is a need of secrecy as you were talking about, and as a consequence no generic driver. – Gael Lorieul – 2011-12-03T14:10:10.070
However, HPLIP project is openSource, so does that mean that HP considers that, since 2006 (i.e. launching year of the HPLIP project), the printing technology is no longer worth of being kept secret ? Is HP the only corporation to have such a point of view on things or is it the start of a more general change in printer companies strategy ? And thus, do you think we will soon have a generic printer driver ? – Gael Lorieul – 2011-12-03T14:10:58.273
@Galdor I don't see much change. Read this page and this page. Note the binary plug-in. I for example had a printer which heavily relied on host data processing (LaserJet 2600n) and it for example requires the non-free plugin to work. On the other hand many printers made by HP also use PCL, which is public. SO basically you have the free code for PCL, which isn't new and you have binary plug-ins for printers which work the way I described.
– AndrejaKo – 2011-12-03T15:34:02.123@Galdor Also that same HP licenses Canon's print engines and it could be that the proprietary information isn't their to release. Also after doing some research, I found that there are companies which make relatively cheap printers that work with well-known printing standards. For example many Brother printers work fine with just generic PCL drivers. It seems that OKI too has some not too expensive printers which work with PCL and PostScript. So, yes, there appears to be some change towards use of more open standards. – AndrejaKo – 2011-12-03T15:39:10.343
1thanks for your answers !<br/>I get it now !<br/>I hope printers will be using open printing standarts one day. – Gael Lorieul – 2011-12-04T15:13:30.720