Details, details, details ...

Started Oct 4, 2013 | Discussions thread
John King
John King Forum Pro • Posts: 14,941
Re: Regarding monitors, etc ...

bobn2 wrote:

John King wrote:

bobn2 wrote:

John King wrote:

Big Ga wrote:

John King wrote:

There is the further wrinkle demonstrated in the images above, that not all monitors are:

1) Calibrated (actually, it is the video card that's calibrated, in almost all cases ... )

Note - the above information is incorrect.

Note - It might appearto be "incorrect" to those not completely familiar with the entire process/es that computers use to display graphic images; and how colour management works .

My monitor calibration is pretty basic, and involves setting up the monitor controls on the monitor. I know that this just affects the monitor, because the electronic link (VGA, DVI or HDMI) doesn't have a provision for the monitor to program the display card. I'd be very grateful to know of a better technique, please.

When an appropriate monitor (one with an EDID chip) is connected to a modern video card with either a dual-DVI cable or, more commonly these days, an HDMI cable, the graphics card queries the EDID chip in order to ascertain what the monitor wants as input from the graphics card. Bit depth, etc.

Any kind of spider works by its software injecting known (Pantone?) colour numbers into the graphics card, then measuring what the monitor displays (via a USB port). The calibration device software then adjusts the (basically uncalibrated) graphics card LUT to output the "right" colour numbers so that the monitor displays a set of colour numbers for each pixel that corresponds to the pre-calibrated colours supplied by colour spider, whatever brand it happens to be.

As Boggis rightly stated, one needs a much more expensive and different version of these devices to change the colour LUT in a printer, monitor or scanner. One also needs to know precisely what one is doing before making modifications to these devices.

Since most high quality monitors come with a factory calibrated colour LUT, as do high quality printers and scanners, it is best that one leaves them alone, and concentrates on getting the un-calibrated part in tune with the rest of the system/workflow which is already well calibrated.

Thanks for that. I found details of EDID here.

You are welcome, and thanks for that further reference.

I have a number of references relating to the EDID/monitor relationship. It is discussed elsewhere on Wikipedia as well (under DVI, HDMI as well as other places, IIRC). I can probably ferret some out for you, if you would like me to. It's also quite interesting how far its history goes back. I don't recall any of the other articles that I have read mentioning how long a history the EDID has (in technology terms ... ).

Also interesting that it is so dependent on the method of connection between the graphics card and monitor. I was originally using dual-DVI, but switched to HDMI. Both allow the card and EDID chip in the monitor to communicate. Most other connection methods do not (e.g. single channel DVI does not).

If the card cannot communicate with the EDID, it effectively limits the data path to 8 bit only. There are probably other limitations as well. If you know of any, please inform me. That level of practical knowledge (to me ... ) is very useful.

Presumably the process we are talking about is the CIE xy co-ordinates in bytes 25-34 and the additional white point descriptor (if used).

Now you've lost me.

I have a reasonable understanding of how these things work, but leave the fine details to those who understand them at a professional level. Like editing files using a hex editor - I can do it, and have done it, but only when there was no other possible method of rectification of the problem.

I tend towards assuming that the people who do these things know what they are doing. Seiko-Epson got some US university research unit to reformulate their inks and write a new colour LUT for their Rx880 series printers. I suggest that they probably did this because they could not do it themselves ...

OTOH, you arean expert in such things, and they are part and parcel of your 'stock in trade'. So I will leave that part of it to you .

As long as it works properly for me at a practical level, that's as far as I tend to take my own research and understanding of the guts of these things. Sometimes that can be a long way ... .

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