Hughes: Introducing the ColorHug open source colorimeter
Hughes: Introducing the ColorHug open source colorimeter
Posted Nov 16, 2011 1:13 UTC (Wed) by ringerc (subscriber, #3071)Parent article: Hughes: Introducing the ColorHug open source colorimeter
Unless you do accurate colour work, you don't. If you do accurate colour work, though, it's vital.
A quick and dirty FAQ about colorimeters and calibration in general (rather than this one in particular):
Q: "My monitor already comes with a profile, so why should I create one?"
A: Actually, at best your monitor comes with a profile that was vaguely appropriate for the model when it was first produced. It doesn't come with a profile for your particular panel as each individual panel and backlight is different. If your monitor isn't brand new the profile is out of date because the panel's colour changes as it ages. In any case, unless you have a high end professional colour panel it's likely that the profile that came with it is completely bogus or is just a dummy sRGB profile that's effectively a no-op.
Q: "My monitor has an sRGB mode, so why can't I just use a regular sRGB profile and avoid having to calibrate?"
A: The sRGB mode in your monitor is incredibly unlikely to have been measured and calibrated during production. It'll be a generic set of settings for the entire production run. Even if yours is one of the high end panels where the sRGB mode was actually calibrated for each individual panel during production, it's out of date now as the monitor has aged. Worse, sRGB was designed for CRTs so it has a narrow gamut that's inappropriate for LCDs and restricts the colours that can be displayed.
Q: "Can I use this to calibrate printers and scanners too?"
A(1): For printers you need a spectrophotometer. They're expensive, like $lots, because they require precision calibration during production, fancy emissive light sources, and more. Try to find a ColorMunki or a 2/h i1Pro but if it's an older instrument be prepared to pay to have it recalibrated.
A(2): For scanners you can get a cheap but excellent quality IT8 target from Wolf Faust (http://targets.coloraid.de/), scan it, and calibrate using Argyll CMS, VueScan, or your vendor scanner software if it isn't totally crap. I cannot recommend Wolf's targets enough.
Posted Nov 18, 2011 13:39 UTC (Fri)
by dafid_b (guest, #67424)
[Link] (2 responses)
First some background: I have a student artist partner, who was introduced to colour profiles for printers etc last year. I have read a very little in the popular press about colour profiles and a tiny amount in programming APIs about colour gamuts - so am not an expert in any way!
Between us we have three monitors, a scanner, a couple of digital cameras, a couple of light sources (sun-light photo lamps) and a photo-printer which we use with cheap paper, quality paper, cheap ink and photo ink.
We could get some IT8 targets, thanks for that link:), and could calculate profiles for the scanner and cameras as described.
However, could the ColorHug and spectrophotometer be replaced by a process like the following?
1.a) Scan the IT8 target image
[1? Is variation in sunlight due to weather, season, or pollution something that can be corrected for? For important events, today's sunlight could be used as a prediction for tomorrows sunlight:)]
Then process the results and make colour profiles for these combinations.
2) print the target image on quality paper
Then scan and photograph the output of the printer using the calibrated camera and scanner...
3.(a...g) calibrate all the input devices using the printed output
4) print the target image on cheap paper
Then scan and photograph the output of the printer using the calibrated camera and scanner...
5.(a...g) calibrate all the input devices using the printed output
(and etc for the cheap ink and other variations)
For the monitors...
1) Display the reference image.
The above sounds complicated, and laborious. However it provides colour profiles for most of the anticipated uses for the many devices - and the user can choose which combinations make sense for their use of the devices. As such it seems like a reasonable approach.
The 'A calibrates B which calibrates C' would introduce errors, but because of the large number of devices used, the mess of cross-measurements would provide opportunities for error minimisation or correction that would counter these introduced errors - another task for software.
Also, there are comments above about the 'colour profile' of a monitor changing with age, placement in a room and the lighting that surrounds it. I think the photo of the image can capture these impacts - whereas the ColorHug might not be able to?
It would be nice to have a midday profile, an afternoon profile and a night profile for the monitors and also sunlight, fluorescent and incandescent viewing profiles for the print-outs - although this is more about an integrated colour management facility in the desktop than about how to obtain a colour profile...
Thanks for reading so far, looking forward to any comments!
Posted Nov 20, 2011 12:20 UTC (Sun)
by ringerc (subscriber, #3071)
[Link]
There are several problems with this. One is multiplication of error - deltaE is greatly increased by "chaining" profile production like this, greatly reducing the quality of the resulting profile.
If the gamut of the intermediary device (in this example a scanner) doesn't wholly encompass the gamut of the device being profiled then you'll have no useful data for the areas where the intermediary can't capture the profiled device's output. For example, your profile might not think your printer can to bright orange because the scanner can't capture bright orange so the bright orange swatches in the printout looked reddy-brown instead and the profile generator considered them out of gamut.
Perhaps more importantly, the devices don't always use the same colour models - for example, an RGB scanner might be being used to profile a printer that uses CMYK inks. That'll make it really hard to get a good profile and will require different logic in the profiling software to make a profile that's actually useful with the output device.
Overall, it's an OK-ish way to make rough profiles of devices if you don't have any better options, but there are plenty of reasons it's a crap way to do profiling and not generally recommended.
Posted Nov 24, 2011 13:13 UTC (Thu)
by gwg (guest, #20811)
[Link]
You can certainly try this camera or scanner type of approach out
Hughes: Introducing the ColorHug open source colorimeter
1.b) Take a photo of the target image under photo-light-a with camera-a
1.c) Take a photo of the target image under photo-light-a with camera-b
1.d) Take a photo of the target image under photo-light-b with camera-a
1.e) Take a photo of the target image under photo-light-b with camera-b
1.f) Take a photo of the target image under sun-light(1?) with camera-a
1.g) Take a photo of the target image under sun-light with camera-b
2) Take long exposure (to average out any flickering) with each digital camera
3) Calculate profiles
With the application of some automation it should not be too difficult to manage.
Hughes: Introducing the ColorHug open source colorimeter
Hughes: Introducing the ColorHug open source colorimeter
it isn't a colorimeter. Typically such devices have spectral
sensitivities that are noticeably different to the human eye,
hence their measurement of color doesn't match what we see very well.
A color measurement instrument on the other hand is designed to emulate
the spectral sensitivities of the human eye, and it's success at this
is a measure of such an instruments quality (and cost!).
if you like (see <http://www.argyllcms.com/doc/Scenarios.html#PP4>),
but the chances are that you will be disappointed in the
result.