AVS Forum banner
Status
Not open for further replies.
1 - 20 of 23 Posts

·
Registered
Joined
·
22 Posts
Discussion Starter · #1 ·
Has anyone tried calibrating their projector with Colorvision's Spyder2PROâ„¢ Studio? Would mounting the spider on a tripod part way between the projector and screen provide enough light to do the calibration?


For those using an HTPC it would seem that you could set the projector on something close to the color temp, grayscale and gamma you desire and then bring it in with a generated PC profile.

http://www.colorvision.com/profis/pr...iew.jsp?id=341
 

·
Registered
Joined
·
5,001 Posts
The Spyder2PRO will provide you raw xyY data, but to do anything with it, you need either or both of a) software, and b) an understanding of color science. The point at which you are "close", you might as well go alll the way, since you have presumably been following calibration procedures to that point.
 

·
Registered
Joined
·
22 Posts
Discussion Starter · #3 ·
Possibly it is not obvious that the analysis software that comes with this device calculates a precise monitor profile and updates the graphics card configuration with it. No understanding of color space is required. Since the projected image is a combination of the graphics card monitor profile and projector setup this should be better than what a typical individual can achieve by eye.


I know for a fact that it is for direct view monitors but I'm not sure if this also would apply to projectors.
 

·
Registered
Joined
·
5,001 Posts
It applies to any display. However, the graphics card has a lot more control over the display via analog (voltage "tweaks" have meaning) versus DVI (where you have to change whole quantization values). Having used the Spyder2 on my LCD that's fed via DVI, the results were not good. Instead, I used some of the techniques found in this forum to set-up the display.


BTW, I have 2 Spyder2's.
 

·
Registered
Joined
·
5,001 Posts
Jeff - Did you create an ICC profile, or just calibrate them? Also, how are the PCs fed, analog or digital?


Later,

Bill
 

·
Premium Member
Joined
·
10,415 Posts
Bill,


I calibrated the PC's with an ICC profile because that was all that was available to me with my Apple LCD monitor and Laptop monitors. These profiles were significantly better using my Eye-One Pro than my old Monaco EZColor. The other LCD displays were calibrated with my software using the Pro.
 

·
Registered
Joined
·
5,001 Posts
Laptops are a special case since the LVDS signal is different than DVI (the graphics subsection controls the display more directly). The LCD monitor is probably the true contrary case to my experience. I may have to give it a try again with some of the newer toys I have.


Later,

Bill
 

·
Registered
Joined
·
341 Posts
The Spyder2 with Optical works well for me with my CRT front projector. I make a icm profile and use it to get the grayscale under control. Just aim it at the screen from about eight inches and make sure that it is angled a bit to mostly miss it's own shadow.


Charlie
 

·
Registered
Joined
·
5,001 Posts
Scott,

That update will be released soon, and with the right math, you can do FP calibrations. I, personally, am less interested in ICC/ICM profiles than in a proper calibration.


Later,

Bill
 

·
Registered
Joined
·
201 Posts
One thing apparently missed in this thread is that the Spyder allows real-time manual calibration of the display itself.


Sure, you can use it to modify the video card output to suit the desired profile, but you can also run a "Precal" applet that allows you to adjust the grayscale of the display device and see the results in realtime. In fact, you should do that even if you're going to modify the video card output, since you can get closer that way (that's why it's called Precal).


Also, I'm not sure what the gobbledygook was about 'quantization values' in DVI. There is absolutely no difference in calibrating DVI versus analog from a computer video card standpoint. Everything is digital in the card's memory, where the calibration offset is applied. In one case, the RAMDAC converts that to analog; in the other case, it's sent to a DVI transceiver. In either case, it's still 8 bits per pixel in RGB.


If you have, say, a CRT RPTV with a DVI input, the only difference between connecting a computer video card through analog or digital is where the D/A conversion takes place -- on the video card, or in the RPTV's chassis.


KC
 

·
Registered
Joined
·
341 Posts
KC,


Precal does't actually do the grayscale measurements. It is used to set the black reference plus the white reference luminance and color temperature (D65) before doing the grayscale calibration with Optical. The black reference target is at level 18 since Precal is not usually used in a dark environment. It is easy to substitute a suitable black reference target however.


Well said on the DVI vs. analog video levels mis-understanding. Some folks haven't yet realized that each digital video level has a corresponding analog voltage so there is no practical difference between analog and digiatal interfaces from that standpoint - they both have the same quantization.


Charlie
 

·
Registered
Joined
·
11,213 Posts
And that quantization is why the display's greyscale controls should be used rather than profiling the monitor on the computer. These controls adjust the actual digital panel with more bits than 8, or the actual voltages on the CRT.
 

·
Registered
Joined
·
341 Posts
krasmuzik,


With an analog projector using a truly analog adjustment scheme you can set a particular video level to any voltage value you want within design parameters. Unfortunately (for your theory anyway) the next level (and all others) changes in voltage with respect to the first one so the voltage difference between the levels remains almost the same. Just think of an escalator in a department store. Each stair is roughly the same height and is analogous to adjacent analog or digital video levels. With the escalator turned off all the stairs are in a fixed position. If you forced the escalator to move ahead three inches then all the stairs would be in a different position (higher for example) but the height between the stairs would be the same. The height of the stairs in this analogy is related to the difference in luminance from one adjacent video level to the next. Human vision is not sensitive to absolute luminance (you can't use a human for an accurate light meter) but it is fairly sensitive to relative luminance. Human vision would adapt to the slight increase or decrease in absolute luminance average of all the stairs very rapidly. Couple this with the fact that the difference in adjacent video levels was purposely picked to be near the limit of the ability of human vision to discriminate and you have a case where it takes really special circumstances for humans to discriminate between adjacent video levels much less be able to see half level rounding errors on the fly!


As an aside - my EH8000 uses digitally controlled voltage multiplier chips to control all crt adjustments. The change in crt drive, G2, brightness or contrast of one step is quite visible. In my EH8000 most of the digital controls have about 100 steps (the drive and G22 have more I think) end to end which is less than the number of video levels in a computer monitor (256) or TV (254). The only time it is an issue is when I try to adjust the crt drives to hit D65 exactly. For it to be as good as it gets (temperture-wise) I have to use a icm profile.


Rant section - should be skipped by children! :)


I don't suppose this will change the way you feel but just for the record - I have been using icm profiling for the last 18 months and have yet to see any increase in banding even using even using static ramp greyscale test patterns. Not only that but my EH8000 has a near perfect greyscale even though it has no blue gamma circuit. Without profiling I would have mid-level blue cast with blue OK near the white reference and the black reference. Many times I have read that my projector is a good one to have except for the out of control blue crt. There is no blue hump with profiling. I can use a sensitive gamma checker like the AIM one with near perfect result. Only at the darkest few levels is there any color tinge.


If your interested you might just give the AIM gamma checker a try to see how good your greyscale at gamma 2.5 is. The AIM Color Dither Calibration Target is linked on this page. http://www.aim-dtp.net/aim/calibration/index.htm


Charlie
 

·
Registered
Joined
·
5,001 Posts
Quote:
Originally Posted by scottyb
In laymans term, can I calibrate my projector's grayscale with this unit and the new software coming out?


Scott
Scott - Yes, but you need a model into which to plug the xyY data. The PRO gives you gamma curves (and an editor for use with a profile), but to really get color balance correct, etc., you need a model of some sort. Also, get the SpyderTV if you are needing it soon, or the PRO v2.0 when it comes out. I would not risk buying the PRO for HT use on the off chance you got the older sensor.


Charlie - I respect your opinion, but the difference between line voltage and what a projector does with it can diverge - especially once you turn the contrast or brightness knobs away from their "neutral" values. This is where your escalator theory begins to fall apart (the steps at the top get taller with contrast turned up - to a point - and then shrink). In the analog domain, partial steps have meaning. How much meaning can vary by signal type (e.g., 8-bit YCrCb 4:2:2 is roughly equivalent to 10-bit RGB, 4:4:4 is 11-bit, IIRC), but they all have meaning. Run a quick calculation of a classic IRE grayscale (in 10 IRE increments) vs. the equivalent digital RGB values and you will see what I mean.
 

·
Premium Member
Joined
·
10,415 Posts
I don't see why a model is required if xyY data is available to calibrate gray scale.


I would target 0.3127 in x and 0.3290 for y from 0 to 100 percent on gray windows. As long as you understand y is mostly green and x is mostly blue and red you can get this correct without a model. Using an RGB display is a nice crutch, but not a requirement. You won't have a good idea of how far off you are or were without a Delta E calculation, but you can get it done with only xy data. Whether it is correct is more a function of technique, the display and the instrument than any model.


Gamma is pretty simple to calculate. Here is a link to the formula.

http://www.poynton.com/notes/colour_...mma_correction


You can also calculate color values of interest using the calculator and equations found here. I personally am a fan of Delta E CMC if you wish to use a color matching function.

http://www.brucelindbloom.com/index.html?Equations.html
 

·
Registered
Joined
·
5,001 Posts
Jeff - One might observe that once one is calculating gamma, one is technically using a model... ;)
 

·
Premium Member
Joined
·
10,415 Posts
Quote:
Originally Posted by Ursa
Jeff - One might observe that once one is calculating gamma, one is technically using a model... ;)
I agree. The question, however, was, "In laymans term, can I calibrate my projector's grayscale with this unit and the new software coming out?". I don't believe a gamma model is required to calibrate color, but I did add the gamma model because I believe that is a requirement for an accurate calibration. When I discuss gray scale I am only referring to color. Others may see this differently.
 
1 - 20 of 23 Posts
Status
Not open for further replies.
Top