Spears & Munsil HD Benchmark Blu-Ray 2nd Edition - Page 23 - AVS Forum
Forum Jump: 
Reply
 
Thread Tools
post #661 of 671 Old 07-14-2014, 01:01 PM
AVS Special Member
 
dmunsil's Avatar
 
Join Date: Mar 2000
Location: Kirkland, WA, USA
Posts: 1,078
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 24
Quote:
Originally Posted by AustinJerry View Post
The blue filter method is a relic from the CRT days, so that folks without colour testing gear could try and approximate what the correct colour was supposed to be. But if you have calibration gear then it's completely unnecessary, because you've got a totally objective means of setting the colour, as opposed to the subjective (it's relying on your eyes' sensitivity to colour) blue filter method. If you're setting colour by eye, you're throwing your calibration out of the window

The blue-only mode is extremely accurate, and does not rely on your eyes' color sensitivity; it couldn't, because the image is monochromatic. The test relies on your eyes' sensitivity to small brightness differences, which works great. If the blue filter works for your display (i.e. it cuts out the red and green and you don't have wide-gamut display with an active CMS), then it's also quite accurate; more than accurate enough to be used by professionals. It's also fast and has very few gotchas. It's definitely the go-to way to adjust color and tint for displays that it works for. Using instruments is much slower.

With a colorimeter, you have the problem that some of them are really inaccurate with light sources with spiky spectra, and that sadly describes a lot of modern display technologies. So it's very possible to get a worse calibration with a colorimeter, if it can't read your display accurately.

Spectroradiometers (and good colorimeters) can read a display fine, but there is still some math to do to duplicate the blue-filter approach.

For Color, you read XYZ (in linear, non-normalized values) for white, red, green and blue (using windows, if possible, rather than just aiming at the patches on a color bar pattern). You adjust Color until Yblue = Ywhite - (Ygreen + Yred). Every time you adjust Color, you have to re-measure all four windows. When everything is right, the same equations should match for X and Z. If they don't come at least close, there's something wrong, probably a CMS or your colorimeter can't measure your display accurately.

For Tint, you measure red, green, cyan, and magenta, and adjust Tint until (Ycyan - Ygreen) = (Ymagenta - Yred). Again, every time you adjust the Tint control you have to re-measure all four colors. And again, once Y matches that should also be true for X and Z. If they aren't close, something is wrong.
StevenPK likes this.
dmunsil is offline  
Sponsored Links
Advertisement
 
post #662 of 671 Old 07-14-2014, 01:10 PM
AVS Special Member
 
AustinJerry's Avatar
 
Join Date: Jan 2003
Location: Austin, Texas
Posts: 6,811
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 224 Post(s)
Liked: 646
Thanks for the replies, Don and Stacy. For the time being, since the 3X blue filter results in "close" to black, and since the results I get when I use the blue-filter approach are visually stunning, I think my best bet is to assume the calibration is good enough. All other measurements (grayscale, gamma) are excellent, so there is no reason for me not to sit back and enjoy the PQ.
AustinJerry is offline  
post #663 of 671 Old 07-20-2014, 09:54 PM
AVS Special Member
 
p5browne's Avatar
 
Join Date: Jun 2008
Location: Sudbury, Ontario, CANADA
Posts: 3,756
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 41 Post(s)
Liked: 167
I've found after a `close as possible calibration to spec', checking with the filter, it says Colour and Tint aren't set right - which one is right, and which one is wrong? I'll stick to the calibrated by Meter results. VQs recommend setting Colour and Tint to Midpoints and let the VQ take care of the rest. So unless your set has serious issues, I'll stick with this guideline.
p5browne is offline  
post #664 of 671 Old 07-21-2014, 08:58 AM
Senior Member
 
AV_mike's Avatar
 
Join Date: May 2009
Posts: 260
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 5 Post(s)
Liked: 35
Quote:
Originally Posted by p5browne View Post
I've found after a `close as possible calibration to spec', checking with the filter, it says Colour and Tint aren't set right - which one is right, and which one is wrong? I'll stick to the calibrated by Meter results. VQs recommend setting Colour and Tint to Midpoints and let the VQ take care of the rest. So unless your set has serious issues, I'll stick with this guideline.
I'm sure Don or Stacey will correct me if I've got this wrong, but with regards to the use of the filters:-
If your display/projector is natively 'wide gamut' and uses an internal (factory adjusted, probably non-accessable) CMS in order to approximate to the required Rec. 709 colour gamaut, then the Blue Filter method of setting colour and tint will not give good results. This is due to blue actually containing varying amount of red and green in order to give the correct xy coordinates, therefore a blue filter will now remove those reg/green additions giving the incorrect luminance to the 'remaining blue'. Also this explains why the 'other' colour bars do not go black when using the filter, they probably also contain some blue (that the filter will NOT remove), due to the internal CMS also adjusting their coordinates.

The bottom line is - if you've got a meter - use it, if you don't have a meter - the filters are better than nothing.

Regards, Mike.
AV_mike is offline  
post #665 of 671 Old 07-21-2014, 10:17 PM
AVS Special Member
 
Doug Blackburn's Avatar
 
Join Date: May 2008
Location: San Francisco - East Bay area
Posts: 3,453
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 18 Post(s)
Liked: 206
Using filters to set color and tint is only a tiny bit better than nothing. If nothing is "0" and using a great $25K spectro meter is a "10" the filters are about 0.5.


The issues with filters not working ideally are even more complex than the previous post indicated. The filter and phosphor (CRT/plasma) or internal color filters (LCD) have to have very similar spectral content... contamination with red and green to get accurate Rec 709 color is one way there can be a mismatch but even if your TV allows you to turn off red and green completely (some TVs and projectors have that feature), if the spectral distribution of the blue light from the TV or projector is different than the spectral properties of the filter, you can still have errors.


Every written instruction I've ever seen for using a blue filter (haven't read S&M's blurb yet though) ALWAYS says near the end of the explanation of how to use the filters (something like this): When you are done setting the color and tint controls, view a variety of video content and if color or tint does not look ideal, adjust by eye until you get the color and tint controls set correctly." So even the instructions are essentially telling you that what you see should be the final check and you may (make that "almost certainly will"0 have to do final adjustments by eye after using the filter. So why not just adjust by eye in the first place? Why bother with the filter if it's not going to work right 95% of the time (it has been my experience that I have had to readjust by eye about 95% of the time after using a filter).


These days I almost always leave the controls at their defaults and take care of everything that needs to be taken care of using a meter. With 1 exception... color controls don't always work the same way in different models or brands of TV. I've seen color controls that adjust saturation. I've seen color controls that adjust color luminance. I've seen color controls that affect both luminance and saturation and not necessarily equally for each "click" of the control in 1 direction or the other. BUT if the color control DOES affect saturation and the mode you'd most like to use for calibration happens to have 1 or more primaries undersaturated, you MIGHT be able to use the color control to move the undersaturated primaries back out so it or they are no longer undersaturated. Most CMS controls won't let you add saturation beyond your starting point. So if your starting point is inside the Rec709 triangle, if you are hoping for a good calibration, keep your fingers crossed that you can bump the Color control up a bit to get your undersaturated primary back to the point of NOT being undersaturated. Once you have all the primaries' saturations at or outside the Rec709 triangle, you tan then use the CMS controls to fine-tune each of the primary and complimentary colors.


If your initial measurements indicate your color saturation is good, you can just leave the Color control alone. But if the primaries are undersaturated, it's time to cross your fingers and see what the Color control does -- never assume it works some specific way that's common to all TVs or projectors, because that's not likely to happen any time soon. You always have to assume you don't really know what the Color (and Tint) controls do until you measure them. And you must be using software that shows saturation, luminance, and hue for each color so you can see which of the 3 factors changes as you increase or decrease the Color control.


Of course, if you measure the primaries and all of them are at saturation or were a little oversaturated, the CMS controls should be able to resolve that--- if the CMS controls work well. Which brings us to another problem... CMS controls don't always work right. I've seen Color controls CHANGE what they are doing as you look at each "click" in the adjustment range.
ConnecTEDDD likes this.

"Movies is magic..." Van Dyke Parks
THX Certified Professional Video Calibration
ISF -- HAA -- www.dBtheatrical.com
Widescreen Review -- Home Theater & Sound
Doug Blackburn is offline  
post #666 of 671 Old 07-21-2014, 10:20 PM
AVS Special Member
 
sotti's Avatar
 
Join Date: Aug 2004
Location: Seattle, WA
Posts: 6,585
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 12 Post(s)
Liked: 164
Quote:
Originally Posted by AV_mike View Post

The bottom line is - if you've got a meter - use it, if you don't have a meter - the filters are better than nothing.

Regards, Mike.
This is actually my opinion, and likely a summary of what Doug was saying as well:

The bottom line is - if you've got a meter - use it, if you don't have a meter - the filters maybe worse than nothing.
ConnecTEDDD likes this.

Joel Barsotti
SpectraCal
CalMAN Lead Developer
sotti is offline  
post #667 of 671 Old Yesterday, 11:16 AM
AVS Special Member
 
sspears's Avatar
 
Join Date: Feb 1999
Location: Sammamish, WA, USA
Posts: 5,226
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Liked: 41
I agree with Doug and Joel.


Joel, you should post a step-by-step article on using CalMAN and a meter to set color and tint. Maybe you already have one.
mcjimsey and ConnecTEDDD like this.
sspears is offline  
post #668 of 671 Old Yesterday, 11:25 AM
AVS Special Member
 
AustinJerry's Avatar
 
Join Date: Jan 2003
Location: Austin, Texas
Posts: 6,811
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 224 Post(s)
Liked: 646
Yes, Joel, that would be very useful to us CalMAN users!
AustinJerry is offline  
post #669 of 671 Old Yesterday, 10:13 PM
AVS Special Member
 
KC-Technerd's Avatar
 
Join Date: Jan 2004
Location: Liberty, MO
Posts: 1,298
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 8 Post(s)
Liked: 95
Quote:
Originally Posted by Doug Blackburn View Post
...but even if your TV allows you to turn off red and green completely (some TVs and projectors have that feature), if the spectral distribution of the blue light from the TV or projector is different than the spectral properties of the filter, you can still have errors.
I'm a bit confused by this, as it seems to imply that you would both turn off the red and green elements (electron guns, LCD sub-pixels, etc.) and use the blue filter. Why would you want or need to do both? For color (when using the blue only or blue filter method) we are attempting to match the luminance of the blue element in blue with the luminance of the blue element in white. For hue we are attempting to match the luminance of the blue element in cyan with the luminance of the blue element in magenta. In order to do these we have to eliminate the light output from the red and green elements so we only observe the blue. Turning off the red and green elements should be a totally effective way of doing this, where the filter is an attempt to block the light output of these elements which probably is going to be something less than 100% effective. Both turning off the red and green elements and using the blue filter is redundant.

Yes, there are numerous potential issues. Unless the color decoder is 100% accurate, color and hue adjustments will need to be performed for red and green as well as blue. The blue only method also assumes that primary color elements are to rec. 709 standards. As A/V_mike mentioned, I believe a wide-gamut color system, such as x.v.Color on a Sony TV, would likely produce inaccurate results with the blue only method. With an accurate color decoder and accurate primaries (normal gamut) the blue only method should be extremely accurate, as Don said.

Last edited by KC-Technerd; Yesterday at 10:17 PM.
KC-Technerd is offline  
post #670 of 671 Old Yesterday, 10:43 PM
AVS Special Member
 
Doug Blackburn's Avatar
 
Join Date: May 2008
Location: San Francisco - East Bay area
Posts: 3,453
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 18 Post(s)
Liked: 206
Quote:
Originally Posted by KC-Technerd View Post
I'm a bit confused by this, as it seems to imply that you would both turn off the red and green elements (electron guns, LCD sub-pixels, etc.) and use the blue filter.

OY! Brain fart... out of my ever lovin' mind! Blue filter on the brain!


Of course if you turn off red and green, you adjust without needing a filter and that solves the entire problem of the filter and the blue light source not matching, spectrally. Blue only modes are more likely to be useful than the blue filter but you can't even bank on that, you still have to view content for a while (days) to see if everything "seems right" (lacking a meter of course).

"Movies is magic..." Van Dyke Parks
THX Certified Professional Video Calibration
ISF -- HAA -- www.dBtheatrical.com
Widescreen Review -- Home Theater & Sound
Doug Blackburn is offline  
post #671 of 671 Old Yesterday, 11:43 PM - Thread Starter
AVS Special Member
 
ConnecTEDDD's Avatar
 
Join Date: Sep 2010
Location: Athens, Greece
Posts: 2,168
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 41 Post(s)
Liked: 421
Quote:
Originally Posted by KC-Technerd View Post
I believe a wide-gamut color system, such as x.v.Color on a Sony TV, would likely produce inaccurate results with the blue only method. With an accurate color decoder and accurate primaries (normal gamut) the blue only method should be extremely accurate, as Don said.
Hi, xv.Color is not enabled to the display when you are watching a pattern from any calibration disk because the calibration disk patterns haven't encoded with xv.color flag.

Ted's LightSpace CMS Calibration Disk Free Version for Free Calibration Software: LightSpace DPS + CalMAN ColorChecker
S/W: LightSpace CMS, SpaceMan ICC, SpaceMatch DCM, CalMAN 5, CalMAN RGB, ChromaPure, CalPC, ControlCAL
Meters: JETI Specbos 1211, Klein K-10A, i1PRO2, i1PRO, SpectraCAL C6, i1D3, C5
ConnecTEDDD is online now  
Reply Display Calibration

Tags
Spears Munsil , Spears Munsil High Definition Benchmark Blu Ray Disc Edition Blu Ray , Spears Munsil Hd Benchmark And Calibration Disc 2nd Edition
Gear in this thread

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page


Forum Jump: 

Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off