Spears & Munsil HD Benchmark Blu-Ray 2nd Edition - Page 23 - AVS Forum
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Old 07-14-2014, 02:01 PM
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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.
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Old 07-14-2014, 02:10 PM
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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.
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Old 07-20-2014, 10:54 PM
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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.
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Old 07-21-2014, 09:58 AM
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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.
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Old 07-21-2014, 11:17 PM
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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.
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Old 07-21-2014, 11:20 PM
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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.
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Old 07-22-2014, 12:16 PM
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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.
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Old 07-22-2014, 12:25 PM
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Yes, Joel, that would be very useful to us CalMAN users!
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Old 07-22-2014, 11:13 PM
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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.

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Old 07-22-2014, 11:43 PM
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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).

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Old 07-23-2014, 12:43 AM - Thread Starter
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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.

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Old 07-23-2014, 06:19 AM
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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.
Yes, I agree 100% and did not intend to imply that x.v.Color would be enabled when using test patterns for adjusting color and hue. Assuming my understanding is correct, the potential issue is that a display with x.v.Color is using primary elements that are more saturated than rec. 709 standard. This is to make the display x.v.Color CAPABLE. In order to reproduce only the rec. 709 color gamut the extended gamut display must always be mixing the primary colors to some degree. For example to reproduce a fully saturated rec. 709 blue, the display's color management system will have to add some illumination of the red and green elements to the illumination of the blue element in order to desaturate the blue from its native blue point to the rec. 709 blue point. If only the blue element is illuminated, the result will be outside the rec. 709 color gamut. On a standard gamut display, only the blue element would be illuminated in order to reproduce a fully saturated rec. 709 blue.
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Old 07-23-2014, 10:40 AM - Thread Starter
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Originally Posted by KC-Technerd View Post
Yes, I agree 100% and did not intend to imply that x.v.Color would be enabled when using test patterns for adjusting color and hue. Assuming my understanding is correct, the potential issue is that a display with x.v.Color is using primary elements that are more saturated than rec. 709 standard. This is to make the display x.v.Color CAPABLE. In order to reproduce only the rec. 709 color gamut the extended gamut display must always be mixing the primary colors to some degree. For example to reproduce a fully saturated rec. 709 blue, the display's color management system will have to add some illumination of the red and green elements to the illumination of the blue element in order to desaturate the blue from its native blue point to the rec. 709 blue point. If only the blue element is illuminated, the result will be outside the rec. 709 color gamut. On a standard gamut display, only the blue element would be illuminated in order to reproduce a fully saturated rec. 709 blue.

Hi, It's better to keep that xy.Color spec out of this discusion, it's better to say that we have a wide gamut display (larger from rec709).

xy.Color capable displays doesn't mean that it has wide gamut also, just that they can encode that signal information for YCC values out of the 16-240 range (236-255 etc.) from a xv.Color capable player with xv.Color encoded content.

Modern consumer displays are coming with oversaturated green/red most of the times, and undersaturated blue, so any internal display CMS adjustment will make the blu-filter to not work.

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Old 07-23-2014, 11:27 AM
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Hi, It's better to keep that xy.Color spec out of this discusion, it's better to say that we have a wide gamut display (larger from rec709).

xy.Color capable displays doesn't mean that it has wide gamut also, just that they can encode that signal information for YCC values out of the 16-240 range (236-255 etc.) from a xv.Color capable player with xv.Color encoded content.

Modern consumer displays are coming with oversaturated green/red most of the times, and undersaturated blue, so any internal display CMS adjustment will make the blu-filter to not work.
I simply was using x.v.Color (or xvYCC) as an example of a wide gamut display because that is what I have. My understanding is that a display being x.v.Color capable requires that it be a wide gamut display. What would be the point of a display recognizing the x.v.Color flag and decoding the x.v.Color metadata if it can't display any of the colors represented by that metadata? Excluding UHDTV, is there currently any system for home video other than x.v.Color (xvYCC) that actually makes use of a larger than rec. 709 gamut?

I would also think that if a display truly has an undersaturated blue primary element, that no CMS adjustment would be able to correct it back to rec. 709 blue. The most saturated blue the display will be able to produce will be by illumination of the blue element only. Adding red and green illumination can only reduce the saturation of blue.
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Old 07-23-2014, 11:41 AM - Thread Starter
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Originally Posted by KC-Technerd View Post
I simply was using x.v.Color (or xvYCC) as an example of a wide gamut display because that is what I have. My understanding is that a display being x.v.Color capable requires that it be a wide gamut display. What would be the point of a display recognizing the x.v.Color flag and decoding the x.v.Color metadata if it can't display any of the colors represented by that metadata?
xv.Color movies are only some ''Mastered In 4K'' Blu-Ray Movies Disks and some demonstration disks from Display Companies, pure marketing stuff, just to impress with over-saturated colors at stores.

Blu-Ray Movies (1080p) or any available movie content that is available right now @ UHD resolution (Sony/LG/Samsung) is following the REC.709 color space also and it's has 8-bit color depth per color channel and same chroma subsampling (4:2:0) like bluray movies.
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Old 07-26-2014, 02:13 PM
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Originally Posted by Doug Blackburn View Post
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.

I agree as far as the total calibration of color. For just setting Color and Tint, the filter can work very well on many displays. As you say, just setting Color and Tint doesn't get you very far.

Quote:
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.

The spectral curve of the blue filter doesn't actually need to match the spectral curve of the blue phosphors at all (and in practice it never does). It just needs to be appropriately selective, in that it cuts out enough of the red and green to enable you to get an accurate calibration. In practice it needs to attenuate red and green by around 5000x the amount of attenuation of blue. That's hard to do with a "gel" style filter. We use Lee Tokyo Blue, which is the most selective blue filter you can get for reasonable sums of money, and even then most TVs require two or three thicknesses of gel to get the filter to be selective enough to cut out all the green. And some can't cut out the green at all, which makes the filter basically useless. Our advice to people in that situation is not to use the filter, which we think is the right answer.


There are three big issues that can make a blue filter not work well.


1. wide-gamut displays with a CMS
2. green light (and maybe even red) leaking through the filter
3. deliberately (or inadvertently) incorrect color decoder coefficients (the infamous "red push")


There are plenty of displays that have one or another of these issues, but there are also plenty of displays that don't have these issues, especially if you put them in their "cinema" mode or whatever they call their closest-to-correct mode, where they turn off a lot of the torch-mode stuff. If your display doesn't have these issues, then using a blue filter to set the Color and Tint controls is fine. It works. In practice, if you find that factory mode has Tint off by more than a notch or two, you're probably dealing with a much larger problem than you can fix with those controls. But Color, specifically, is often set too high out of the factory, even in "cinema" modes, and a blue filter can help you turn that down to a correct level.


Obviously getting proper color on a display involves much more than setting Color and Tint, and to do almost anything other than just get those set absolutely requires a colorimeter or spectroradiometer, and no one is pretending otherwise.
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Old 07-26-2014, 05:53 PM
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VQs

VQ Manufacturers and Distributors recommend leaving Color and Tint to them (In other words, Mid Point, Zero or what ever is the Default - just NOT Dynamic!) - except in extreme conditions. Spears and Munsil Blu-ray 2 is your next choice if not using the VQ and/or Meter and Calibrating Equipment. If you insist on using the other guys Blu-ray: hint, Basic usually gives a closer to spec result than the Advanced.
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Old 07-26-2014, 06:16 PM
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^ What is a "VQ"?
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Old 07-26-2014, 08:38 PM
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^ What is a "VQ"?
Video Equalizers - Lumagen Radiances, iScan Duos, etc
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Old 07-29-2014, 12:11 PM
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I have a question regarding bit depth! I might have asked this already i can't remember so forgive me if i did!
I have an xbox one (36 bit depth) and a PS4 both are outputting at 12bit. I also have my Sony 6200 Bluray set at 16bit.
My display is the new Sony w/ the Trilouminus tech so I get a beautifully saturated colors.
Are the colors being supersampled, if thats the correct word? Does that skew the PQ?
Would I be getting a more accurate PQ by setting everything to 24bit?
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Old 07-29-2014, 01:10 PM
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I have an xbox one (36 bit depth) and a PS4 both are outputting at 12bit. I also have my Sony 6200 Bluray set at 16bit.
My display is the new Sony w/ the Trilouminus tech so I get a beautifully saturated colors.
Are the colors being supersampled, if thats the correct word? Does that skew the PQ?
Would I be getting a more accurate PQ by setting everything to 24bit?

Bit depth has nothing to do with color saturation. Extra bit depth reduces banding artifacts. Your XBox might be generating game images at higher than 8-bits per pixel - many games now use 16-32 bit floating point for at least their final rendering surfaces. But commercial video/film content is all delivered at 8 bit. So higher bit depths are only useful from a delivery box if the box is applying its own video processing that involves interpolation of levels. Your boxes might be doing that kind of thing; hard to say.


Ultimately the only way to know would be to put up images that tend to show banding, like light cyan skies, smoky dark rooms, and wide expanses of smooth fleshtones. (I'm not going to comment on what movies have wide expanses of smooth fleshtones... ). Put the device in question in the lowest bitdepth, wait until you see some banding, then switch bit depths and see if the banding goes away.


You could try the same thing with some XBox games - play the game and look for banding in the sky. When you see some, switch bit depths and see what happens.


My prediction, for what it's worth, is that most of the time the banding won't go away, because it's probably in the source. Most banding seems to be caused by bit starvation in the compressor. But I could be surprised; you might find some useful differences.
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Old 07-29-2014, 01:44 PM
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We might see some content delivered as 10-bit before the end of the year using HEVC.

On the Xbox One, 8-bit RGB is delivered to the HDMI transmitter. If you are outputting 36-bit, it is padded with zeros just before output. No actual processing is done at >8-bit. Xbox One's Blu-ray player is a matter of convenience only. A standalone Blu-ray player is better. I worked on the Xbox One, so I know the internals of the entire video pipeline.
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Last edited by sspears; 07-29-2014 at 01:48 PM.
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Old 07-29-2014, 01:48 PM
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Out of curiosity, how many would be interested in watching a documentary on display calibration? It may go further into video quality. It will cover on-set -> post -> home video transfer -> home calibration. Possibly audio and streaming as well. This is a personal project that I am starting this year. It will probably take two years to complete given my schedule. I will interview Joe Kane, Joel Silver, Charles Poynton, SpectraCal, and many more. I will probably create a FB page for it, once started, and post stills along the way.


It will be shot in 6k on the Red Dragon using the Zeiss Otus 85mm f/1.4 lens as the primary lens for the interviews. I am using the Arri L7-C and Arri L5-C for lighting. On the audio side I will be using Sound Devices 633 recorder with Schoeps CMIT5U shotgun mic.
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Old 07-29-2014, 01:54 PM
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Some displays turn off even more processing if you change the label of the input. We had some LGs at work that worked better if you changed the label to PC. This is even after you turn off all of the extra processing. Renaming the input to PC turned off even more. Not sure how many displays are like this, but thought I would pass along.
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Old 07-29-2014, 02:19 PM
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Quote:
Originally Posted by sspears View Post
Some displays turn off even more processing if you change the label of the input. We had some LGs at work that worked better if you changed the label to PC. This is even after you turn off all of the extra processing. Renaming the input to PC turned off even more. Not sure how many displays are like this, but thought I would pass along.
Yes, there's also a few Samsungs that do this too.
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Old 07-29-2014, 02:36 PM
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Out of curiosity, how many would be interested in watching a documentary on display calibration?
Count me among those who would be interested!
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Old 07-29-2014, 02:48 PM
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Originally Posted by sspears View Post
Some displays turn off even more processing if you change the label of the input. We had some LGs at work that worked better if you changed the label to PC. This is even after you turn off all of the extra processing. Renaming the input to PC turned off even more. Not sure how many displays are like this, but thought I would pass along.
The cheap 39" 4k Seiki I use as a PC monitor has a significant improvement in color gamut accuracy before calibration if you send it 12 bit 422 (from a Radiance) vs. RGB which would be 8 bit. Also, the is a very visible improvement in the number of color shades in 4k or higher photos with 10 or 12 bit vs. 8 bit. Supposedly the TV is native 8 bit dithered to 10 bit.
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Old 07-30-2014, 01:05 PM
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Quote:
Originally Posted by sspears View Post
Out of curiosity, how many would be interested in watching a documentary on display calibration? It may go further into video quality. It will cover on-set -> post -> home video transfer -> home calibration. Possibly audio and streaming as well. This is a personal project that I am starting this year. It will probably take two years to complete given my schedule. I will interview Joe Kane, Joel Silver, Charles Poynton, SpectraCal, and many more. I will probably create a FB page for it, once started, and post stills along the way.


It will be shot in 6k on the Red Dragon using the Zeiss Otus 85mm f/1.4 lens as the primary lens for the interviews. I am using the Arri L7-C and Arri L5-C for lighting. On the audio side I will be using Sound Devices 633 recorder with Schoeps CMIT5U shotgun mic.
I, for one, am interested as long as the information is "technical". By that, I mean, no interviews of people giving the history of tv standards, how they got interested in the topic, etc..
I just want specific info of what to look for in test patterns, how to adjust things correctly and so forth. BTW-I do have, and use, your recent BR disc for my equipment. I like it a lot. I just want more technical info (perhaps videos also) about display calibration. Thanks for all the work you have done on your present disc.
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Old 07-30-2014, 04:57 PM
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I, for one, am interested as long as the information is "technical". By that, I mean, no interviews of people giving the history of tv standards, how they got interested in the topic, etc..
I just want specific info of what to look for in test patterns, how to adjust things correctly and so forth. BTW-I do have, and use, your recent BR disc for my equipment. I like it a lot. I just want more technical info (perhaps videos also) about display calibration. Thanks for all the work you have done on your present disc.
It sounds like you want a tutorial, not a documentary.
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Old 07-30-2014, 04:59 PM
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Or at least an advanced tutorial.


The doc will be more what and why. Not so much in the how.


What types of advanced videos or articles would you like to see?
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