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ADC Callibration - Quick question

post #1 of 13
Thread Starter 
I have a very quick questions:

- When i use your ADC callibration disk and use a 16-235 pattern i get an ADC RESULT 132-70. If i use AVS709 in White clipping i'm only get whites up to 235 "blinking".

- If i make my ADC RESULT to 0-255 my ADC RESULT is 128-50 and i get ALL whites up to 252 "blinking".

Which is best?, am i loosing detail if i use 16-235? (in movies and videogames).

Thank you very much.
post #2 of 13
Thread Starter 
nobody?
post #3 of 13
No, there "Should" be NO content in video over 235. However, sometimes it get in there..
My BRP is set to Video and only puts out up to 235. My Cable box is set to YCbCr not RGB so I am only getting 16-235.. My projector is set to YCbCr and only displaying 16-235.. It is a point people will argue about. Should I leave head room (see up to 255) or maximize contrast ration (nothing over 235). If you want to use the full range, you will want all your input devices set to provide that same full range as setting brightness and contrast for full range RBG vs YCbCr may be 2 different settings. Also with using the full range, you set the contrast to anywhere between 235 and 255 then switch back to YCbcr if your devices are not all RGB .. I don't think Contrast will be effected like brightness is when you switch between the 2 settings. Other may be able to say for certain. I think a lot of it depends on the device..
Edited by airscapes - 4/18/13 at 5:58am
post #4 of 13
Greetings

Just a bit of a correction ... It is not true that there should be no content above 235.

There is a mandatory range for content ... and there is a legal range ... think optional. Film makers can choose to have content that goes up to around 254 if they want ... it is allowed. Some films have stuff that goes all the way, some half way, some not at all. Problem is ... the BD box does not exactly tell you which film uses this range and which does not. Just like they don't tell you what gamma the film is mastered at.

So to be safe, we want to see the video range up to 109% when we can.

A scene done with the full range can look very different when you limit it to just 100%.

Regards
post #5 of 13
Thanks Michael, can you tell us in your experience if you set contrast with Full range (RGB) and then switch back to limited (YCbCr) does the change effect the contrast like it can the brightness? Or does the change in brightness only happen if the there is a problem with the input or display device?
Edited by airscapes - 4/18/13 at 7:46am
post #6 of 13
Quote:
Originally Posted by airscapes View Post

No, there "Should" be NO content in video over 235.

That's not actually what some of the most knowledgeable people in the industry say when I talk to them. At SMPTE, HPA and NAB I routinely had the top engineers come into our booth and ask about head room, if we calibrate it and are pleased to hear that we do calibrate it and recommend preserving it as default in our workflows.

The headroom is used sparingly, for thing like specular highlights, but it is suppose to be there and can be used.
post #7 of 13
Greetings

Doug,

We try to follow the 3 rules for setting contrast and if we do, then we protect for the full range.

1. No clipping
2. No discoloration/color shifting
3. Eye fatigue considerations

The exception comes in when dealing with certain brands of TVs let's say. Say you want to get your TV certified for good housekeeping. But in the process of the certification, it is determined that your TV cannot display the full range to 254 ... unless you lower the contrast (light output) so much that it violates another one of the requirements. Minimum light output requirements. So what can you do? Well you have to go back and re-engineer the TV so that it does meet the requirements. Lots more money and time consuming.

So an exception is made for you because you have been a good partner over the years. They allow you to get away with displaying only up to 245 or so ... half way in this optional range ... but you can meet the light output requirements at that setting level. So here is the thinking that goes into this ... without being an apologist. The 4 most important things to image quality. Remember that list?

1. Black levels
2. Dynamic Range (Contrast Ratio)
3. Accurate Color
4. Detail/Resolution

Dynamic range rates higher than detail/resolution. So in this case where you will compromise, you give up a little on the detail side to preserve the dynamic range of the image. Because lost dynamic range is visible on all content and losing a bit of detail is not usually noticed at all especially if you don't know you are missing it in the first place and only a portion of the movies out there actually have content in that area anyway.

This explanation is not an invitation to arbitrarily cut everything off at 235. It is not up to us to decide what is important in a picture and what is not. It is merely a description of the thinking process involved when a compromise has to be made for any number of reasons. This is an issue often found on the Plasma TV side ... and such trade offs are rarely considered for other technologies. We don't automatically go for higher CR numbers either because there is a limit to human vision and if the TV exceeds what the eyes are capable of, it becomes a waste as well.

Regards
post #8 of 13
Thanks Michael!
My previous question still is unanswered and maybe I did not phrase it well enough or it could just be something funky with my projector.

If I set my output on my input device to 4:2:2 I do not see WTW or BTB
So I set the Brightness using the pattern and 0 DLP dithering at video black to verify.

Now I switch the input device to RBG and can see WTW an BLB and and the previous brightness setting is off by 6 or 7 clicks

I have never bothered to look at contrast as the change in the low end was so drastic and I have a device that does not provide full range so I don't want to calibrate using the RGB output.

Would you expect to see the same changes in the upper end, which would invalidate switching to RGB color space to set the contrast then back to 4:2:2
Is this just a bad implementation of the electrics in the projector or something one would expect on any set?

Hope that makes sense
post #9 of 13
Greetings

I'd pick the setting that showed me the whole range and I would go from there. The settings like 444 422 and rgb are misrepresented so much on so many devices that I don't trust anything on the face of it. So if it doesn't show the whole range ... then I am onto the next setting to see if that one will. Then I calibrate in that setting. So what if the brightness now has to be -6 versus 0 in the other setting. It doesn't matter. smile.gif There is nothing here that would de-stabilize the display and cause it to burn your house down.

There are so many combinations of tvs and BD players and cable boxes out there. So you optimize to your best source ... and then if the cable box is off WRT brightness, then you set up another memory somewhere to account for it.

Don't fixate over a word ... since there is nothing inherently right or wrong here anyway ... just find the one that shows the whole range and begin there.

Regards
post #10 of 13
Quote:
Originally Posted by Michael TLV View Post


So an exception is made for you because you have been a good partner over the years. They allow you to get away with displaying only up to 245 or so ... half way in this optional range ... but you can meet the light output requirements at that setting level. So here is the thinking that goes into this ... without being an apologist. The 4 most important things to image quality. Remember that list?

1. Black levels
2. Dynamic Range (Contrast Ratio)
3. Accurate Color
4. Detail/Resolution

Here ya go, Michael, straight from the book....

post #11 of 13
Thanks, that makes sense to me!
post #12 of 13
My adc results are113,145. Most other people's are around 130,70 why so different?...Am I better too use around 130,70? Do my adc numbers make rgb or ycc better?
rolleyes.gif
Edited by Vic12345 - 4/20/13 at 10:15pm
post #13 of 13
Quote:
Originally Posted by Michael TLV View Post

A scene done with the full range can look very different when you limit it to just 100%.

I've never seen a comparison of the sort where the difference was that obvious, only statements of the sort.

In fact, the examples I've seen show minimal differences at best and the content above 235 needs to be highlighted in pink or green to be noticeable in any significant way. Also, it's usually just specular highlights and nothing more.

So, while it's technically correct to show up to 109% and wrong to limit things to 100%, I've never seen much benefit to doing so from a real world, practical perspective that involves watching a lot a BD or DVD content.


Do you have a A/B image comparison to share that shows the kind of difference you're talking about? A picture is worth a thousand words.
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