APL, windows and greyscale measurement

lemurios

Novice Member
Dear All,

Once again I need your help!

I calibrated my Panasonic st60, using APL patterns (from AVSHD). Once I finished the calibration I noticed that black images (e.g. ending credits of a film) have slightly reddish color. During the calibration I increased the Red-Cutoff from 0 to +1. Therefore, by reducing it back to zero the redish tint disappears.

However, I didn't want to change my calibration settings so I re-measured the greyscale. I did the exercise twice using the first time the APL patterns and the second time normal windows. The results are quite different and I am wondering why. Is there a pattern that I can "trust" more? I bear in mind the ABL, but can this really be the reason of such big difference for greyscale adjustments?

Thanks a lot for your help!


Note: The first screenshot is with normal window, the second with APL.

white.PNG
white apl.PNG
 

AndreiNR

Well-known Member
Honestly that's a question many if us have been asking to others and ourselves and there's simply no straight answer. You can find on the avsforum many pages of discussions and no final result. I recommend you to read Michael Chen's article about abl vs normal windows.
What I can suggest you is to do two separate calibrations one with 10% windows and another with small apl windows. Then look at a grayscale ramp. Then some actual content. You may find that the actual differnces are small.
Regarding the red tint you have two options:
1- calibrate using 10% ire wb advanced adjustment to bring red and blue to the same level at 5% and do a compromise in the actual 10% white wb
2- do a full wb calibration using 5% and 80-100% ire and then asjust the midlevels with 10p. This might m e the worse out of two because you might get the 20-30-40... points right but heavy differences in the ones between them(15-25..)
I have to tell you that in my oppinion the 50" models are a pain in thw arse regarding calibration.
Have you updated to the latest firmware?
 

lemurios

Novice Member
Thank you for your reply and your advices!

Indeed I've read few discussions and they seem to be inconclusive. I will try the first option regarding the red tint. My tv is panasonic p42st60 and the I have the latest software. Although I am novice to calibration, I should admit that it is interesting!
 

-Hitman-

Well-known Member
Actually you need to experiment to find the ideal pattern size that gives you the image your after, older plasma's had a less aggressive ABL and so I recommend a normal window pattern but still experimentation is required to find the best size to suit the particular display model and size, APL are newer forms of pattern source and are recommended for newer/recent displays due to the changes in ABL and power restrictions.

Regarding your red tint, it could be a limitation of your sensor (what model and age?) as it's at the lower end of the GS and this is where most sensors struggle and if it's an older colorimeter, these drift ~12 months old, I'd recommend the i1D3 for this purpose as it's great for GS calibration inc low end and has sealed optics so won't drift quickly, otherwise your trusting an inaccurate meter or trying blindly.

HTH.
 
Last edited:

Patrik G

Banned
During the calibration I increased the Red-Cutoff from 0 to +1. Therefore, by reducing it back to zero the redish tint disappears.
i think you need to check black clipping also
it sounds like they are clipping to low.
i guess you have to lower all RGBs not just RED-Cutoff
or you need to adjust Brightness.
 

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