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Green Y value different based on input
Using Color HCFR on my display, I used the same source (HD DVD player w/HD test disc) and measured the component input as compared to the DVI input. The results are below.
Comp DVI
40% gray 18.97 14.16
80% gray 91.19 62.48
red x 0.663 0.654
red y 0.341 0.346
red Y 18.13 15.08
grn x 0.287 0.286
grn y 0.613 0.613
grn Y 51.49 24.58
blu x 0.147 0.148
blu y 0.059 0.064
blu Y 5.255 4.197
The picture appears much darker over DVI, which can be see in the gray numbers I provided. But what is causing the huge difference in green Y and what does it mean? Is that just the difference in picture brightness/luminance again or is there a color issue between the two inputs?
Comp DVI
40% gray 18.97 14.16
80% gray 91.19 62.48
red x 0.663 0.654
red y 0.341 0.346
red Y 18.13 15.08
grn x 0.287 0.286
grn y 0.613 0.613
grn Y 51.49 24.58
blu x 0.147 0.148
blu y 0.059 0.064
blu Y 5.255 4.197
The picture appears much darker over DVI, which can be see in the gray numbers I provided. But what is causing the huge difference in green Y and what does it mean? Is that just the difference in picture brightness/luminance again or is there a color issue between the two inputs?
1 - 14 of 14 Posts
Not surprising at all.
Each input will need different calibrations.
Each input will need different calibrations.
It is to my understanding that Y is luminance. Green is the dominant wavelength that has the most effect on overall picture brightness, therefore, a separate channel for green primary is not needed since it is included in Y. That explains why the lower Y values over DVI are darker.
NOLA, you're mixing apples and oranges.
By the time primetimeguy is making measurements off the screen all of the decoding has happened. He is measuring "pure" RGB signals, mixed accordingly for the colour being displayed.
It's simply that each input type will translate what they receive on their inputs to a specific brightness on the screen and as such the display settings for brightness, contrast, etc. will need to be set differently for each input.
By the time primetimeguy is making measurements off the screen all of the decoding has happened. He is measuring "pure" RGB signals, mixed accordingly for the colour being displayed.
It's simply that each input type will translate what they receive on their inputs to a specific brightness on the screen and as such the display settings for brightness, contrast, etc. will need to be set differently for each input.
Thanks for the input guys. I figured I'd need different calibrations between inputs. But I was wondering if this difference would should up as a difference in viewed color, or is the difference in green luminance just because of the lower "brightness" I see in the picture. If so this can be fixed by brightness and contrast adjustments rather than having to tweak the green color only.
It might be a little of both. The only way to know for sure is to measure them both.
Sorry, I don't follow. Both what, and how? I've shown my color measurements as well as a couple gray scale numbers.
Quote:
Originally Posted by jvincent /forum/post/12849317
It might be a little of both. The only way to know for sure is to measure them both.
Sorry, I don't follow. Both what, and how? I've shown my color measurements as well as a couple gray scale numbers.
Component is, by definition, YPbPr so the TV will need to do a colour decode operation to generate the RGB values that the set displays.
The DVI connection can either send digital RGB, in which case the colour decoding is done in the player, or it can send YCbCr which means the colour decoding will happen at the set.
If you send RGB it is entirely possible, in fact I would say probable, that the decoding will be slightly different, which would make the values you measure different even if you have the same luminance for 100% white.
Even if you send YCbCr there's no guarantee that the digital decode will be the same as the analog one.
The DVI connection can either send digital RGB, in which case the colour decoding is done in the player, or it can send YCbCr which means the colour decoding will happen at the set.
If you send RGB it is entirely possible, in fact I would say probable, that the decoding will be slightly different, which would make the values you measure different even if you have the same luminance for 100% white.
Even if you send YCbCr there's no guarantee that the digital decode will be the same as the analog one.
I thought DVI was always RGB, but HDMI could be either?
I will have to try getting both inputs to have the same 100% luminance and then check the green. Thanks.
I will have to try getting both inputs to have the same 100% luminance and then check the green. Thanks.
DVI can apparently do both.
I have my HTPC connected to my plasma via a DVI port, using a DVI to HDMI cable, and can send either RGB or YCbCr.
I have my HTPC connected to my plasma via a DVI port, using a DVI to HDMI cable, and can send either RGB or YCbCr.
Smells like a 16-235 vs 0-255 thing to me. The difference is about what I'd expect if you sent a 235 white to a display calibrated for or expecting a 255 white.
Dave
Dave
I was curious if someone would bring that up. This is a known issue with the A2 and DVI connections, that the last firmware attempted to fix. Many still report problems and I was wondering if my measurements are telling me this is the problem. Or if it was just a brightness/contrast adjustment.
Quote:
Originally Posted by dlarsen /forum/post/12850737
Smells like a 16-235 vs 0-255 thing to me. The difference is about what I'd expect if you sent a 235 white to a display calibrated for or expecting a 255 white.
Dave
I was curious if someone would bring that up. This is a known issue with the A2 and DVI connections, that the last firmware attempted to fix. Many still report problems and I was wondering if my measurements are telling me this is the problem. Or if it was just a brightness/contrast adjustment.
OK, so I put up a 75% grayscale and measured Y over component. Then switched to DVI and upped contrast until the Y value was about the same. Then I compared green Y values using a 75% window. It is still way different over DVI.
pattern Component DVI DVI adjusted
75% gray x 0.314 0.314 0.314
75% gray y 0.334 0.330 0.335
75% gray Y 78.55 54.45 76.75
75% Grn x 0.287 0.287 0.287
75% Grn y 0.613 0.612 0.612
75% Grn Y 52.31 25.17 35.56
Thoughts?
pattern Component DVI DVI adjusted
75% gray x 0.314 0.314 0.314
75% gray y 0.334 0.330 0.335
75% gray Y 78.55 54.45 76.75
75% Grn x 0.287 0.287 0.287
75% Grn y 0.613 0.612 0.612
75% Grn Y 52.31 25.17 35.56
Thoughts?
1 - 14 of 14 Posts
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