[Tig] Barco 'Extended Gamma'

Stojmenovik, Goran goran.stojmenovik at barco.com
Tue Nov 9 12:05:57 GMT 2010


Hi Cem

What firmware are you using? You can check it by pressing the 'info'
button located on the left, between the 'power' button and 'CAL' button.

The RHDM allows setting both the gamma value (exponent) and the shape of
the gamma curve (OETF).

As the gamma is an electronic look up table, it is applied per input
window and so you can access the gamma menu behind the input selection
buttons '1' and '2' on the control box (press the button for 2-3
seconds).
The standard gamma value is 2.35.

To state an important thing upfront, Rec.709 or xvYCC are not
recommended shapes for the gamma curve for normal use. They will
perfectly invert the Rec.709-encoded video, but this is not the
intention, as this is not what was done on the CRT. This will introduce
a steep linear part in the shadows, and as a result the blacks will be
very bright. This can be used only for testing purposes.

The two other gamma-shape options you can use are Pure gamma and
Extended gamma. Pure gamma transmits all 'legal' video levels towards
the monitor using a normal power curve with the specified exponent. The
Extended gamma is identical to pure gamma in the legal video range, but
it allows out of gamut levels to be shown on the RHDM, (they can be
shown because of the wide-gamut LED backlight). The CRT did a similar
thing, because it could 'overdrive' the primaries. For most if not all
practical purposes (video-related), the two gamma shapes will give
identical results.

Compare the Rec.709 video encoding with the 'xvYcc' encoding. The
difference is that xvYcc extends the gamma curve to signal levels
outside the legal range in order to allow transmission of wide gamut
colors.

I will send you a 'tutorial' presentation explaining this in more
detail.

Whoever else wants more info on RHDM, feel free to contact me.

Goran Stojmenovik
Product Manager Displays
Barco


-----Original Message-----
From: Cem Ozkilicci [mailto:cemoz101 at yahoo.com] 
Sent: vrijdag 5 november 2010 14:57
To: Telecine Internet Group
Subject: [Tig] Barco 'Extended Gamma'

Hi Everyone,

I'm currently using the Barco RHDM-2301 and noticed that my monitor is
hard-set 
to an 'extended gamma' setting. I've been told that the monitor had to
be 
shipped to Barco to get this feature upgrade and is not something that
could be 
done on-site. Supposedly the reason why Barco has developed this is to 
'simulate' a CRT monitor. What I'd like to know is what does this
actually 
entail? 


I find it odd that if the change is in fact ONLY a gamma adjustment, why
can't 
we simply change it in the menus of the 2301 because there is an option
where 
you can play around with the gamma setting (2.35... bla bla bla).

Cheers!

Cem Ozkilicci
Colourist
Storyline Studios / Oslo





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