RE: YCbCr
RE: YCbCr
- Subject: RE: YCbCr
- From: "Tim Vitale" <email@hidden>
- Date: Tue, 26 Jun 2007 16:27:57 -0700
- Importance: Normal
I have exactly the same issue.
I've noticed that in Charles Poynton's <Video Engineering> article listed in the Wikipedia
<YCbCr> article is down or missing (my browser had to be killed when it tried to open the
file for over 20 minutes). Fortunately, I had a copy of the PDF. I have attached an
image made from an image on one of pages (fair use, education purposes), but I don't
expect that it will make it through the list filters. Send me a message offline and I'll
send you the JPEG.
The image shows the YCbCr rectangle imposed over the R'G'B' cube. I'd guess it encloses
roughly 25% of the [relative] RGB space. [I have a copy taped to my screen.]
I guess what Marco is saying is, that that the "diagonal shoe-box shape of the YCbCr
space" with opposite corners touching the (1) max-black and (2) max-white points in the
centers of the faces of the R'G'B' cube, is "relative" to the gamut of the particular RGB
Color Space. It will be smaller in <sRGB> and larger in <ProPhoto RGB>.
I assume... that YCbCr space is relative to AdobeRGB 1998 or sRGB etc and can't be defined
without referencing a specific [device dependent] RGB space, within a particular, [device
independent] Lab (ColorThink) or XYZ/xyz, color space. I would also like to see such an
image in Chromix ColorThink. However, short of writing an YCC Color Space profile,
ourselves, relative to one of the standard RGB Color Spaces, we will not "find" such a
useful visual mnemonic.
Tim Vitale
Paper, Photographs &
Electronic Media Conservator
Film Migration to Digital Format
Digital Imaging & Facsimiles
Preservation & Imaging Consulting
Preservation Associates
1500 Park Avenue
Suite 132
Emeryville, CA 94608
510-594-8277
510-594-8799 fax
email@hidden <http://briefcase.yahoo.com/email@hidden>
[use of the above URL may require a "Yahoo! ID" to download files]
> -----Original Message-----
> From: colorsync-users-bounces+tjvitale=email@hidden
[mailto:colorsync-users-
> bounces+tjvitale=email@hidden] On Behalf Of Scott Ettin
> Sent: Tuesday, June 26, 2007 1:26 PM
> To: email@hidden
> Subject: YCbCr
>
> Marco,
>
> I run a digital media services department at Postworks in New York City.
> Clients give us their SD & HD tapes and we often get requests for image
> sequences, notably TIFF & TARGA files.
>
> We use an AJA Kona 3 card in our Quad G5s to 8 & 10-bit uncompressed
> Quicktimes and then export stills after capture.
>
> The reason that I wanted to see a YCbCr profile in Color Sync is because
> those still images exhibit dramatic chroma and luma clipping.
>
> When I use Maximum Throughput's Sledgehammer, there is no resampling of
> color and luminance.
>
> I'm trying to understand why. I have read this from Apple's Quicktime
> Developer page:
>
> http://developer.apple.com/quicktime/icefloe/dispatch027.html
>
> Scott
>
>
>
>
>
>
> Message: 3
> Date: Sat, 23 Jun 2007 12:44:04 -0700
> From: Marco Ugolini <email@hidden>
> Subject: Re: YCbCr Profile
> To: ColorSync Users Mailing List <email@hidden>
> Message-ID: <C2A2C614.F9CB%email@hidden>
> Content-Type: text/plain; charset="US-ASCII"
>
> In a message dated 6/22/07 12:54 PM, Scott A. Ettin wrote:
>
> > Hello list. I've just joined and have a question.
> >
> > I am looking for a YCbCr profile that I can load in ColorSync so that
> > I can view the color model and compare it to RGB.
> >
> > Can someone point me to an .ICC profile I can download?
>
>
> A note of warning regarding YCbCr:
>
> "YCbCr is not an absolute color space. It is a way of encoding RGB
> information, and the actual color displayed depends on the actual RGB
> colorants used to display the signal. Therefore a value expressed as
> YCbCr is only predictable if standard RGB colorants are used, or if an
> ICC profile is attached or implied which is used to translate value for
> the colorants in use."
> <http://en.wikipedia.org/wiki/YCbCr>
>
> Marco Ugolini
>
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Attachment:
Poynton_RGBto422_YUV_v1.gif
Description: GIF image
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