Re: Transparency attribute in Bitmap class

Emmanuel BEUQUE (ebeuque@pratique.fr)
Tue, 3 Feb 1998 17:48:03 +0100

À (At) 13:25 +0200 3/02/98, Markku Savela écrivait (wrote) :
>> From: Emmanuel BEUQUE <ebeuque@pratique.fr>
>> I have found incredible that the dropOutColour attribute that was in DIS
>> has simply disappeared in IS. This feature is so widely used in the TV
>> world that this big loss always make authors angry.
>
>I can see some rationale for the disappearance of dropOutColor. It
>would work only for non-lossy image formats (such as GIF and PNG,
>which already have their own internal transparency).
>
>For JPEG and MPEG the exact color is problematic, because the decoded
>color value is only an approximation of the encoded color
>value. Putting a uniformly colored area into JPEG/MPEG, does not come
>out as single color value, the resulting transparency would be a
>random pixel here and there...

Correct. That's true that the ideal solution would have been to be able to
define a range of color components (either RGB or YUV or HSB) that should
be rendered as transparent (the same way as a video editing system).

But giving the GIF and PNG formats as a solution is pretty bad IMHO, since
they are possibly not the format used on STB. I think that the dropOutColor
was a better solution, and as far as JPEG and MPEG format are concerned,
the application domain could have defined a tolerance around the
dropOutColor value for pixels to be rendered transparent.

Of course, that's just my own opinion, but it is based on what I've heard
from the authors.
BR,
Emmanuel

__________________________________________________________________
Emmanuel BEUQUE mailto:ebeuque@pratique.fr
MediaServ tel: +33 (0) 2 99 64 35 64
Multimedia consultant & developer fax: +33 (0) 2 99 64 36 65