2006.09.16 09:58 "Re: [Tiff] is there alpha component present in Grayscale orPalettecolor image", by Anurag Singh

Thanks for reply..

i am using tiffcp.c for reading tiles n strips of images.

What I am thinking is an extra data plane, not an extra column in the

> color table

then how will i get extra data plane in palette images. I want all image data so please let me know how can i get it.

>Transparency and especially translucency are not always tied to the >color of a pixel (which would be the effect of the extra column in the >colortable), rather, it is often tied to position in the image (i.e. >vignettes around the edges)

>In that case, the advice for palette images would be the same as your >advice for the greyscale images.

So what should i understand?? i am getting that grayscale and palette both can have extra component. am i rt?

thanks

anurag

On 9/15/06, Bob Friesenhahn <bfriesen@simple.dallas.tx.us> wrote:

Gerben -

For palette images, is an alpha channel explicitly forbidden by the spec

?

What I am thinking is an extra data plane, not an extra column in the color table.

Right. An interesting issue is that libtiff requires that all samples be the same size so Pallete images using a small bits per sample for the index impose the same bits per sample restriction on the alpha channel. For an 8 bits per sample image, this is not usually a restriction, but it becomes more so for 2 or 4 bits per sample.

Associated alpha makes no sense since Pallete entries are not related to pixel position but associated alpha is related to pixel position.

> bfriesen@simple.dallas.tx.us,

http://www.simplesystems.org/users/bfriesen/

> GraphicsMagick Maintainer, http://www.GraphicsMagick.org/<http://www.graphicsmagick.org/>
>
>