Computer Graphics with Photoshop - Extracting an anti-aliased curve from a white background?

Author

Extracting an anti-aliased curve from a white background?

Chris

2003-11-27, 5:42 pm

Hello,
I have a scanned gray scale signature, because of the scan it's
effectively anti-aliased already. However, it's anti-aliased to the
white background it was written on. Is there someway to tell photoshop
to convert the different shades of gray to black with a corresponding
transparency value (i.e. so that it would be effectively anti-aliased
over a transparent background rather than white) as I want to paste it
over the top of an image.

I think it would be a pretty simple operation to perform
(theoretically) and the only information needed should be that solid
color is black anti-aliased to white background so calculate the
transparency value to give a particular gray over the white. But
whether there is some easy option to do it I'm not sure!

I have tried the Image -> Extract... option. This doesn't seem to do a
perfect job as I tested it by drawing a 'perfectly' anti-aliased curve
with a paint brush tool onto a white background and then tried to
extract it back out off the white, it was ok but far from perfect
compared to the original. It seems a lot of fiddling around as well.

Any ideas or suggestions welcome! I need to buy a book on photoshop!

Using photoshop 6.0.1 by the way.

Thanks for any help/suggestions

Stuart

2003-11-27, 5:42 pm

You could use the contrast and brightness to make the black darker and
the white brighter then use magic wand to select and remove the white
areas. See what that does for you. I'm no expert but that seems to be a
simple way to achieve the result, I sure others will have different ways
of doing it.

Stuart

Chris wrote:

quote:

> Hello,
> I have a scanned gray scale signature, because of the scan it's
> effectively anti-aliased already. However, it's anti-aliased to the
> white background it was written on. Is there someway to tell photoshop
> to convert the different shades of gray to black with a corresponding
> transparency value (i.e. so that it would be effectively anti-aliased
> over a transparent background rather than white) as I want to paste it
> over the top of an image.
>
> I think it would be a pretty simple operation to perform
> (theoretically) and the only information needed should be that solid
> color is black anti-aliased to white background so calculate the
> transparency value to give a particular gray over the white. But
> whether there is some easy option to do it I'm not sure!
>
> I have tried the Image -> Extract... option. This doesn't seem to do a
> perfect job as I tested it by drawing a 'perfectly' anti-aliased curve
> with a paint brush tool onto a white background and then tried to
> extract it back out off the white, it was ok but far from perfect
> compared to the original. It seems a lot of fiddling around as well.
>
> Any ideas or suggestions welcome! I need to buy a book on photoshop!
>
> Using photoshop 6.0.1 by the way.
>
> Thanks for any help/suggestions
>

Sami

2003-11-27, 5:42 pm

Hi,

Easiest way I've found is to use Mark McLaren's handy Remove White -filter
which does exactly what you describe. Filter can be found from here:
http://pluginspt.pluginshost.com/FreePlug/mark.html

Sami

On 27 Nov 2003 00:50:06 -0800, Chris <chris554466@hotmail.com> wrote:

quote:

> Hello,
> I have a scanned gray scale signature, because of the scan it's
> effectively anti-aliased already. However, it's anti-aliased to the
> white background it was written on. Is there someway to tell photoshop
> to convert the different shades of gray to black with a corresponding
> transparency value (i.e. so that it would be effectively anti-aliased
> over a transparent background rather than white) as I want to paste it
> over the top of an image.
>
> I think it would be a pretty simple operation to perform
> (theoretically) and the only information needed should be that solid
> color is black anti-aliased to white background so calculate the
> transparency value to give a particular gray over the white. But
> whether there is some easy option to do it I'm not sure!
>
> I have tried the Image -> Extract... option. This doesn't seem to do a
> perfect job as I tested it by drawing a 'perfectly' anti-aliased curve
> with a paint brush tool onto a white background and then tried to
> extract it back out off the white, it was ok but far from perfect
> compared to the original. It seems a lot of fiddling around as well.
>
> Any ideas or suggestions welcome! I need to buy a book on photoshop!
>
> Using photoshop 6.0.1 by the way.
>
> Thanks for any help/suggestions

--
Using M2, Opera's revolutionary e-mail client: http://www.opera.com/m2/

Ilya Razmanov

2003-11-27, 5:42 pm

"Chris" <chris554466@hotmail.com> wrote in message
news:48059e8e.0311270050.3ccae9fe@posting.google.com...

quote:

> Hello,
> I have a scanned gray scale signature, because of the scan it's
> effectively anti-aliased already. However, it's anti-aliased to the
> white background it was written on. Is there someway to tell photoshop
> to convert the different shades of gray to black with a corresponding
> transparency value (i.e. so that it would be effectively anti-aliased
> over a transparent background rather than white) as I want to paste it
> over the top of an image.

There are much too many ways to do that. If the background is *really*
white, you may simply set the merge mode for that layer to "Multiply" and
place it over anything. Or you may load this greyscale channel as
transparency. Or you may download my own plugins from
http://photoshop.msk.ru/ (the one you are looking for is located at
http://www.illustrator.ru/catalog/s...parency_e.shtml
specifically but you may also take a look to the others) and use it to
directly convert luminocity into transparency.

Ilyich.
--------------------------------------------------------------------------
Ilya Razmanov (a.k.a. Ilyich the Toad)
http://photoshop.msk.ru/ - Photoshop plug-in filters
"Umgah are funny. We are Umgah. We are funny. There's no alternative" -
Umgah,
Star Control 2: The Ur-Quan Masters
--------------------------------------------------------------------------

Peter Wollenberg

2003-11-27, 5:42 pm

chris554466@hotmail.com (Chris) wrote:

quote:

>Hello,
>I have a scanned gray scale signature, because of the scan it's
>effectively anti-aliased already. However, it's anti-aliased to the
>white background it was written on. Is there someway to tell photoshop
>to convert the different shades of gray to black with a corresponding
>transparency value (i.e. so that it would be effectively anti-aliased
>over a transparent background rather than white) as I want to paste it
>over the top of an image.
>

Try the following:

1. duplicate the background layer of the target image
2. put the text as is on top
3. set the blending mode of the text layer to "darken"
4. merge down
5. set the blending mode of the merged layer to "luminosity"
6. merge down
HTH, Peter

Chris

2003-11-27, 5:42 pm

Great! Thank you, I'll download it and see what it does :-)

Hmm with first suggestion, adjusting brightness and contrast would
allow the magic wand to completely select the anti-aliased area (you
can probably adjust the wand settings to do this without adjust
brightness/contrast..?) but I think you'll still have the problem that
the pixels in that region will remain gray pixels and not
semi-transparent black pixels? Unless I misinterpreted what you meant?

Thanks for the posts :-)