### Re: Bumpmap with negative Depth ??

```
lasm [EMAIL PROTECTED] writes:

Thanks for your explanation. I am not familiar with the
algorithm.. but just curious, would there be any difference
if the Depth takes in negative integer (currently only positive
accepted) ? Can you comment on this ?

It wouldn't make any difference.  The surface normal vectors would
just point in the other direction, which is what you already get with
"invert bumpmap".

Federico

```

### Re: Bumpmap with negative Depth ??

```
"Steinar H. Gunderson" [EMAIL PROTECTED] writes:

The question is: Does it use 255-bm or just -bm? And would that make any
difference?

It wouldn't change anything.  The local differences that are used to
compute the surface normal would be exactly the same.

Dude, follow the math!  Read the source!

Federico

```

### Re: Bumpmap with negative Depth ??

```
lasm [EMAIL PROTECTED] writes:

Thanks for your explanation. I am not familiar with the
algorithm.. but just curious, would there be any difference
if the Depth takes in negative integer (currently only positive
accepted) ? Can you comment on this ?

NO. the bm plugin takes the intensity of the bm. "invert bumpmap" just
inverts the bm aka: the depth values are used as if they were
negative.

```

### Re: Bumpmap with negative Depth ??

```
On Tue, Jan 30, 2001 at 12:53:59PM +0100, Jens Lautenbacher wrote:
Thanks for your explanation. I am not familiar with the
algorithm.. but just curious, would there be any difference
if the Depth takes in negative integer (currently only positive
accepted) ? Can you comment on this ?
NO. the bm plugin takes the intensity of the bm. "invert bumpmap" just
inverts the bm aka: the depth values are used as if they were
negative.

The question is: Does it use 255-bm or just -bm? And would that make any
difference?

/* Steinar */
--
Homepage: http://members.xoom.com/sneeze/

```

### Re: Bumpmap with negative Depth ??

```
On 28 Jan 2001 17:20:39 +0100, Rebecca J. Walter wrote:
what if you color invert the one you use as the bump map?
if you use same layer, then duplicate, color invert, and use the
inverted to bump the regular.

Sorry?
I still don't see what this is about. the bumpmap layer used internally
in the case of a non graya layer is still only the grayscale value of
the layer.  color inverting the bm-layer and using this result as the bm
may produce something, but why should this be more correct than using
the "invert" button in the bm plugin?

but maybe I just don't understand what you want to do correctly.

jtl

```

### Re: Bumpmap with negative Depth ??

```
What he is suggesting is to invert the color value, so white
becomes black, and black areas become white, so that the bumpmap
will take a different height field to achieve the "inverse" effect..
I have tried it before but do not quite like the result..

IMHO, the PS Lighting effects did it more "politically correct".
If you press the "inverse bumpmap" there, the effect is different
from the "Invert" Bump Map in Gimp.. Just try it out yourself and
see if you agree... don't ask me to explain, I can't .. ;-)

re,
lasm
gallery -
http://gug.sunsite.dk/gallery.php?artist=41

--- In [EMAIL PROTECTED], Jens Lautenbacher [EMAIL PROTECTED] wrote:
On 28 Jan 2001 17:20:39 +0100, Rebecca J. Walter wrote:
what if you color invert the one you use as the bump map?
if you use same layer, then duplicate, color invert, and use the
inverted to bump the regular.

Sorry?
I still don't see what this is about. the bumpmap layer used
internally
in the case of a non graya layer is still only the grayscale value
of
the layer.  color inverting the bm-layer and using this result as
the bm
may produce something, but why should this be more correct than
using
the "invert" button in the bm plugin?

but maybe I just don't understand what you want to do correctly.

jtl

```

### Re: Bumpmap with negative Depth ??

```
[EMAIL PROTECTED] writes:

What he is suggesting is to invert the color value, so white
becomes black, and black areas become white, so that the bumpmap
will take a different height field to achieve the "inverse" effect..
I have tried it before but do not quite like the result..

IMHO, the PS Lighting effects did it more "politically correct".
If you press the "inverse bumpmap" there, the effect is different
from the "Invert" Bump Map in Gimp.. Just try it out yourself and
see if you agree... don't ask me to explain, I can't .. ;-)

The Bumpmap plug-in works by taking the intensity values to be height
values and computing the surface normal at each point.  Then it does
simple Gouraud-like shading on the destination image.  Inverting the
bumpmap source is exactly the same as using the "invert" button on the
plug-in's dialog box; the intensity values are inverted and the
surface normals will point in the opposite direction.

I.e. it is essentially a cheap embossing effect.

Photoshop's Lighting Effects produces much better results because it
actually does Phong shading of the image, and it general it has better
lighting models that you can choose.  You can do this in the GIMP with
Tom Bech's plug-in of the same name.

Federico

```

### Re: Bumpmap with negative Depth ??

```
Thanks for your explanation. I am not familiar with the
algorithm.. but just curious, would there be any difference
if the Depth takes in negative integer (currently only positive
accepted) ? Can you comment on this ?

If the bumpmap can be improved, many other scripts/plugins
which calls this will benefit from it..

re,
lasm

gallery-
http://gug.sunsite.dk/gallery.php?artist=41

--- Federico Mena Quintero [EMAIL PROTECTED] wrote:

The Bumpmap plug-in works by taking the intensity values to be height
values and computing the surface normal at each point.  Then it does
simple Gouraud-like shading on the destination image.  Inverting the
bumpmap source is exactly the same as using the "invert" button on
the
plug-in's dialog box; the intensity values are inverted and the
surface normals will point in the opposite direction.

I.e. it is essentially a cheap embossing effect.

Photoshop's Lighting Effects produces much better results because it
actually does Phong shading of the image, and it general it has
better
lighting models that you can choose.  You can do this in the GIMP
with
Tom Bech's plug-in of the same name.

Federico

=

Master's New Millennium Lecture Tour in Asia 2000 !!!
see http://www.godsimmediatecontact.com

visit these great web sites at
http://www.GodsImmediateContact.com/INTRODUCTION_video.html
http://members.xoom.com/meditations/

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```

### Re: Bumpmap with negative Depth ??

```
[EMAIL PROTECTED] writes:

Nope, that is not it.. Unfortunately, the Invert Bumpmap
option works just like the Azimuth, it changes the direction
of light 180 degrees, e.g. from NE to SW. That doesn't
do much to create the "carved in" effect.

??? what is carved in supposed to mean, then? the impression of height
in bumpmap is only achieved by the gradient ("the direction of light").

In fact it is a bit redundant as you can always tweak the Azimuth
value to achieve the "Invert Bumpmap" thing, unless of course, there
is a bug in the way "Invert Bumpmap" is supposed to works...

invert bumpmap means what it says: invert the mode of operation.

otherwise in theory at least, a negative depth value will
creat a sinking crater instead of a raised emboss... ??

yes. but that's what invert means. change the gradient so one has the
impression of a sunken (or raised, depending on the bumpmap) "crater".

This kind of thing is being done probably dozens of time
for any single project and it should be made simple and
easy to do... In PS there is a layers effect which can
apply emboss/carve in a jiffy. Short of that one will have
to create endless repetitive highlights and shadows just
to carve in, and I am a bit too lazy to do that..;-)

a layer mode is nice of course, but invert still does the right
thing. no need for experiments.

jtl

```

### Re: Bumpmap with negative Depth ??

```
lasm wrote:

Hi All,

snipped...I was trying to look for an engraved effect, the opposite
of emboss, i.e. to make the thing look caved in, instead of
popped out.

Short answer: "Invert bumpmap"

Long answer: Beware the sneaky qualities of human perception.

Make a grey "altitude map" of a cone (white means "high", black means "low")

0. Grey field. R = G= B= 127.
1. Foreground color white, background color black
2. Blend tool. Options: Mode - Lighten Only. Gradient - Radial
All other options default
3. Make a fuzzy white circle - the altitude map of a cone.
4. Filters-Map-BumpMap. Assuming default settings.
Manipulate the preview until you find your cone.

Now, one person perceives "light" streaming in from the northwest,
highlighting a raised conical hill. But, not knowing the settings,
another person perceives "light" streaming in from the southeast,
lighting the northwest rim of a conical depression. Same bitmap.
Different perceptions. You can flip the perceptions in your own
head with a little practice, so one person's emboss is another
person's intaglio. This arises from the simple, straightforward
interpretation of the first derivative of the altitude map as a kind
of "light". Unlike real light, there is an absence of other cues
to give a sense of "real" height or depth.

Given this phenomenon of dual perception, it is hard to "improve"
the bump map plugin with "absolute" embossing or intaglio properties.

Be good, be well

Garry

```

### Re: Bumpmap with negative Depth ??

```
On Thu, Jan 25, 2001 at 10:10:40PM -0800, lasm wrote:
Hi All,

I have been using the bumpmap plugin quite a lot lately.
It produces some very good embossy effects and I am very happy with the
results, thanks to the effort of the programmer.

I was trying to look for an engraved effect, the opposite
of emboss, i.e. to make the thing look caved in, instead of
popped out. While I couldn't find any plugin that does this,
I thought of an idea, if the bumpmap can be changed to accept
negative depth, in addition to positive integers, would it then
achieve the "engraved" effect ?

I think the "reverse" option is what you are looking for.  Also play around
with azmuth.

- Tal

--
-- --
|   Tal Danzig |  Libranet Linux  |
| [EMAIL PROTECTED] | The TOP Desktop! |
| http://tal.thepenismightier.net/ | http://www.libranet.com/ |
-- --

Beneath the rule of men entirely great, the pen is mightier than the sword.
-- Edward G Bulwer

```

### Re: Bumpmap with negative Depth ??

```
lasm wrote:
I was trying to look for an engraved effect, the opposite
of emboss, i.e. to make the thing look caved in, instead of
popped out. While I couldn't find any plugin that does this,
I thought of an idea, if the bumpmap can be changed to accept
negative depth, in addition to positive integers, would it then
achieve the "engraved" effect ?

I think the effect you are talking about is called 'Carve-It'.

Cheers!

Kevin.  (http://www.interlog.com/~kcozens/)

Internet:kcozens at interlog.com   |"What are we going to do today, Borg?"
or:ve3syb at rac.ca  |"Same thing we always do, Pinkutus:
Packet:ve3syb@va3bbs.#scon.on.ca.na|  Try to assimilate the world!"
#include disclaimer/favourite|  -Pinkutus  the Borg

```