Hello! I created a picture with a gradient. I want to use it as a height map for
a sphere. However, only gray stripes are visible on the sphere.

#version 3.7;
#include "shapes.inc"

global_settings {
    assumed_gamma 1.000000
    max_trace_level 3
    charset utf8
}
sky_sphere {
    pigment {rgb<0.051, 0.051, 0.051>}
}

#declare Default_texture = texture{pigment {rgb 0.8}}

#declare Material = texture{
    pigment{color srgbft <0.8000,0.8000,0.8000,0.0000,0.0000>}
    finish{
        diffuse 0.8000
        brilliance 1.8000
          }
}
#declare Material_001 = texture{
    pigment{color srgbft <0.8000,0.8000,0.8000,0.0000,0.0000>}
    normal{ bump_map{"/home/lanuhum/src/Thread_90.jpg" gamma 1.1000 map_type 0
interpolate 2 bump_size 5}
        translate <0.0000,0.0000,0.0000>
        rotate <0.0000,0.0000,0.0000>
        scale <1.0000,1.0000,1.0000>/1
        }
    finish{
        diffuse 0.8000
        brilliance 1.8000
          }
}
#declare data_Sphere_shape_ob = sphere { 0,1
    texture {Material_001}
    matrix <1.000000, 0.000000, 0.000000,  0.000000, 1.000000, 0.000000,
0.000000, 0.000000, 1.000000,  0.000000, 0.000000, 0.000000>
}
#include "data_Cube_dec.inc"

object {data_Sphere_shape_ob
    matrix <1.000000, 0.000000, 0.000000,  0.000000, -0.000000, -1.000000,
0.000000, 1.000000, -0.000000,  0.000000, 0.000000, 0.000000>
}
object {data_Cube_ob
    matrix <1.000000, 0.000000, 0.000000,  0.000000, -0.000000, -1.000000,
0.000000, 1.000000, -0.000000,  0.000000, 0.000000, 0.000000>
}
light_source {
    <4.08,5.9,-1.01>
    color rgb<1, 1, 1>
    fade_distance 29.9999828339
    fade_power 1
}
camera {
    perspective
    location  <0,0,0>
    look_at  <0,0,-1>
    right <-1.7777777777777777, 0, 0>
    up <0, 1, 0>
    angle  49.134343
    rotate  <-26.440706, 46.691945, -0.000003>
    translate <7.481132, 5.343666, 6.507640>
}

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Attachments:
Download 'bump_map.jpg' (64 KB)

Preview of image 'bump_map.jpg'

"LanuHum" <Lan### [at] yandexru> wrote:
> Hello! I created a picture with a gradient. I want to use it as a height map for
> a sphere. However, only gray stripes are visible on the sphere.

That's because you're only perturbing the normal vectors on the smooth sphere to
make the light reflect in different directions than it normally would, and so
produce the illusion that there is a "texture" on the surface when there isn't.

There are articles on the web and maybe a POV-Ray FAQ that show the shadows cast
by objects that are really shaped that way vs a smooth object with a normal map.

What you want to do is "surface displacement" where you actually change the
geometry of the surface of your sphere.

Luckily, myself, WFP, and Maetes have worked on this.

Your best bet is to use whatever function makes your stripes to modulate the
radius of your sphere so that those points have the actual height dictated by
the function.

https://news.povray.org/povray.binaries.images/thread/%3C5f16dc29%40news.povray.org%3E/

https://news.povray.org/povray.advanced-users/thread/%3Cweb.67b47b18cb1bd5e34d0a98d30225ff5%40news.povray.org%3E/

You can also look at Mike Williams' isosurface tutorial where he has several
examples of using functions to change the surface of a sphere.

Hope that helps.

- BE

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"Bald Eagle" <cre### [at] netscapenet> wrote:
> "LanuHum" <Lan### [at] yandexru> wrote:
> > Hello! I created a picture with a gradient. I want to use it as a height map for
> > a sphere. However, only gray stripes are visible on the sphere.
>
> That's because you're only perturbing the normal vectors on the smooth sphere to
> make the light reflect in different directions than it normally would, and so
> produce the illusion that there is a "texture" on the surface when there isn't.
>
> There are articles on the web and maybe a POV-Ray FAQ that show the shadows cast
> by objects that are really shaped that way vs a smooth object with a normal map.
>
> What you want to do is "surface displacement" where you actually change the
> geometry of the surface of your sphere.
>
> Luckily, myself, WFP, and Maetes have worked on this.
>
> Your best bet is to use whatever function makes your stripes to modulate the
> radius of your sphere so that those points have the actual height dictated by
> the function.
>
>
https://news.povray.org/povray.binaries.images/thread/%3C5f16dc29%40news.povray.org%3E/
>
>
https://news.povray.org/povray.advanced-users/thread/%3Cweb.67b47b18cb1bd5e34d0a98d30225ff5%40news.povray.org%3E/
>
> You can also look at Mike Williams' isosurface tutorial where he has several
> examples of using functions to change the surface of a sphere.
>
> Hope that helps.
>
> - BE

I understand. Thank you.

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"LanuHum" <Lan### [at] yandexru> wrote:
> Hello! I created a picture with a gradient. I want to use it as a
> height map for a sphere. However, only gray stripes are visible on the sphere.
>

The 'flat' look of those gray stripes seems odd to me; there *should* be some
(fake) 'depth' to them due to your bump_map, based on the normal-pattern image
that you posted:

normal{ bump_map{"/home/lanuhum/src/Thread_90.jpg"
gamma 1.1000 map_type 0
interpolate 2 bump_size 5}

I ran your code--using the same 'normal' image that I copied here-- and it seems
that a gamma of 1.1 that you used is not a good value for a bump_map. I changed
that value to 2.2 (and boosted the bump_size to 10) and it looks much better.

If I leave out the gamma keyword altogether, the 'flat' result looks nearly
identical to your 1.1 value. The POV-ray default is 1.0 (i.e., it treats the
image as 'linear' data.)

Since we are both using jpeg's for the bump_map, they have a standard 'embedded
gamma' of around 2.2 (or maybe 'srgb'), which is not linear. So using a value of
1.1 (or 1.0) changes that; a somewhat simple explanation is that it reduces the
contrast of the image-as-bump_map.

From the documentation:
"While POV-Ray will normally interpret the bump map input file as a container of
linear data [gamma of 1.0] irregardless of file type, this can be overridden for
any individual bump map input file by specifying gamma immediately after the
file name."

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Attachments:
Download 'bump_map_gamma_comparison_kw.jpg' (41 KB)

Preview of image 'bump_map_gamma_comparison_kw.jpg'

"Kenneth" <kdw### [at] gmailcom> wrote:
> "LanuHum" <Lan### [at] yandexru> wrote:
> > Hello! I created a picture with a gradient. I want to use it as a
> > height map for a sphere. However, only gray stripes are visible on the sphere.


> I ran your code--using the same 'normal' image that I copied here-- and it seems
> that a gamma of 1.1 that you used is not a good value for a bump_map. I changed
> that value to 2.2 (and boosted the bump_size to 10) and it looks much better.


Good work digging a little deeper into this.
I was just checking in during morning coffee, and then heading straight out.

Depending on what the final use case is, he might want consistent/believable
shadows to go along with that deep scalloped surface.
Also, it seems a little silly to evaluate the function to make an image that
then gets used as a bump map - when he can just plug it straight into an
isosurface and get better results without all of the extra workflow and
processing.

However your experiments are not without value.  I think it would be a nice
demonstration scene if you made a grid of spheres each with different gamma
handling and bump sizes - AND had them all cast shadows onto a plane.

If you share your thoughts about how the image gets converted to gamma 2.2 or
srgb-modified rgb values, and I can pipe that into the isosurface equations for
a parallel rendering and comparison.

- BE

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On 16.03.2026 14:20, Kenneth wrote:
> The 'flat' look of those gray stripes seems odd to me; there *should* be some
> (fake) 'depth' to them due to your bump_map,

Absolutely agree. But I was unable to find the reason why the result do 
not conform with my expectations.

> I changed
> that value to 2.2

Aha! That that seem be that evasive reason!

Thank you, that sort of explains things.

-- 
Ilyich the Toad
https://dnyarri.github.io/

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"Kenneth" <kdw### [at] gmailcom> wrote:
> "LanuHum" <Lan### [at] yandexru> wrote:
> > Hello! I created a picture with a gradient. I want to use it as a
> > height map for a sphere. However, only gray stripes are visible on the sphere.
> >
>
> The 'flat' look of those gray stripes seems odd to me; there *should* be some
> (fake) 'depth' to them due to your bump_map, based on the normal-pattern image
> that you posted:
>
> normal{ bump_map{"/home/lanuhum/src/Thread_90.jpg"
> gamma 1.1000 map_type 0
> interpolate 2 bump_size 5}
>
> I ran your code--using the same 'normal' image that I copied here-- and it seems
> that a gamma of 1.1 that you used is not a good value for a bump_map. I changed
> that value to 2.2 (and boosted the bump_size to 10) and it looks much better.
>
> If I leave out the gamma keyword altogether, the 'flat' result looks nearly
> identical to your 1.1 value. The POV-ray default is 1.0 (i.e., it treats the
> image as 'linear' data.)
>
> Since we are both using jpeg's for the bump_map, they have a standard 'embedded
> gamma' of around 2.2 (or maybe 'srgb'), which is not linear. So using a value of
> 1.1 (or 1.0) changes that; a somewhat simple explanation is that it reduces the
> contrast of the image-as-bump_map.
>
> From the documentation:
> "While POV-Ray will normally interpret the bump map input file as a container of
> linear data [gamma of 1.0] irregardless of file type, this can be overridden for
> any individual bump map input file by specifying gamma immediately after the
> file name."

My sincere apologies. I missed your message. Thank you so much for your help

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Attachments:
Download 'screenshot.jpg' (104 KB)

Preview of image 'screenshot.jpg'

"Bald Eagle" <cre### [at] netscapenet> wrote:
> "Kenneth" <kdw### [at] gmailcom> wrote:
> >
> > I ran your code--using the same 'normal' image that I copied here-- and it
> > seems that a gamma of 1.1 that you used is not a good value for a bump_map.
> > I changed that value to 2.2 (and boosted the bump_size to 10) and it
> > looks much better.
>
>
> If you share your thoughts about how the image gets converted to gamma 2.2 or
> srgb-modified rgb values...

[Sorry for the long delay in responding here; I had to deal with repairs on my
car, one after the other.]

I have been trying to reproduce Lanahum's flat-looking result with my *own*
image(s) for the bump_map, made in POV-ray at typical assumed_gamma 1.0-- and
see 'normals' results  that sometimes do not agree with my previous comments
about the  bump_map's gamma setting requiring a 2.2 value. (I'm running the
tests in v3.7, same as he did.) The surface normals in at least one of my tests
look OK even with the bump_map's gamma at 1.0 (or just leaving out 'gamma'
altogether). That seems strange, based on my earlier remarks. But I finally
'chased the rabbit down its hole' and discovered the reason for the disparity.

Simply put: The final appearance of the 'normal' effect is very sensitive to the
gamma used to encode its image_map (and sensitive to the chosen pattern itself,
apparently.)

NOTE: In the attached image, all of the bump_maps use bump_size 10 for the
normal.

[A] While the default 'gamma' setting in a bump_map does indeed seem to be 1.0,
my new tests indicate that POV-ray automatically compensates for an image having
an intrinsic or 'encoded' gamma of 2.2-- like typical  jpeg's or png's-- and
*without* having to specify a gamma-value change in the bump_map. (I used an
inverted sine_wave pattern for this one; I took the original sine_wave .jpeg
render into my paint.net app and inverted it there.) It's 'normals' look as
expected!

[B] This is just Lanahum's posted pattern again and his original bump_map
result, then with my gamma 2.2 'correction' as before. (To use his pattern, I
simply snipped it out of his .jpeg image post-- using paint.net--and re-saved it
as a .jpeg again.) The final 'normals' result looks like a 'scallop wave'-- but
that's misleading...

[C] To create a pattern that looks like his, I had to use a triangle_wave
pattern instead-- with the image_map **rendered  at assumed_gamma 2.2** in
POV-ray, rather than at my usual 1.0.  It looks nearly identical to Lanahum's
pattern. Using that image in the bump_map-- with a gamma 1.0 setting there--
produces the flat gray-stripes look again, same as Lanahum's.  A setting of 2.2
gives the surface normals some 'depth'...although the result looks like a
'scallop wave' instead of a triangle. That's to be expected: The gamma is
changing the 'slope' of the black-to-white gradations.

[There is another way to produce the same effect, which I didn't post here:
making a triangle-wave image_map *as* a gamma 1.0 image. I made one in POV-ray
using assumed_gamma 1.0 and changing both Display_Gamma and File_Gamma to 1.0,
rather than their usual 2.2 (or 'srgb'). Then it likewise required a gamma 2.2
value in the bump_map. BTW, this image_map had to be in the .png format--
apparently a .jpeg cannot(?) be rendered at gamma 1.]

I think that Lanahum's original image_map was made using one those two schemes--
which is why it required a 2.2 gamma change.

[D] I used POV-ray's triangle_wave pattern again for the image_map, but rendered
at typical assumed_gamma 1.0. With the bump_map's gamma set to 1.0, there
appears to be *some* 'depth' to the normal-- but changing the gamma to 2.2 makes
flat stripes instead(!), which is a mystery. To get any further depth from it
requires a bump_map gamma of between 4 and 5 (4.4??)-- but then it looks like a
'scallop wave' again.

--------------------
[off topic]
Lanahum's code uses a 'brilliance' setting in his finish{...}. That seems to
work (or look) better in v3.7 than in v3.8 beta 1, to my eyes. There must have
been a 'change' of some kind for the current betas.

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Attachments:
Download 'bump_map_tests_3_23_2026_kw.jpg' (561 KB)

Preview of image 'bump_map_tests_3_23_2026_kw.jpg'

Nice work producing all those variants.

I'm curious:

In some of your renders you get a mis-match / seam in your normal/texture.
Also, there is that small half-black/half-white circular "blemish" at the
forefront of some of the spheres.

- BE

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"Bald Eagle" <cre### [at] netscapenet> wrote:
>
> In some of your renders you get a mis-match / seam in your normal/texture.
> Also, there is that small half-black/half-white circular "blemish" at the
> forefront of some of the spheres.
>

The mis-match seam comes from my attempt to give my own image_map the same
'tilt' of the pattern as Lanahum's...although I didn't get it quite right. Then
the pattern repeats on the sphere, causing the visible 'seam'.

That small circle on my sphere renders is also visible in Lanahum's original
post, although not as pronounced. I don't quite know what the cause is, as I
have not really examined his code in detail, and just used it as-is. (Although,
I did comment-out his various matrices to simplify the code, since they were
having no effect as far as I could tell.) The circle might be because the
bump_map's image_map does not exactly fit the sphere(?) or is not exactly
aligned to it. (We are both using map_type 0 for applying the bump_map, which is
just planar mapping, not 'spherical')

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