2

I already made an image which I want to wrap around a sphere. However, I know if I were to try this, the top and bottom of the sphere would look like they are pinched.

I want to distort the image in a way so that it doesn't look pinched when wrapped around a sphere.

To clarify, I do NOT want to unwrap the sphere, I want to distort the image like the one below has been. I want to know how to do this to any image with no specific size or ratio.

distorted Mars texture

Edit for Billy: The image I posted above has the desired effect which I want, it is not the image that I want to be wrapped around a sphere.

Here is what I mean using the Earth instead of Mars.

Below is what I want the final product to look like. distorted Earth texture

Below is what my image would look like in comparison (this is not my image). "not" distorted Earth texture

See how the top of the first image looks stretched compared to the top image? That stretching is what I want it to have. That way, when the texture is placed on a sphere, the top and the bottom don't look pinched.

After writing all this, I found a great example. My image is like the top one in the picture below. I want it to look like the bottom one in the picture below.

texture map example

It doesn't look like it was done perfectly, but I hope it gets the idea across.

Thank you!

  • What application(s) are you using or would like to use? – GoofyMonkey Jul 6 '18 at 13:25
  • The computer I am working on has paint.net. I am not able to install any other programs in a short amount of time for the reason that it is a company computer, so paint.net would be preferred. I am open to any answer using any program, however. – user123410 Jul 6 '18 at 13:34
  • 1
    Thanks, that's a bit clearer. Unfortunately I have no idea. – Billy Kerr Jul 6 '18 at 14:33
  • Install blender. Project your image on the sphere and bake down – joojaa Jul 6 '18 at 15:10
  • I found this link and this link which seem to deal with the problem. – Billy Kerr Jul 6 '18 at 15:23
0

Commenting on an older post, I know:

What you're looking for are polar coordinates. In Photoshop that's in the Filter → Distort menu. A Paint.Net plugin that looks like it does it is here.

Billy mentioned this link, which explains it pretty well, even though it's old.

You'll need to know how to stitch an image together to make it tileable. (personally, I like to take a copy of the center of the image, feather the edges, and place it over both sides so that it repeats, then erase bits here and there to make it look seamless).

Then, use the filter to go rectangle to polar. You'll see the crazy pinch in the middle of your screen, fix it the same way you fixed your image to be tileable. Then use the opposite filter, Polar to Rectangle. After that, you'll see the distortion you're looking for on the top. To fix the bottom, rotate the image 180deg (or flip it) and do it again.

And then you're done!

0

You will probably need to start over. The image will need to have, essentially, a different scale factor for every pixel row, and the scale factor increases parabolically as you move from the equator.

It is a non-trivial subject and you will need to read up on Mercator projection if you want to approximate it by hand.

The Wikipedia entry has some good visual aids that highlight how scale factor increases by distance.

So in your sample image, the top portion looks like the image below when applied to a sphere. Assuming the top pixel row of your image is the point through which the axis passes, then the entire first pixel row of your image is rendered to 1 px.

You will need to account for this in your manual render.

As a possible algorithm to fake it with an existing image, starting from the center:

  • take one row above (1st time, just center);
  • copy and place in new image at same location;
  • stretch this row to fit (1st time, no stretch);
  • take one row below (1st time, just center);
  • copy and place in new image at same location;
  • stretch this row to fit (1st time, no stretch);
  • reduce width by the proper ratio;
  • repeat

Laborious, but it may help you visualize how the scale works in the image you provided.

enter image description here

  • look especially at the scale factor section in the wiki entry. – Yorik Jul 6 '18 at 14:32
0

My two cents.

This is not a trivial task. In my opinion, the distortion cannot be generated properly by hand.

It is a projection distortion. And there are different kinds of distortions to be projected on a sphere.

Mainly, a cylindrical, spherical and cubical.

I would use a panorama stitcher like Hugin http://hugin.sourceforge.net/ to stitch different patterns.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy