- fierodeval wrote, On 01.11.2008 21:59 Uhr:
> Yes, I understand. But when you speak about the "sqrt(2)", you are

Yes. correct. Because the cube faces *could* contain more information in

> speaking about the figure in the right of this image

> http://www.devalvr.com/fiero/equicube.jpg . Te correct figure is in

> the left and this figure is valid in the two directions.

>

> Then, if I understand correctly, you say that the figure for

> equirect->cube conversion is the left image and for cube->equirect is

> the right image?

the corners.

If the source was a equirectangular with 1/Pi as factor for the cube

faces size then it is safe to just use the left type of conversion again

because the pixels in corners are stretched by a factor of sqrt(2).

If the source images are cube faces, for example of a rendering from a

3D software, then you need to use the conversion on the right side to

avoid losing resolution/information.

The factor Pi*sqrt(2) would also be true if the equi->cube was executed

with a factor smaller then 1/Pi*sqrt(2) to get the maximum out of the

cube faces. Another case would be if you recover a equirectangular from

a QTVR where you don't know the original resolution.

--

MfG,

Thomas - Hi Thomas,

But, if the default value is width/4 you are using this figure:

http://www.devalvr.com/fiero/equicube2.jpg , loosing a lot of

information in the conversion.

If you take the output equirect from PTGui, all values superior to

3.14 in the divisor are loosing information in the conversion.

regards!

fiero

--- In PanoToolsNG@yahoogroups.com, Thomas Rauscher <yahoo@...> wrote:

>

> fierodeval wrote, On 01.11.2008 21:59 Uhr:

> > Yes, I understand. But when you speak about the "sqrt(2)", you are

> > speaking about the figure in the right of this image

> > http://www.devalvr.com/fiero/equicube.jpg . Te correct figure is in

> > the left and this figure is valid in the two directions.

> >

> > Then, if I understand correctly, you say that the figure for

> > equirect->cube conversion is the left image and for cube->equirect is

> > the right image?

>

> Yes. correct. Because the cube faces *could* contain more

information in

> the corners.

>

> If the source was a equirectangular with 1/Pi as factor for the cube

> faces size then it is safe to just use the left type of conversion

again

> because the pixels in corners are stretched by a factor of sqrt(2).

>

> If the source images are cube faces, for example of a rendering from a

> 3D software, then you need to use the conversion on the right side to

> avoid losing resolution/information.

>

> The factor Pi*sqrt(2) would also be true if the equi->cube was executed

> with a factor smaller then 1/Pi*sqrt(2) to get the maximum out of the

> cube faces. Another case would be if you recover a equirectangular

from

> a QTVR where you don't know the original resolution.

>

> --

> MfG,

> Thomas

>