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HDRI Discussion Help Thread

RexRedRexRed Posts: 1,374
edited March 2020 in Technical Help (nuts n bolts)

This thread is created so people can get HDRI questions answered.

And wow, do I have some questions!

For instance, 

How exactly is HDRI a "projection"? Is it projected from the infinite dome into the scene or from the center of the scene to the infintie dome and then light/color bouncing off the infinite dome back into the scene?

Is the HDRI map simply laid/stretched upon/around an "infinite/finite dome" or is it something that is projected onto this dome?

I have noticed that if I take an HRDI file into Photoshop and resize it and save it as an HDRI, the image looks exactly the same when loaded onto a Daz infinite dome, other than depending on if it is resized larger or smaller the smaller file has a noticeable loss in quality and detail definition but the dome images are the same size.

What is odd is that the relative size of the objects (i.e. the sun or moon etc.) in the HDRI "projection" (if it is a projection) is still the same size!

Is the infinite dome always the same size?

The infinite dome can be rotated on all axis but there is not a resize slider. It seems the infinite dome cannot be translated either, only the finite dome can be translated. That might have solved my dilemma. If I move my figures/objects in the scene further away or closer to the sun/moon, then it distorts the sun/moon so they become oblong and misshapen.

If the infinite dome is a projection, then this would affect the finite dome in different way.

Depending on if the HDRI file is a projection. How is the HDRI file transferred to the finite dome from the infinite dome? Is the image refracted like though a piece of glass from the infinite dome outside to the finite dome inside or is it projected to the finite dome and then onto the infinite dome also? There is a size distortion between the infinite dome to the finite dome. The finite dome shows the sun/moon objects of the infinite dome smaller when inside of it.  Is it a projection from the center of the scene out or projected from the outside dome in?

If this is a projection, how do I adjust the "projector" to make the image/dome size smaller or larger if it is not a projection how to I scale the image wrapped around the dome so the sun/ moon is closer (smaller) or further away (larger)? (I am not referring to the sun/sky only option. This is regarding HDRI skies.)

I bought a pack TerraDome and in the promo pics it shows the sun smaller, but I can't figure out how to resize the sun. I don’t want to make it half as small I want to be able to gradually make it smaller or larger, so it fits precisely into my scene the way I need it.

Any answers to these questions are greatly appreciated.

You can resize the finite dome but that does not affect the image "projected" onto the dome, it remains constant. It seems the image on the finite dome is about half the size of the infinite dome. Do I have to edit a parameter in the HDRI file itself to change the initial dome size?

And if the dome size remains constant, what exactly does the environment lighting resolution slider do especially regarding how many megapixels the HDRI file is? Does it raise and lower the megapixels of the file itself or does it lengthen the ray tracing paths of the HDRI light effect?

If the dome is always the same size, then that would explain why more megapixels makes a more detailed image, but you would think that a larger image would make a larger dome size. This does not seem to be the case. This again leads me back to the question how do I resize the infinite dome or use the finite dome to obtain the same effect? This all boils down to, how do I resize the HDRI sun/moon?

Thanks in advance for any help on this. (really confused) 

Post edited by RexRed on

Comments

  • nemesis10nemesis10 Posts: 3,490
    RexRed said:

    This thread is created so people can get HDRI questions answered.

    And wow, do I have some questions!

    For instance, 

    Is HDRI a "projection"? Is it projected from the infinite dome into the scene or from the center of the scene to the infintie dome and then light/color bouncing off the infinite dome back into the scene?

    Is the HDRI map simply laid/stretched upon/around an "infinite/finite dome" or is it something that is projected onto this dome?

    I have noticed that if I take an HRDI file into Photoshop and resize it and save it as an HDRI, the image looks exactly the same when loaded onto a Daz infinite dome, other than depending on if it is resized larger or smaller the smaller file has a noticeable loss in quality and detail definition but the dome images are the same size.

    What is odd is that the relative size of the objects (i.e. the sun or moon etc.) in the HDRI "projection" (if it is a projection) is still the same size!

    Is the infinite dome always the same size?

    The infinite dome can be rotated on all axis but there is not a resize slider. It seems the infinite dome cannot be translated either, only the finite dome can be translated. That might have solved my dilemma. If I move my figures/objects in the scene further away or closer to the sun/moon, then it distorts the sun/moon so they become oblong and misshapen.

    If the infinite dome is a projection, then this would affect the finite dome in different way.

    Depending on if the HDRI file is a projection. How is the HDRI file transferred to the finite dome from the infinite dome? Is the image refracted like though a piece of glass from the infinite dome outside to the finite dome inside or is it projected to the finite dome and then onto the infinite dome also? There is a size distortion between the infinite dome to the finite dome. The finite dome shows the sun/moon objects of the infinite dome smaller when inside of it.  Is it a projection from the center of the scene out or projected from the outside dome in?

    If this is a projection, how do I adjust the "projector" to make the image/dome size smaller or larger if it is not a projection how to I scale the image wrapped around the dome so the sun/ moon is closer (smaller) or further away (larger)? (I am not referring to the sun/sky only option. This is regarding HDRI skies.)

    I bought a pack TerraDome and in the promo pics it shows the sun smaller, but I can't figure out how to resize the sun. I don’t want to make it half as small I want to be able to gradually make it smaller or larger, so it fits precisely into my scene the way I need it.

    Any answers to these questions are greatly appreciated.

    You can resize the finite dome but that does not affect the image "projected" onto the dome, it remains constant. It seems the image on the finite dome is about half the size of the infinite dome. Do I have to edit a parameter in the HDRI file itself to change the initial dome size?

    And if the dome size remains constant, what exactly does the environment lighting resolution slider do especially regarding how many megapixels the HDRI file is? Does it raise and lower the megapixels of the file itself or does it lengthen the ray tracing paths of the HDRI light effect?

    If the dome is always the same size, then that would explain why more megapixels makes a more detailed image, but you would think that a larger image would make a larger dome size. This does not seem to be the case. This again leads me back to the question how do I resize the infinite dome or use the finite dome to obtain the same effect? This all boils down to, how do I resize the HDRI sun/moon?

    Thanks in advance for any help on this. (really confused) 

    Let's start with "I have noticed that if I take an HRDI file into Photoshop and resize it and save it as an HDRI, the image looks exactly the same when loaded onto a Daz infinite dome, other than depending on if it is resized larger or smaller the smaller file has a noticeable loss in quality and detail definition but the dome images are the same size.".  
     

    No, an HDRI is not like a conventional image like a standard image.  What makes it magical is that there is added luminance that "lights" up the scene with the image like a sky dome as an added benefit.  When you alter it in Photoshop or Gimp, you reduce those luminance levels as you manipulate the image to fit into the human visual range.

    This two questions can be answered the same way: 

    "Is HDRI a "projection"? Is it projected from the infinite dome into the scene or from the center of the scene to the infintie dome and then light/color bouncing off the infinite dome back into the scene?

    Is the HDRI map simply laid/stretched upon/around an "infinite/finite dome" or is it something that is projected onto this dome?"

    The HDRI map is closer to an infinite map projected onto an infinite dome; it something closer to the actual sky which seems like a two dimensional structure but is actually more complex than that. 

     

    "Is the infinite dome always the same size?

    The infinite dome can be rotated on all axis but there is not a resize slider. It seems the infinite dome cannot be translated either, only the finite dome can be translated. That might have solved my dilemma. If I move my figures/objects in the scene further away or closer to the sun/moon, then it distorts the sun/moon so they become oblong and misshapen."

    Yes, the infinite dome is infinite so it pretty much is one size.

    "If the dome is always the same size, then that would explain why more megapixels makes a more detailed image, but you would think that a larger image would make a larger dome size. This does not seem to be the case. This again leads me back to the question how do I resize the infinite dome or use the finite dome to obtain the same effect? This all boils down to, how do I resize the HDRI sun/moon?"

    This is that division between the the HDRI as a light source vs a sky dome.  The resolution determines the resolution of the light that lands on elements in your scene as well as the crispness of your background.  Since the dome is infinite, the higher resolution doesn't make a bigger dome, it makes a crisper dome.  So How do replicate those gigantic suns an moons like orestes-iray-hdri-skydomes--oblivion ,  time to play with your camera's focal length.  The default camera is an approximation of a "normal lens" at 50 mm.  If you change the focal length, you can make two objects that are far apart look close together such as


     

    So that is how you "resize" the sun or moon.

  • RexRedRexRed Posts: 1,374

    [quote=Nemesis] Yes, the infinite dome is infinite so it pretty much is one size. [/quote]

     

    I don't remember studying infinite domes in geometry but it seems like it is a dome that contains three straight lines that are infinite XYZ.

    But it seems the term "infinite dome" is any oxymoron... The way a dome is shaped it must fall off at some point and begin to slope down...

    That is unless the dome employs some sort of fractal algorythm that keeps rewriting itself no matter where you position the camera.

    Can you elabporate on that more Nemesis? 

     

  • RexRedRexRed Posts: 1,374
    edited March 2020
    nemesis10 said:
    RexRed said:

     

     

    Yes, the infinite dome is infinite so it pretty much is one size.

     

     

    I don't remember studying infinite domes in geometry, but it seems like it is a dome that contains three straight lines that are infinite XYZ vectors.

    But it also seems the term "infinite dome" is any oxymoron or an abstract at best... The way a dome is shaped it must fall off at some point and begin to slope down...

    That is unless the dome employs some sort of fractal algorithm that keeps rewriting itself no matter where you position the camera.

    Can you please elaborate on that more Nemesis? 

    Post edited by RexRed on
  • nemesis10nemesis10 Posts: 3,490

    The mathematical description doesn't really apply since the infinite HDRI is not a piece of geometry.  A better model is the real sky when you want to take a picture of a person with a large moon looming over their shoulder. You don't physically manipulate the real moon and move it to the right position. You pose the person and then choose the right focal length that makes the moon seem large.  There is no geometry to adjust; the infinite dome is boundless so there is no curvature that you can see.

  • RexRedRexRed Posts: 1,374
    edited March 2020
    nemesis10 said:

    The mathematical description doesn't really apply since the infinite HDRI is not a piece of geometry.  A better model is the real sky when you want to take a picture of a person with a large moon looming over their shoulder. You don't physically manipulate the real moon and move it to the right position. You pose the person and then choose the right focal length that makes the moon seem large.  There is no geometry to adjust; the infinite dome is boundless so there is no curvature that you can see.

    I am not sure I will ever understand this like I would like to.

    I think what helps my understanding is the sky cover with sun/moon is seemingly infinite compared to a person or few objects in a scene. Just as the universe is seemingly infinite compared to the earth's atmosphere. This is probably why the camera can adjust the size with the focal length. Perhaps the same idea as the horizon always looks flat because the earth is infinitely flat compared to our human perspective, but a camera lens effect can make the earth's horizon look curved... 

    Post edited by RexRed on
  • nemesis10nemesis10 Posts: 3,490
    RexRed said:
    nemesis10 said:

    The mathematical description doesn't really apply since the infinite HDRI is not a piece of geometry.  A better model is the real sky when you want to take a picture of a person with a large moon looming over their shoulder. You don't physically manipulate the real moon and move it to the right position. You pose the person and then choose the right focal length that makes the moon seem large.  There is no geometry to adjust; the infinite dome is boundless so there is no curvature that you can see.

    I am not sure I will ever understand this like I would like to.

    I think what helps my understanding is the sky cover with sun/moon is seemingly infinite compared to a person or few objects in a scene. Just as the universe is seemingly infinite compared to the earth's atmosphere. This is probably why the camera can adjust the size with the focal length. Perhaps the same idea as the horizon always looks flat because the earth is infinitely flat compared to our human perspective, but a camera lens effect can make the earth's horizon look curved... 

    I think you will end up going in circles if you treat the infinite dome as a piece of geometry bound by all the rules of geometry such as curvature.  For example, no matter how you look at the stars, you will never see a curvature effect on the known universe since the universe is infinite; ironically, you can see back in time but tht is not germane to our discussion. The central thing is that an HDRI is not a skydome  with horizons, depth etc... it is more an ambient boundless space so there isn't some sort of geometric rules that can be applied to resize infinity etc...  The universe is not seemingly infinite from the earth's atomsphere; it actually is infinite....  

  • RexRedRexRed Posts: 1,374
    edited March 2020
    nemesis10 said:
    RexRed said:
    nemesis10 said:

    The mathematical description doesn't really apply since the infinite HDRI is not a piece of geometry.  A better model is the real sky when you want to take a picture of a person with a large moon looming over their shoulder. You don't physically manipulate the real moon and move it to the right position. You pose the person and then choose the right focal length that makes the moon seem large.  There is no geometry to adjust; the infinite dome is boundless so there is no curvature that you can see.

    I am not sure I will ever understand this like I would like to.

    I think what helps my understanding is the sky cover with sun/moon is seemingly infinite compared to a person or few objects in a scene. Just as the universe is seemingly infinite compared to the earth's atmosphere. This is probably why the camera can adjust the size with the focal length. Perhaps the same idea as the horizon always looks flat because the earth is infinitely flat compared to our human perspective, but a camera lens effect can make the earth's horizon look curved... 

    I think you will end up going in circles if you treat the infinite dome as a piece of geometry bound by all the rules of geometry such as curvature.  For example, no matter how you look at the stars, you will never see a curvature effect on the known universe since the universe is infinite; ironically, you can see back in time but tht is not germane to our discussion. The central thing is that an HDRI is not a skydome  with horizons, depth etc... it is more an ambient boundless space so there isn't some sort of geometric rules that can be applied to resize infinity etc...  The universe is not seemingly infinite from the earth's atomsphere; it actually is infinite....  

    One thought, perhaps the domain of creation itself can make the universe seem finite and small... It is all a matter of relativity. :)

    Microbial particles would also see the atmosphere as infinite, the same atmosphere where we regularly resize things and translate them around.

    The question is, how do you resize infinity? 

    Post edited by RexRed on
  • nemesis10nemesis10 Posts: 3,490
    RexRed said:
    nemesis10 said:
    RexRed said:
    nemesis10 said:

    The mathematical description doesn't really apply since the infinite HDRI is not a piece of geometry.  A better model is the real sky when you want to take a picture of a person with a large moon looming over their shoulder. You don't physically manipulate the real moon and move it to the right position. You pose the person and then choose the right focal length that makes the moon seem large.  There is no geometry to adjust; the infinite dome is boundless so there is no curvature that you can see.

    I am not sure I will ever understand this like I would like to.

    I think what helps my understanding is the sky cover with sun/moon is seemingly infinite compared to a person or few objects in a scene. Just as the universe is seemingly infinite compared to the earth's atmosphere. This is probably why the camera can adjust the size with the focal length. Perhaps the same idea as the horizon always looks flat because the earth is infinitely flat compared to our human perspective, but a camera lens effect can make the earth's horizon look curved... 

    I think you will end up going in circles if you treat the infinite dome as a piece of geometry bound by all the rules of geometry such as curvature.  For example, no matter how you look at the stars, you will never see a curvature effect on the known universe since the universe is infinite; ironically, you can see back in time but tht is not germane to our discussion. The central thing is that an HDRI is not a skydome  with horizons, depth etc... it is more an ambient boundless space so there isn't some sort of geometric rules that can be applied to resize infinity etc...  The universe is not seemingly infinite from the earth's atomsphere; it actually is infinite....  

    One thought, perhaps the domain of creation itself can make the universe seem finite and small... It is all a matter of relativity. :)

    Microbial particles would also see the atmosphere as infinite, the same atmosphere where we regularly resize things and translate them around.

    The question is, how do you resize infinity? 

    From my grad school days, I have known far too many math grads who love the boundlessness of the infinite.  As for your problem, you can use the HDRI of your choice to light your scene, and then use your manipulated image with the enlarged sun or moon as a backdrop Daz Studio> Render Tab> Render Environment.  

  • RexRedRexRed Posts: 1,374
    nemesis10 said:
    RexRed said:
    nemesis10 said:
    RexRed said:
    nemesis10 said:

    The mathematical description doesn't really apply since the infinite HDRI is not a piece of geometry.  A better model is the real sky when you want to take a picture of a person with a large moon looming over their shoulder. You don't physically manipulate the real moon and move it to the right position. You pose the person and then choose the right focal length that makes the moon seem large.  There is no geometry to adjust; the infinite dome is boundless so there is no curvature that you can see.

    I am not sure I will ever understand this like I would like to.

    I think what helps my understanding is the sky cover with sun/moon is seemingly infinite compared to a person or few objects in a scene. Just as the universe is seemingly infinite compared to the earth's atmosphere. This is probably why the camera can adjust the size with the focal length. Perhaps the same idea as the horizon always looks flat because the earth is infinitely flat compared to our human perspective, but a camera lens effect can make the earth's horizon look curved... 

    I think you will end up going in circles if you treat the infinite dome as a piece of geometry bound by all the rules of geometry such as curvature.  For example, no matter how you look at the stars, you will never see a curvature effect on the known universe since the universe is infinite; ironically, you can see back in time but tht is not germane to our discussion. The central thing is that an HDRI is not a skydome  with horizons, depth etc... it is more an ambient boundless space so there isn't some sort of geometric rules that can be applied to resize infinity etc...  The universe is not seemingly infinite from the earth's atomsphere; it actually is infinite....  

    One thought, perhaps the domain of creation itself can make the universe seem finite and small... It is all a matter of relativity. :)

    Microbial particles would also see the atmosphere as infinite, the same atmosphere where we regularly resize things and translate them around.

    The question is, how do you resize infinity? 

    From my grad school days, I have known far too many math grads who love the boundlessness of the infinite.  As for your problem, you can use the HDRI of your choice to light your scene, and then use your manipulated image with the enlarged sun or moon as a backdrop Daz Studio> Render Tab> Render Environment.  

    Yes, this was what got me editing the files in Adobe Photoshop. I found I can open two different HDRI files in Photoshop and copy parts out of one and paste them into the other and then save the file in its native format and I don't think it loses any of the dynamic range as long as it is saved as an HDRI. What are your thoughts on that?

  • WendyLuvsCatzWendyLuvsCatz Posts: 38,515
    edited March 2020

    any spherically mapped image can be an iray dome HDRi not just photographs

    it simply means the lighting is image based shining or casting shadow from the wrapped around sphere onto the object/s in the centre of it.

    DAZ studio iray render engine requires it to be in HDR format to work (it blows out otherwise) but I used IBL spheres with panoramic textures in other software and 3Delight Uberenvironment for years prior and it's the same principle.

    I found just saving any image in HDR format in Gimp actually works, just make sure it's spherically mapped or you get a seam.

    pro tip, grab all your old Uberenvironment, Reality, Poser IBL and other tiff, tga panoramas and save them in Gimp to HDR

    Post edited by WendyLuvsCatz on
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