What is the optimal pixel-size for HDRI in DAZ?

Lonesome Cowboy

Hallo,
the new possibility with the new hdri-creator-tool offers the question about the size of a daz-compatible hdri.

How large should a hdri / .exr file be and what are the optimal pixel dimensions for it?
I created an .exr with 12000 x 8000 pixel and it was nearly 900 MB large !!!
This is too much: For my harddisk and for download (the disk storage on internet-download-places)

Which are the optimal dimensions of such an image?
12000 x 6000? still very large, but when you render it too small (the base settings of the tool are 4000x2000), it's getting pixelated.

Today i experimented with 8000x4000px and 10000x5000px and it seems that 8000x4000 works, but 10000x5000 is better

What is the optimal compromise?

Thanks

 

https://drive.google.com/file/d/1GDyx1rEmxFGv2FScBGHMqDAXcuSJkbsI/view?usp=sharing
https://drive.google.com/file/d/1E_keYWgBhzWolcyuQ7nd337EqwfR_IpR/view?usp=sharing

 

tfis

Lonesome Cowboy said:

...

What is the optimal compromise?

 

Why not buying a new HD?

jbowler

Lonesome Cowboy said:

What is the optimal compromise?

There isn't one because it depends on exactly what you do with the HDRI.  If the HDRI is only used for lighting (Draw Dome "off") then the DAZ default, if I understand the "Environment Lighting Resolution" correctly, is just 512 pixels; 0.5k, but that does give 128k separate light points round the dome (64k about the horizon).  Normally that's adequate and I have lowered the resolution to 128.

If you are drawing the dome then the sky is the limit ;-)  Normally in Studio it isn't possible to have the HDRI in focus; the background has to be out of focus.  If it is at infinity that's normally not a problem but if it has stuff like trees or walls then it is essential to turn on Depth of Field and make sure the background objects are well outside the farthest focus.  This is because a 16k HDRI barely has enough pixels for adequate focus with anything but the lowest resolution renders and/or the widest lenses.  Here's a table of HDRI "k" values by render pixel width and (35mm) focal length.  These numbers give 1:1 HDRI pixels per render pixel:

Lens(mm)	35	50	65	80	125
Render(pixels)	54	40	31	25	16	FoV
1024	6.6	9.1	11.6	14.2	22.0
1280	8.3	11.4	14.5	17.7	27.5
1920	12.4	17.0	21.8	26.6	41.2
3840	24.8	34.1	43.6	53.2	82.4

The FoV row is in degrees.  DoF mitigates this by making objects in the scene which approach the background out-of-focus.

I created an .exr with 12000 x 8000 pixel and it was nearly 900 MB large !!!

It's not compressed.  Poly Haven's 16k HDRIs come in around 3-400Mbyte, but EXR 16k HDRIs rendered by Studio are 1.5GByte.  All these files render the DAZ "Environment" pane UI almost unusable on my system; every time I click on it Studio hangs for several seconds reloading the HDRI.  Use lower resolution to build the scene and swap out to the high resolution only when ready for the final render.

Lonesome Cowboy

Thank you very much for your answer, but my problem was or is the following:

a) i created first (with the tool) in 4000 x 2000 and the result was very very pixelated

b) later i tried 12000 x 6000 and it was much better but still pixelated. The Script scaled down to 10000 x 6000, so i tried next 10000 x 5000 because of the 2:1 factor

The exr-size was now very very large (betwenn 500 and 900 mb)

This is too much.

Now i want to know

a) what dimensions i have to use that it is no pixelated any more and
b) what to do so that the exr is not so large. Is there an exr-compressor available?

Thanks

jbowler

I'm not sure this will help the OP but it is in context and may help others.  Using a DAZ Studio originated 16K HDRI (i.e. 16384 px wide, 8192 px high) in EXR format:

Original HDRI: 1,538,112,022 bytes

1. Open with the GIMP and "Export As..." Radiance format (use the extension .hdr).  The result is 536,870,978 bytes in size, 35% of the original size.  NOTE: save as ".exr" is also possible but the GIMP does not produce a compressed EXR so it ends up the same size, see (4) below.
2. Open with PhotoShop, save as EXR and choose your poison.  I used wavelet compression and it gave me a 557,135,200 EXR file, 36% of the original size.
3. Open with PhotoShop, save as HDR (Radiance format), there are no options.  This gave me a 439,739,078 byte .hdr, 29% of the original size.
4. Open the .hdr from (1) in the GIMP and "Export As..." with extension .exr.  The result is 481,767,551 bytes, 31% of the original size.  I suspect this has gone through two steps of compression so I wouldn't reccommend this approach.  There is probably some mysterious way of persuading the GIMP to compress an EXR when it is exported by I don't know what it is.

All these versions load just fine in DS 4.21.1.45 and I can detect no difference between them onscreen (using a 1040mm lens - 16x the standard).

I see no pixelation:

So that is a 16k HDRI (although the "starry sky" is, in fact, a lower resolution PA HDRI, I think it was 8k) and a 1040mm lens, 512x512 dimensions.  It has a FoV of 2 degrees which would, at 512px, correspond to a 93K HDRI and means that the image spans 90.2x90.2 pixels of the (16K) HDRI.  There might be some aliases on the "starry night" background, but those might be in the original PA product or they might be an interaction because I used bicubic to scale the image(x4) to check for aliases (I don't have a program which will resample using sinc at present.)

It appears out of focus, as it should.  Indeed "out of focus" is substantially the same as smoothing and smoothing is the result of upsampling if it is done correctly using sinc, although I've always found bicubic produced indistinguishable results.  I don't know how Iray handles the under-resolution HDRI but I assume it does resample it with some approximation of sinc rather than just sampling with a suitably wide Gaussian (which would produce aliases though very small ones.)

DoF is your friend :)

Lonesome Cowboy

thank you very much, i will make a few tests in gimp and then i will see, whether my old PS version CS 5.5 can handle hdr files :-)