View Full Version : Using HDR images

06-27-2005, 08:54 PM
Im using a HDR image to light my scene and the output is very grainy.

Here are the steps i used maybe I missed something.

turned off all lights and Ambient light.
Loaded the images in "Images World"
Turned on radiosity
turned on Shading noise reduction
and set radiasity to Background only.

Oh ya i hit F9.

Also when I use .jpg it works no grain at all but the final render dosnt look as good.

06-27-2005, 09:11 PM
What is your radiosity setting (rays per evaluation). Setting this to a higher number will probably reduce or eliminate the grain but of course, your render times will be higher.

06-27-2005, 09:17 PM
You can try blurring your HDRI a bit (with HDR shop or HDRIE, both freeware, or Photoshop CS2 if you have it). This will also make it render faster.
Also make sure the HDRI resolution is reasonably high, like 1024+.
If there are too many contrasty small features in your HDR image, both these things will help.

If it's more blotchy than grainy, try increasing your 'rays per evaluation'.


06-27-2005, 09:50 PM
ok I initially did it at 6x14 (or somthing).

I went to PS CS2 and resaved the file as a .hrd (it already was a hdr file but just to make sure) and the I went up to 16x33.

Its still grainy...

Im on a mac Ill have to try it at home on my PC to make sure.

Unles you guys have any more ideas?

06-27-2005, 09:53 PM
Can you post a image of the results you are getting?

06-27-2005, 10:00 PM
here is the render

06-28-2005, 01:25 AM
You can also blur the HDRI in Lightwave in the image editor and control the amount of blur without changing the actual photo. Image editor, processing tab, add filter, blur.

Captain Obvious
06-28-2005, 04:59 AM
According to Worley's "Art of Noise" text, a good way to reduce noise is to create a second version of the HDR image, in lower resolution and blurred, and use the original for reflection maps.

06-28-2005, 08:33 AM
One thing I was trying to do was use an image for hdri but not have it render in the final output..

So I discoverd that using imageworld but then loading in a 0.0.0 black image into the background then saving the resulting render with alpha aka 32bit images will preserve the shading you want but also let you take it into a compositing program. "See attached". Tardis model thanks to Colkai (Do user search here for him he rocks!)

Thomas M.
06-28-2005, 08:38 AM
Use a small .hdr (like 128x64 in lat./long.) and take care that you block out the sun and replace it with a LW light. That should help you to get rid of the white speckles. The other grain is related to the LW radiosity settings.


06-28-2005, 04:20 PM
yes, you can use a small hdr if you don't want to see it in the background, but the blur is especially important. When you say 16x4 i guess you are talking about inches...? The important thing is the pixel resolution, BTW. If you don't want to see the backgound, i would try a 512pixel resolution (long), and blur the hdr in PS CS2, which apparently you have. But you can easily gow lower res too, if you blur it a lot. I was experimenting with blur on hdrs yesterday, and love having the blur choices available in CS2. You can also make selections and adjust the exposure, which helps a lot toward getting a good result.

I haven't had any problem using the light source in an HDR, as long as you don't want hard shadows, and with CS2 you can select and pump up the exposure for your light areas which helps too. You can also clone lights and glows from other HDRs and make your own GI source that fits your criteria. It pays to experiment with this, its a very powerful tool, even if it doesn't have brushes for HDR yet.

If you map it to a luminous dome/sphere, then you can see in layout exactly where the light is positioned and what might be affecting your scene. A lot of pixelated detail can also cause speckling (hence the blur).


06-28-2005, 05:22 PM
You guys do know that you don't need to edit the image in another app and save it under a different file name, you can just add an FP blur on the image processing tab in Image Editor to blur an image without having to alter it?


06-28-2005, 08:02 PM

in the image editor [ctrl+F4], go to the "Processing" tab and add HDR exposure, a bit down the list. Full Precision Blur as well as Full Precision Gamma can be useful as well, I see the blur is mentioned here but the gamma increases or reduces the i think the *Value of the middle tones.

Cut and paste from the manual; also see google the issue is well covered here, CGtalk, Spinquad.

"Full Precision Gamma"

Display devices have a non-linear relationship between pixel values
and physical light intensity—they do not excite the display phosphors
linearly. This non-linearity must be compensated for to correctly
reproduce intensity. The Gamma Correction value is the exponent value
in the correction formula and determines how to convert pixel values to
light intensity. The default, 2.2, is a common value used on images bound
for video, but is not necessarily the optimum value.

"HDR Exposure"

This filter normalizes high dynamic range (HDR) images for using as
image maps and HDR output for displaying in applications that are not
HDR-savvy. The intensity mapping is non-linear, similar to the light
response process in the human eye.
This filter processes the HDR output created by radiosity renders into
better-looking, brighter pictures. It does this without impacting the
accuracy of the lighting simulation, which can happen if you add
ambient light or crank up lights unrealistically. It is really an essential
part of the camera simulation, for a perfect digital camera. (The Virtual
Darkroom filter is similar, but more complex. It simulates the two-stage
process of film response to light, and print emulsion response to
projection through the film negative.)
Although you can add this filter on the Image Editor, it is of limited
use there and more useful as an Image filter on the Processing tab of the
Effects panel. This is mainly because most images you load are not HDR
images, so pre-processing is not necessary and normal gamma should
probably be used, if necessary. Moreover, if you do load an HDR image,
it’s probably because you want the extra data. (Using the HDR Exposure
filter will eliminate some, if not all, of the extra data.)

The Input Dynamic Range is an informational display showing the
High and Low pixel-intensity values encountered in the last processed
image. Note that when the panel first appears, this information is not yet

If you do not want the filter applied to the Full Image, set the
Exposure Apply pop-up menu to Foreground to apply it only to scene
items or Background to affect only the background (i.e., where your
alpha would be black).

The White Point is the input intensity considered to be the hottest
white. Anything above this will be the same white in the output. This
control is overridden by the Auto-Iris option, which sets the white point
based on the actual input image data. Adjusting the white point is similar
to cranking down an iris on a film camera to limit how bright parts blow
out in a photograph.
The Black Point, expressed as a percentage of the nominal black
point (1/255), is the darkest non-black pixel level in the input image that
will be preserved. Anything darker will come out black. The Auto-
Exposure option overrides Black Point by using the actual image data to
determine a black point in the incoming data. Lowering the black point is
similar to increasing the exposure time for a photograph.
Once these values are set, the filter translates the incoming image
intensity—in a process very similar to gamma correction—so that the
darker colors get more of the output range than the brighter colors. In
other words, the filter changes the spacing of intensity levels so more
levels are devoted to low intensity, darker details.


06-28-2005, 08:03 PM

If its not to much trouble could someone please upload a scene thats works and i can try it and see... Maybe its just my computer.


06-29-2005, 02:36 AM
You cannot get smooth results without anti-aliasing. At least Enhanced Medium, with adaptive sampling turned off. Don't bother with PLD anti-aliasing or shading noise reduction.

Captain Obvious
06-29-2005, 09:09 AM
You cannot get smooth results without anti-aliasing. At least Enhanced Medium, with adaptive sampling turned off. Don't bother with PLD anti-aliasing or shading noise reduction.
Toby speaks the truth.

06-29-2005, 02:06 PM
One thing I've found that is helpful, especially for animations. If you bake your radiosity result to UV maps, you can pull the maps into photoshop (or other) and use a noise reduction filter on them (median is good in older versions) -- not too much but just up until you would get too much blurring in contrasty areas and lose the edge. Then you can have a very smooth monte-carlo like radiosity (with much less rendering time) and animate it very fast. You can also bake the map at a lower resolution, saving further time, and size it up, because you're going to smooth it anyway.

This works better even for stills because you can't really noise-reduce a whole frame or still without sacrificing sharpness and other qualities. When you filter just the radiosity image maps, the objects themselves remain distinct and do not blur into each other.

probably most people know this, but just in case someone doesn't. Hey, i gotta at least try to return the favor of all the advice i've received from this awesome forum.


06-29-2005, 04:02 PM

Ah the good ol' days of 3DExchange

06-29-2005, 08:12 PM