Preparing HDR Light Probes for DAZ|Studio using HDRShop, AHDRIA and AHDRIC

 

 

This a brief tutorial on creating HDR light probes and preparing them specifically for use with DAZ|Studio and Arthur Heinz’s (Pendragon) IBL shader. This is by no means the definitive way to create HDR light probes but after much trial and error it is a method that I have found works well for me. This technique has not been approved by DAZ or Arthur Heinz, nor is it supported by them. All information provided here is the sole responsibility of the author.

 

Although this tutorial is tailored for DAZ|Studio it should also work with Bryce 6 and other applications that accept HDR Light Probes with little or no modification.

 

 

What you need to get started

 

 

Download HDRShop, AHDRIA and AHDRIC and extract the software to a folder (or folders) on your hard drive. There is no install for these programs and where you put them is up to you. You may also need to download and install the appropriate camera SDK for your camera (available from the AHDRIA website.)

 

 

Creating the HDR Image Sequence

 

Choose the setting that you wish to use as your HDR light Probe. I have found that indoor environments with several light sources make the most interesting probes.

 

Set up your reflective ball on a tripod or other suitable mount. Set up your camera so that is aiming at the ball. Connect the camera to the USB port of the computer on which you have installed AHDRIA.  Turn on the camera then start the AHDRIA application. Once the program is started press the “Connect” button to activate your camera. The application screen should look similar to the following image:

 

 

There are a lot of settings in AHDRIA, most of which you normally don’t have to worry about. One thing to do right away though is change the capture path of your images. By default it goes to the program directory. Change this to some other directory where you wish to store your images by clicking on the “Set” button and entering or browsing to your path. Also it is a good idea to select “Create time-stamped subdirectories” otherwise you may overwrite your images.

 

Use the viewfinder window in AHDRIA to center your ball in the image. If you find that the ball looks too small you can use the Zoom button in AHDRIA to zoom in on the ball, select a zoom level from the drop down list then click on the “Update Viewfinder” button. Or you can simply move the camera closer. Try to fill the viewfinder as much as you can with the ball.

 

If you find that the image in the viewfinder is all white, it means that the maximum shutter speed is too high for the current camera settings. Select a lower setting from the “Max Shutter” drop down box then click “Update Viewfinder” to see the new setting. Choose a shutter setting that leaves the image bright but not completely washed out. (see image below)

 

 

 

You may also wish to check the dark end of the scale. Select the “Preview Min. Exposure” option in Image Preview and click “Update Viewfinder.” If the image in the viewfinder is completely black select a new shutter speed in the “Min Shutter” drop down box then click “Update Viewfinder” You want your darkest image to have the barest hints of light, but not completely black. (see below)

 

 

Note that in bright environments you will probably not be able to get a very dark image on the low end. And In dark environments you will probably not be able to get very bright image on the high end. That is fine, whatever image you get at the end of the shutter scale will work fine for the environment. The important thing is that you do not get a series of completely black or completely white images in your sequence as this may affect the quality of the compiled HDR image. As an example of what can happen if there are blank images in the sequence see the images below. The image on the left had a sequence of six black images in the compile process. The image on the right had no black images compiled. As you can see there is a significant different in image quality.

 

 

Once you have the shutter speeds correctly set it is time to take the image sequence. Click the “Begin HDRI” button to start the process. I recommend standing somewhere behind the camera during the process as it will make it easier to edit yourself from the image later.

 

The program will proceed to take a series of pictures at different shutter speeds. During this process the viewfinder will be blank and the status window in the application will update as each shot is taken. The process will take a couple of minutes. When it is complete the viewfinder image will return and the status window will indicate complete.

 

 

Creating the Light Probe

 

What the program has done is create a series of Jpeg images and a text file listing exposure settings for each image.

 

 

Now we need to compile these images into our HDR image. To do this, run the AHDRIC application. This will bring up a dialog box asking for the path to the text file called “ExposureInfo.txt”

 

 

Browse to the directory where you stored the image sequence and select the file. A command window will show the progress of the conversion. Once it is done you will have a HDR image in the same directory as the image sequence.

 

 

If you don’t mind having the camera and yourself in your HDR light probe image you can move on to the next step. Otherwise you should move the camera 90 degrees around the ball and take another image sequence. You should not have to adjust any settings for the new image sequence. You can then merge the two sequences in Photoshop or other image editor by following the tutorial on the HDRI website which can be found here: http://gl.ict.usc.edu/HDRShop/tutorial/tutorial5.html

 

Once you have completed the light probe following the tutorial there are a few more steps you will need to take to make the image work with DAZ|Studio and Pendragon’s shader.

 

 

Converting the Light Probe

 

If you followed the tutorial on the HDRShop website you will now have a light probe in Angular Map format. Pendragon’s shader requires the light probe to be in Latitude Longitude format. It also requires it to be in floating point tiff format. These conversions are done using HDRShop.

 

Open HDRShop and load your light probe.

 

 

The first thing we will do is convert the image from Angular Map format to Latitude Longitude format. Go to the Image menu, Panorama, and select Panoramic Transformations.

 

 

This will bring up a Panoramic Transform dialog box. In the Source Image section select Light Probe from the Format drop down box. In the Destination Image section select Latitude/Longitude in the Format drop down box. In the destination image you can also choose the size of the new image if you want to make it different from the default.

 

 

Click OK and it will generate the new image.

 

 

Now for the REALLY IMPORTANT part: When you create the HDR image using AHDRIC the software sets the “0” aperture stop to the darkest image in original sequence. If you leave it this way it will be very dark in your rendered image in DAZ|Studio. You will need to adjust the “0” stop to be at the brightness level that you want your light probe to be. (You can change the stop level you are viewing in HDRShop by hitting the “+” and “-“ keys on the keyboard) Notice in the image above that in the lower right corner of the status bar it says “+6.00 stops” this is how bright I want my image to be. The setting you choose for your image will vary by personal taste.

 

To reset the stop so that 0 is at this setting, go to the Image menu, Pixels, Scale to Current Exposure.

 

 

The status bar will now indicate 0 stops.

 

 

With the image set to the correct brightness you can now create the tiff image.

 

Go to File, Save As. This will bring up a dialog box with a series of buttons. Under High Dynamic Range choose the Floating Point TIFF button. You will then be presented with the save as dialog where you can enter a file name and location to save your file. Name your file and hit save. You now have a HDR tiff file that you can use with Pendragon’s shader.

 

 

Using the Light Probe in DAZ|Studio

 

Now that you have you assembled and converted light probe, it is time to apply it in DAZ|Studio.

First you will need to download and install Pendragon’s shader, available here: http://www.pendragon-observatory.net/3D/projects_main.html

 

Once you have installed the shader package, open up D|S and create a scene or load a previously created scene that you wish to use. Add the ah_environment shader to your scene. If you copied the files to the default locations you will find the shader under Studio-Shaders-ah-light in the Content tab.

 

 

Once added to your scene you will see the [ah] Diffuse Environment Light object in your Scene tab.

 

 

Select the object and go to the Parameters tab. Here you are presented with several options for the shader.

 

 

Look under the “Environment Lightprobe” setting, here you will see the color selection bar. To the right of the bar is a small button with a downward arrow. Select this button and you will be able to browse to the location where you have stored your light probe. Select your light probe and it will appear in a button beneath the color bar.

 

 

Some notes on the use of the Environment shader: If you wish to use the true colors of the light probe be sure that the color bar is set to white (255 255 255)

You may also want to adjust the Environment Strength, the default of 1.00 can be quite saturated. I have found that for my light probes a setting of between 0.2 and 0.5 works well.

 

Also be sure that the Environment Channel is set to ON under the “Global Switches” option. I would also highly recommend that the Ambient Occlusion Channel be turned on for best effect.

 

Under the “Ambient Occlusion” options you may want to change the Occlusion Number of Samples from the default of 4 to something higher to remove the grainy effect. I find that 128 works well.

 

With all the settings to your liking you are ready to render your scene.

 

Happy Rendering!