Hi TCG,
If you have a permission problem, you might open the HDR in the Picture Viewer. Go to the Content Browser and drag the image into the Picture Viewer.
From there, save the file as Open EXR. The HDR (Radiance) is like a JPG compared to a Psd file. Yes, it has the largest theoretical dynamic, but also from all the HDRI formats the lowest color “resolution”. Not bad for deliveries, but not a format I would work in Photoshop with, as I wrote, comparable with jpg. BTW, the possible dynamic range is beyond anything common in nature.
As a side note, some people like to name it a 32bit format. It is a 4 times 8bit per channel format. RGBE is the short for it and the whole color is multiplied at once with the E component (also only 8bit, pretty rough if you ask me). If you like to work with quality, use Open EXR. To turn an HDR (Radiance) into any other format will NOT compensate for the color losses it had already, but any further step might be more “healthy”. (Open EXR is a 16 or 32 bit per channel format, not 32 bit per pixel as the radiance, 8 bit/c)
If you blur any image, the values will change. Low values will not go lower, higher values will not go up. The opposite is most likely the case. A slight blur might be not a big deal for these values.
Strong blurry versions of the same clear HDRI without taking care for such change, might show some suffering in values. However, the blur has a great positive side effect, as the random “rays” thrown into the scene, hit more often similar values, instead of total spikes or lows.
Please keep in mind that working with 32bit/c (per channel) and float (instead of integer—8 or 16 bit/c for example) might have the danger to set up negative values! These negative values are sometimes useful (e.g., deliveries, compositing), but not for GI renderings. (Yet, sharpening might already introduce negative values!)
If you have for example “Photomatix”, you can check your results of the blurring in the “HDR histogram”. The given contrast ratio or amount of “stops” will help you to monitor your efforts. Which will help you to overcome some concerns perhaps.
If you blur an “360º/180º” panorama, keep in mind that you have a little bit more work to do than just to blur an image. The borders will suffer. My suggestion is, use the PSD—>Filter> Other> Offset, in vertical and horizontal, with a copy of the images. Blur this as well, and use the offset the second time with the same negative numbers. Create a mask for the seam and you should get from both (Merged) then a perfect result.
What ever you do in 32bit/c, use in Photoshop the little slider on the image frame border, (perhaps you have to switch it on), and slide it to the left and to the right, to see what you have created. If I’m not completely wrong in my observation, the max left or right, is each time 20 stops (20+/20-). Which might give you an orientation how much you got after any operation (if done initially as well) Double click on that brings it to default (0). In 32bit/c mode in Photoshop you can use the color picker to see the values as well, Color Picker, where you choose the colors from)
If possible shoot your own HDRI, use a gray card to get middle values (black and white is just a relative and not useful—really). If you have a MacBeth (X-Ride) chart—even better.
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Your question—if that is a good idea. Well, depends. If you use the blurred and un-blurred in a compositing later, you need to check the values of the images. Honestly, most HDR have a very sloppy idea of the light around them. If you have no gray card in them, you have no idea what is really going on. Too many variables in the pipeline, to say it plainly. (I have discussed them all in an upcoming series).
The fact that most artists set up the materials by eyeballing, instead of measured (light meter, etc) references, might put your mind to ease, as the system works only perfect if all parts are set up 100% precisely. To care only about the HDRI and set then anything else as a variable with not fixed values, seems not a guarantee for correct values. (I go here certainly beyond typical needs, and if the monitor is not calibrated, think about variance in results by eyeballing things anyway.)
I hope these (way too short) reflections about HDRI will help you a little bit.
All the best
Sassi
