how to shoot chrome ball

Camera Information:

Use any camera that will allow you to: 1) Lock the focus,2) Lock the white balance 3) Lock the F-stop (Depth of Field),and 4) disable the in-camera “automatic” color correction,sharpening, saturation, etc. You want and need pure, clean,and consistent exposures.

It is also It is also very helpful/advisable to use a cable release whenshooting to minimize camera movements. Similarly, if yourcamera has a mirror lock-up feature, then use if you will betaking long exposures... anything slower than 1/30 of a second.

Digital SLR cameras are certainly the most convenient,but are not required.

Tripods / Monopods / C-stands:

YYou will need to shoot with your camera on a tripod and your chrome ball on a steady surface,monopod, or C-stand to hold it in place. If it is a windy day, be sure to tape your ball to its standand also to weigh down your C-stand with sandbags or even a camera bag to help keep thingsperfectly still while shooting.

If you later find out there was some movement, be sure to use the de-ghosting feature of your HDRcreation software to minimize any fuzziness that may occur when combing the multiple exposuresto make the final HDR file.

Raw or JPEG Capture? Raw or JPEG Capture?

JPEG will be faster to shoot and smaller file sizes and is better for fast moving orfast changing environments. However, JPEGs are only 8-bits, so it is critical that you get yourcolor balance correct before you start shooting.

RAW files are generally 12 or 14-bits and are bigger files and slower to save. However, with the gainin color information per channel, it will retain much more shadow, highlight, and color temperatureinformation than JPG files. Even though it is highly advisable to determine your correct color balancebebefore shooting, RAW allows you to change/correct your color balance AFTER you have already takeneach of the photos. Moreover, RAW processing applications will also allow you to preserve highlightsand shadow information that would normally be gone in an 8-bit file. I highly recommend RAW for everything. Unless you are NOT familiar with how to post-processRAW files. If that is the case, then you might shoot JPGs to be safe or if you’re in a hurry.

by Kirt Witte - [email protected] of Visual Effects / Savannah College of Art & Design

How to shoot a chrome ball for HDRI

Where do I put the ball before I shoot it?

Put the ball in the approximate location your CG object or character will be in your final plate.

What side of the ball do I photograph?

You need to shoot in the same direction that your film or video camera will be shooting.It is preferable to shoot your HDRI ball shots either right before or right after your principlephotography has occurred.

XThis is just right. Small reflection will be

easy to remove from image.Definitely too close. Reflection is taking up

a huge percentage of the ball.

How close should I be to photograph the ball?

As far away as possible to minimize your reflection. If you are too close, this will cause much moredigital retouching needed later and more importantly, you could throw off the lighting informationin your CG scene because your reflection (and bright red shirt!) will affect the final lightingproduced by the HDR.



X

How much of the viewfinder/image should I fill with the ball? Does it matter?

It definitely matters. You want to fill your viewfinder/frame with as much of the ball as you can without cropping into the ball. (You will fine tune the crop later in post.) You want to get thebest capture possible and filling the frame will ensure the best results. Otherwise, you may onlyend up with the ball only using 10% of your pixels!

X XMake sure the camera is level with the ball.

Do I need to shoot level with the ball?

YES! (if at all possible.) Sometimes shooting at an angle cannot be avoided depending on your project.



So, then take your images and generate your HDR (Radiance) file in the application of your choice.Be sure to save it in 32-bits! If you save as a JPEG,you will lose most of your data and it will be nearly useless.

NOTE - If you have exposures that are pure black (underexposed) or are pure white (overexposed),then do NOT try to use those images when generating your HDR files.

What application(s) can I use to make an HDR file?

Photoshop, Photomatix Pro, Picturenaut, HDRshop, etc.

How many shots will I need?

Once you determine you normal baseline exposure, then you will generally be bracketing your exposuresabove and below that normal exposure. It also depends on how contrasty the scene is that you are tryingto capture and also depends on how critical the color/exposure data is to your final project. Timeconstraints are also commonly a factor.

If you shoot JPEG, then you will need to bracket in 1 F-stop (EVs) increments. If you are shooting in RAW,then then you can shoot less images in 2 F-stop increments. Typically, I shoot -2, N, +2 for most of my HDRs.However, to capture the same amount of information in JPEG, you would need to shoot:-3, -2, -1, N, +1, +2, +3 or maybe even a little more than that.



Next...

Open your cropped ball HDR filein a program (ie: HDRshop) that willallow you to “unwrap” the ball image.

In HDRshop, go to IMAGE -->PANORAMA -->PPANORAMIC TRANSFORMATION

Then pick :Mirrored Ball for the INPUTthen pick LATITUDE LONGITUDE for theOUTPUT format and set the destinationimage to New Image. Leave it at (or set it to)an aspect ratio of 2:1

NOTE - There are other utilities out therethat wthat will also do this. HDRshop was the“original” and it is free for non-commerical usage.

http://www.HDRshop.com

Then take your HDR file and crop it right to thevery edges of ball itself. Do NOT crop into the ballitself. As for where to crop the bottom? Try toimagine where the bottom of a perfect circlewould be and crop there.

Next...

Check the image siCheck the image size: If it is something like 1032 pixelstall and 1024 pixels wide, then I recommend resizingit with “contstrain proportions” turned off. Make the balla perfect square at 1024 pixels (for example).

Knowing these dimensions makes the next few steps easier as well.



Retouch the image as needed to removethe shadow of the tripod, any large blackareas or pinched areas, etc. You must beworking with an image editor that workswith 32-bit files for this to work correctly.

When finished, use the offset filter torreturn the image back to its originalposition. (This step is not critical, just ahabit of mine to be consistent.)

Save your file!!

You are now ready to import yourHDR panorama into almost any 3D program.

WWasn’t that easy? Enjoy your lighting!

NOTE: Yes, there is much more to all ofthis than can be covered here. I can also suggest taking a look at my FAQ on HDRI located at:http://employeepages.scad.edu/~kwitte/html/HDRI.html

You will notice that the edges of the imageare “pinched” and has artifacts.This is not good, but can be easily fixed.

In Photoshop, use the offset filter to slideyour image 50% horizontally. 512 pixels ifyour Latitude Longitude file is 1024 pixelswide.

NOTE: There is another method of fixingthis with a 2nd or even 3rd chrome ball.BBut that is not covered in this particularhandout.



how to shoot chrome ball

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