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Monday, July 26, 2010

••◊ A day at the races

Sunday was race day. Most people think of a day at the races with horses and the vertically challenged who ride them. I think of races with human horsepower...bicycles. As a retired bike racer I know what it feels like to have lungs burning and still have to keep going that last quarter-mile to the finish. Cycling is a tough sport and when it's good it's just enough to satisfy the S&M fetish most of these racers have. It's when the pain comes in manageable spurts that competition becomes fun. (OK, so I'm not fully integrated back into society).

Once a year I get to relive the glory days at our annual San Marcos circuit race. An hour around the UC San Marcos college campus drive and almost everyone's legs are logs of jello. After having to drop out of the races the first year due to an asthmatic episode I came back and won the second year, so this circuit will always hold good memories. This year I worked registration in the morning and corner #1 until late morning. That, of course, meant I had put pull out the old camera and pop off a few shots. There isn't a lot to do when you're wearing a volunteer's orange vest and watching people come by every three to four minutes - some clearly done for the day. Below are some random pics from corner #1 in the morning; the last one featuring our fearless leader Alan. I figured I better throw something in from him in this blog post so the Ranchos crew waits for me next time I get a flat.

My afternoon was *supposed* to be spent discussing upcoming projects with a film director while Clarence did a modeling shoot with Shealyn, but the director didn't make it to the meeting. So...speaking of ponies...Shealyn brought her vintage mustang down to Liberty Station. All wasn't lost. I pulled out the camera again and began shooting over Clarence's shoulder. Eventually it got to the point where Clarence just gave me the second flash trigger and we both were going full hog on the shots. Hah! Weaseled my way in to this one. Below are some mostly unplanned modeling pictures of Shealyn.

Back to techie work today. I'm still looking at 5D camera calibration and chart alignment. No shoots planned at the moment, but hopefully Shaun and Marc get back on the ball and are ready to do another comedy. The question is which business we'll be guerrilla shooting in this time? The Del Mar race track? Nordstroms? Build-a-bear workshops? Victoria's Secret? Sally beauty supply? The possibilities are endless.

Wednesday, July 21, 2010

••◊ Feeling techie, part 2: Isn't brightness supposed to be easy?

I was slightly wrong with the previous post, but for good reason. The DSC documentation is misleading for a mentally impaired monkey boy, such as myself. Going back over the documentation, the IRE levels they recommend didn't make sense. I mean what color space are we talking about here? I hate it when numbers don't make sense when I place so much trust in them everyday. When DSC says RGB does that mean sRGB, rec.709 (HD), or 601 (SD) color? Being an engineer this kept me awake at least one night until I got a grasp on what they were talking about. Charles Poynton's excellent FAQ helped to a certain degree.

Long story short, the RGB values DSC provides for the neutral tiles are straight up γ (i.e gamma) equals 0.45, so it's mostly correlated to the 601 color space. So for instance if the reflectance equals 0.18, then the IRE level = 0.18^0.45 = 46.13 IRE, 8-bit RGB value = 118. Follow with me folks because we're about to go down the rabbit hole.

The web and pretty much all computers (except the screwy Apple brand) follow an sRGB gamma curve. This calculated as follows... If the Reflectance (R) is greater than 0.0031308 then the gamma curve is calculated as E'=1.055*(R^(1/2.4))-0.055. So if the reflectance is 0.18 again then the IRE level = 46.22 and the 8-bit RGB value is 118. OK, that's pretty close to a straight up gamma at this reflectance.

Now we move on to rec.709 gamma, which is used for HDTV. If reflectance is greater than 0.018 then it's calculated as 1.099*(R^0.45)-0.099. So we end up with an IRE level of 40.9 and an 8-bit RGB value of 104.

They are all slightly different.

The 5Dm2 uses the sRGB gamma curve, which fits closely with straight γ=0.45. However it seems for using the camera in broadcast HD situations you really want to adjust the tone curve to compensate. How much...? Pretty much all footage is tweaked in post and this aspect might not be any different. Editing in sRGB and displaying in rec.709 will likely make your footage have less contrast than intended. The graph below shows how the 11 neutral tiles on the DSC Chroma du Monde Red test chart compare under each of the color spaces. See how rec.709 is quite a ways different than sRGB?

So for those of you brave enough to be reading until this point you may ask, "how much different is that little gap at the bottom of the curve?" Well, here's another graph that shows the exact amount. Anything above 5% just mentally seems like a lot. In this case there's up to 38% difference in the darker neutral tiles.

I thought, "cool, I have a test chart that will help settle my color issues out." "Oh...wait a minute, this doesn't make sense." "Oh crud, there goes my night of sleep." All this and I have yet to figure out vector scopes and color coordinates completely. I might require a melatonin pill this evening.

Sunday, July 11, 2010

••◊ Feeling techie with Chroma Du Monde (part 1)

Ben Cain over at NegativeSpaces.com sent me a raw picture of a Chroma Du Monde calibration target made for the Red camera. I know what you're thinking about the photo below...big flippin' deal - that has to be a submission for a french high end contemporary art competition, right?. Nope, this target is used to calibrate and align cameras to one standard so you can mix and match cameras and have an easier time in post with color rendition. Like most professional test targets, this is one expensive little piece of cardboard.

The Chroma Du Monde test target has a neutral gradient in the center and calibrated color swatches around the perimeter, which is exactly what we need when using the Picture Style Editor software from Canon. Now before you go thinking that you're going to download this JPEG and do your own calibration...think again. There's a reason I asked Ben to send me a raw file. The color rendition and tone curve depend on which existing picture style you start with. For instance "standard" is vastly different from "faithful" or "neutral." As it turns out, none of the existing picture styles completely align with this chart. That being said; Ben recently showed that the "faithful" picture style with saturation set to -1 comes pretty darn close to meeting the rec.709 (i.e. HDTV) chroma specifications - notice that I didn't say luma, just chroma.

The first place to start when doing any type of calibration is the tone curve since you and I are most sensitive to lightness/brightness. The tone curve essentially sets the "lightness" or luma levels to calibrated steps. To do this I used the center neutral density swatches. By tweaking the white balance in the raw file using the 18% gray border I was able to achieve very near to perfect neutrality in the center swatches (i.e. gray, no remaining color). One thing you may notice is that lighting on the target isn't perfect. The left side of the test target is brighter than the right side. At first I thought, "oh no," but then I remembered that the surrounding 18% gray border is calibrated and consistent from left to right. By measuring the average of the border near each neutral swatch I can calibrate out the lighting change across the target.

The CDM target comes with documentation that shows you where each patch should lie in within IRE levels (i.e. a measure of video signal amplitude). I'm not going to publish the exact values, but I think these pictures show the intent of the patches. Each of the Canon picture styles has a aesthetically designed tone curve applied that tweaks the lightness/brightness of the picture. The first picture below shows the neutral swatches with the "faithful" tone curve applied. The skinny lines are the IRE level reference marks (compensated for light fall off across target) and the fuzzy lines represent the light levels from each of the 11 neutral patches. The Canon profiles all have a traditional S-shaped tone curve originating from the days of film with mids bumped brighter and dark regions slightly crushed. The third picture shows what happens to the tone curve after I tweaked it in the Canon Picture Style Editor software. Ah...much better alignment, although contrast is severely lacking in the picture now, which is good or bad depending on what you're doing. Calibrated doesn't always mean good looking.

The result is a picture of the target using the new custom tone curve. Notice how the neutral swatches are much less contrast-y? In this picture I haven't tweaked the chroma (colors) yet, and yes, they are way off balance. Canon likes to crank up the yellow, red, and green saturation.

So why might this be important? Well, what it means is that you can match the Canon DSLR cameras with just about any other camera on the market, within performance limits, as long as the other camera has footage of the Chroma Du Monde target. If you're shooting with an EX1, HPX170, Red-MX, Alexa, or even Kodak film stock, you can tweak the Canon to match any of those cameras and make the 5D/7D/1D a second unit, P.O.V., or crash cam. It also makes your post production easier. As for getting good looking pictures straight out of the camera...well, not so much. My next entry about this topic will have to deal with tweaking the chroma/color to be more accurate.

Tuesday, July 6, 2010

••◊ The Sandwich

Last weekend we decided to semi-randomly film a comedy short with Shaun and Marc (a.k.a. Dave and Shane) from "Go Gadget Comedy." These two guys have great comedic timing and they had half the story written before showing up. The other half was improvised in "Whose Line is it Anyway?" style. All production and prop procurement occurred in an 8 hour period of a not-so-lazy, but fun Sunday.

This gave me a chance to try out my new shoulder rig and learn it's limitations. I need to improve the camera mount platform, add a counter weight, and improve the shoulder brace, but it worked well otherwise. Obviously in one of the scenes we were in a grocery store shooting guerrilla style, so I used a small Kodak consumer video camera (sort of like a Mino Flip) and my Marantz field recorder to get audio that could be synced up in post. They sent one poor clerk over to check us out, mostly because Shaun and Marc were in pajamas in the dairy section. Maybe the pajamas were an intimidation factor because she didn't come back.... I don't normally shop at that store, so I figured no big deal if we get kicked out.

Clarence brought over a couple cheap daylight balanced lights from Adorama. The light has a single fluorescent bulb at 5500K and a 27" soft box. They worked for fill, but would struggle as a key light. Not bad for $40. We used them for the kitchen table and outdoor interview scenes.

Post production was a major pain. It seems like between CS4 my MOTU drivers I have a very unstable editing platform. I need to upgrade to CS5 and change audio interfaces. Suffered through this one.

Friday, July 2, 2010

••◊ Playing Hookie with the Mermaids

I played hookie from work Tuesday to hang out with Clarence and a couple models at the Mermaid Salon. He lined up Shealyn Sharleen and Kelly Lee, as well as Renata Damone (not shown below). It was good to get out shooting again and exercise my shutter finger so I don't forget how it works.

The setup was fairly straight forward as shown below. Two umbrellas, one soft box, and one reflector for high-key photos. I ran the soft box one stop hot and the highlight umbrella one stop under to maintain detail. the right picture of Shealyn used this setup because of the way her hair was parted. The right picture of Kelly used the mirror image of this setup because her hair was parted to the other side.

Pictures of Shealyn...

With Kelly I tried a few different setups in the hallway and back of the business, but it just wasn't working until I tried Clarence's beauty dish. This made all the difference. I now unfortunately NEED one. The light spread was just perfect. They live up to their name. The light diagram is shown below.

Pictures of Kelly with both setups...

Lots of work to do this weekend, but more on that later.