{ illuma·blogspot·com }

Friday, November 30, 2012

••◊ Matching the GoPro Hero 3 Black to a 5D mark II, part2

In the last episode I talked about matching the tone curves between the Canon 5D mark II and the GoPro Hero 3 Black Edition - two cameras that are likely to be used together on video productions.  I found that with the neutral picture style on the 5D I had to set the contrast to -3 to approximate the tone curve of the Hero 3 with Protune turned on.

With the tone curve established, this blog entry talks about how we can match the color rendition of the two cameras.  As anyone familiar with video cameras knows, no two brands of cameras look the same straight out of the box - much to the delight of a DIT's employment security!  First, let's look at the color rendition of the Hero 3 camera with the "Cam Raw" white balance versus the "5500k" white balance (I'm using an approximate 5500k light in this experiment).


As you can see (clicking on the picture to enlarge it might help) the "Cam Raw" white balance leaves the picture quite a bit desaturated from the 5500k white balance.  It appears that the folks at GoPro are doing a bit of image processing on the non-"Cam Raw" white balance settings, which makes sense if you read the instruction manual.  Let's look at the vectorscope plots to see what's really going on.



The vectorscope shows that not only is the video greatly desaturated by the "Cam Raw" setting, but GoPro also adjusted the overall color rendition because the outline of the color coordinates on the plot changed.  This tells me that they added a 3x3 matrix adjustment with normal white balance settings.  Why does this matter?  Well...because with these fragile 8-bit codecs we're using on these cameras I'm looking to do most of the camera matching in-camera.  That's where the video is still better than 8-bit.  From experience I can tell you that the 5500k white balance setting will likely be a better place to start the camera matching because it will require less adjustment later - but we'll get to that at the end of this article.

Next, let's look at the color rendition of the DSC CamAlign chart using the neutral picture style on the 5D with contrast set at -3.  The vectorscope plots below show the color rendition with the saturation set from -1 to -4.  I didn't bother with the 0 to 4 settings since the color actually gets over saturated at a setting of 0, but maybe I'll save that for a follow on article.  Notice how the overall color vectors maintain their angles, but the amplitude decreases with decreasing saturation settings?





Again, why does this matter?  Well, I'm looking for the best match of saturation with regard to the Hero 3 and the 5D.  I think at this point I may have to skip the technical explanation and just say that the best fit is a saturation value of -3 on the 5D.  How did I figure this out?  Well...that would require explaining the spreadsheet shown below in detail and who wants to read through that? (Augh!! implied...even I got a headache at one point last night)  The bottom line is that the 3x3 transformation matrix we are going to apply later in Premier Pro maintains a unity gain with the 5D saturation set to (-3).  ...and yes, that's a virtual vectorscope I wrote in Excel!


So what's the next step.  This is where things get a bit technical, but the spreadsheet shown above calculates a new 3x3 matrix that is applied to the GoPro RGB values to transform the vectorscope color coordinates you see at the beginning of this article (Hero 3 Black 5500k WB) into the 5D color coordinates with saturation set to -3.  Cutting to the chase once again; here is the matrix...

[ 1.00  -0.23   0.19]          [R-gpro]            [R-5d]
[-0.01   0.90   0.07]     x   [G-gpro]     =    [G-5d]
[-0.07   0.22   0.86]          [B-gpro]            [B-5d]

No doubt, anyone familiar with image processing is yawning about now.  So how do we implement this in Premier Pro?  Easy.  Use the Channel Mixer effect.  It implements the matrix multiply, just like we would in a pro camera that's being calibrated. See the picture below for details on how to implement the effect, but all it's really doing is the matrix multiply shown above which was calculated from my spreadsheet.  Easy, right?  Notice how now the vectorscope plot has gained the same shape as the 5d neutral vectorscope plots shown above.


Now...what happens if we have the 5D set to saturation values of -1,-2, or -4?  Isn't that going to be difficult to match?  Nope.  That's just a matter of adding a Fast Color Corrector effect in Premier Pro.  You can then scale the saturation to match saturation settings on the 5D.  Empirically, I found the following settings to be approximately correct.
  • 5D saturation -1 means set the GoPro saturation to about 120%
  • 5D saturation -2 means set the GoPro saturation to about 110%
  • 5D saturation -4 means set the GoPro saturation to about 90%
The easiest way to match the two cameras is to just set the 5D to have contrast and saturation equals (-3) and turn on Protune with a normal white balance on the GoPro.  Then you only have to apply the matrix in post and do color correction/grading from there.  I think we've been looking at scientific plots long enough.  Let's look at the test chart again.



One thing to note here is that the magenta is still a little bit off in the "After Matching" picture.  The process I've described isn't a perfect match by far, but it gets us very close to matching.  For me, perhaps sufficiently close.

The process I'll talk about in the next article involves transforming the GoPro color rendition into a semi-calibrated rec.709 color rendition.  I developed a rec.709 custom picture style for my Canon 5D mark II, which I use quite often on projects.  I know not everyone has access to fancy test charts and knows how to calculate color matrices, so I thought it would be best to start with something anyone sufficiently familiar with video editing can do.  Stay tuned for the exciting episode kids.

P.S. Don't you think GoPro should give me a free camera for this? ;)  It's just about Christmas...just saying... 

Thursday, November 29, 2012

••◊ Matching the GoPro Hero 3 Black to a 5D mark II, part1

My friend recently picked up a GoPro Hero 3 Black Edition.  This was after racing his motorcycle across the county to fend off other buyers as the product came straight off the delivery truck to a Best Buy store!  No one can keep these things in stock.  ...and I tell you, it's a hell of an upgrade.  Over cranking, better lens, better image processing, better UI, and more than just silly old HD!  Don't fool yourself with the Silver or White Editions.  Get the Black Edition. - Fan boy out -


One of the issues with working any new camera into a production work flow is that it doesn't match your existing 'A' camera.  GoPro are still in the infancy stages of providing a tweak-able camera, but it's really work-able if you know what you're doing.  My first call to action was to analyze the color science of this camera to which tone curve on the 5D mark II (and probably mark III as well) match best with the brand new GoPro "Protune" setting.  The goal here is to get the footage to match close enough that post production goes much smoother.  The goal is NOT necessarily how to get the best look out of the Hero 3 - that's an opinion more than anything else.

Let's start with a plot of the tone curves using the excellent DSC color calibration chart.  The gray scale portion of the chart was cropped out of each image and the luma was graphed in Premier Pro.  I chose the "Neutral" picture style because that's the most popular to use with HDSLR video.  The plots below show the tone curve with the picture style contrast set from 0 to -4.  What we see is that the contrast= -3 is the best fit to the GoPro Protune tone curve.  It's not a perfect match, as you can see.  The 5D mark II is crushing the blacks a bit more than the Hero 3.  That's each to fix in post with a little luma curve adjustment.






The next logical investigation is what happens when you turn on Highlight Tone Priority on the Canon DLSR. This, in theory, should give you 1 additional stop in the highlights.  I often use this outdoors in order to maintain highlights, like clouds and light colored buildings, a little better.  Again, the contrast= -3 setting is the closest, but not as close as with Highlight Tone Priority turned off.  The highlights are being rolled off a little better on the 5D mark II, so you're giving up matching in the highlights a little.







Next I'll be looking at the color matching.  That might take a bit of tweaking.  The Hero 3 Black Edition has a "Cam Raw" setting, which is what I'm going to focus on since that seems like the best go-forward solution for outdoor filming with the camera.  Stay tuned for part 2.

Saturday, November 24, 2012

••◊ 2-stop ND grad filter

I added to my arsenal (or scrap heap) of film making gear on Friday.  After what seems like a two month wait my 2-stop ND grad filter came in.  I bought the Tiffen water white 0.6 soft edge horizontal grad filter - if that isn't enough detail for you, then you read too many forums/blogs instead of shooting - you've outed yourself!  It's a very convenient tool that I wish I had many times in the past, especially with these Canon HDSLR's that have all the latitude of a circa 2000 video camera.

Tonight I took my camera up to the top of the hill above my house and decided to try out the filter.  Admittedly this isn't the most scientific of tests nor the best examples but my goal here is to discuss my experience, not do a product review.  Ken Rockwell has much better examples on his web site including the obligatory painted sky sunset examples.

First, let's start with a few examples that did work, in my opinion.  An ND grad filter is generally used to handle an overly bright sky by darkening the upper part of the frame while maintaining the same brightness in the terrain.  The only change I would have made to these examples is the second picture.  I should have rotated the ND filter in the matte box so the ND matched the angle of hillside.  One experiment I still need to do is try a polarizer with the grad ND to see if I can get a sci-fi looking dark sky.





An ND grad isn't a save all.  With some shooting directions closer to the sun all it did was make the sky look polluted.  I would deem these sort of images less acceptable since they didn't give very pretty results - certainly not even close to Ken Rockwell's examples from the link above.  It also seems like as the sky becomes more hazy, due to coastal fog in the last picture below, the effect of the ND perhaps makes the scene look worse.




So an ND grad filter isn't a fix-all for a blown out sky and other exposure problems, but it is a good tool to have in a cinematographer's toolbox.  When applied properly I think it can create some really beautiful results.

Sunday, November 18, 2012

••◊ Spy-clocross at Lake Hodges 2012

Last Sunday I photographed cyclocross racers since our club was promoting the "Spy-clocross" race at Lake Hodges.  The race's primary sponsorship comes from Spy+ sunglasses, so they tweaked the name a bit.  Cyclocross racing bikes are this strange hybrid that Mary Shelley best described; Road frames with mountain bike brakes and tires that fall half way in between.  I thought I was going to post photos that represent the dirty dozen (pun intended), however it ended up being more like the dirty dozen and a third.


The race day started out with the kids conquering the course, sometimes with mom or dad in tow.  The jerseys don't quite fit yet, but neither do the bikes a lot of the time.



Cyclocross races are very different beasts as compared with my experience in road races.  The two "course marshals" at the beach head proved that.  As one was puffing on a cigarette he explained how they recently made one of the other course's obstacles a field of crushed beer cans.  They also took it upon themselves to make the course more difficult by pouring buckets of water into the sand pit shown in the first, second, and sixth pictures below.  One of my friends explained that they often put the beer garden at the finish so the riders can ride right into the beer tent after the race.  I would be searching for the nearest hose to clean off my bike before I packed it away!  As you can see, the course was already hard enough with sand and dirt being kicked up, mud stuck to the bottom of cleats, and relentless hill climbs every lap.  Although there were a couple whiners in the men's 'A' category who didn't want to pre-ride the course for fear of their white skin suits getting dirty.  Can I get a "duh!" here?  







The main instigators of this race were Udo and Kurt.  I lined both of them up at the finish line for their mandatory sponsorship friendly picture.  Udo kept asking me, "did you get lots of pictures with the sponsors' logos?"  Yes Udo, I did. 



What's an outdoors race without wide open vistas?  Yes, there are cyclists in the first picture. You'll need to click on the picture to open it up for a wider view.  With the look of arid desert I figured I should prove that there's actually a lake about a quarter mile away.  The sandy beach where the racers are going through is normally covered in water during the rainy season, as proven by the mine field of dried up clam shells.  This park is normally a boat launch!  Lake Hodges is green about two weeks a year. 



...and finally as the day was drawn down into dusk.  The 'A' category race launch just before dusk, which made the race feel like it was chasing the sun.  These anaerobic events are often lonely races with mostly solo efforts.  The racers are not sure how far behind or how far ahead they are on the course, which makes for a race of nerves as much as strength.  You just have to keep going. 




Saturday, November 10, 2012

••◊ HDSLR sound sync problem

I just found this article about Canon in camera sync audio on ProVideoCoalition.com and thought I would share it.  It turns out that the 5D mark II syncs sound about 2 frames ahead of where it should actually be!  All this time I have been manually syncing audio by perfectly lining up the the waveforms for the production audio and camera audio thinking I was being so careful to get it right.  I should have been slipping the production audio by 2 frames!

Yet another reason I need a real camera.

Saturday, November 3, 2012

••◊ Burning a DVD for film festival submission

Let me first start off by saying that I'm not a big fan of DVDs.  I do, however, have fond memories of buying my first DVD player in 1997 as a graduation present for myself.  I was in Magnolia Hi-Fi in Seattle and they had this new, shiny, slim Panasonic player.  It played DVDs and CD's - remember those days when CD playback mattered?  ...optical out for Dolby Digital in 5.1 surround!  ...S-video, which was an upgrade from the composite video I was used to using on our VCR.  Yes, simpler times.

It's the 21st century now and things have changed for the better.  Shiny disks are sort of obsolete, and for good reason.  We have bandwidth at home.  I get a better quality picture from Vimeo.  However, the South by Southwest (SXSW) film festival still requests film festival submissions by DVD.  It's a bit shocking to me, simply because this gathering has a reputation of being on the leading edge of technology and ecological practices - both of which I appreciate and would be proud to be associated with.  Home brew video DVDs have been nothing short of a horrible, rotten, miserable experience in my time dealing with them.  There's always that one player that doesn't read the disk, or skips around on the video, or spontaneously combusts when you insert the disk because it can't spit it out fast enough - well, maybe not that, but anyone who has burned a DVD at home can sympathize.

So I'm in the middle of burning DVD's for the SXSW festival.  I consulted with my friend and he gave me some advice that actually works, much unlike the black magic voodoo you often find in amateur forums online.

Step 1. Buy good blank media.  My friend said that he uses DVD+R, but I chose to go with DVD-R because that's the most compatible with all DVD video players that exist, even the old ones.  He recommended the USDM brand, so I bought the "Supreme" disks to not take any chances.  I don't have time to experiment with brands and products.  Please note that I am not affiliated with this company, nor the web site I link to in this blog post.  Other brands may work just as well.  This is the brand my friend uses on a consistent basis with success and his business relies on delivering working products to clients.

Step 2.  If you are using Adobe Encore to author your DVD, select "DVD Image" as the output option.  Don't burn the disk directly from Encore.  Don't create the DVD directory.  Create a .iso file of the disk image.



Step 3.  Use a freeware (sponsored) program called ImgBurn to burn the DVD image (i.e. the .iso file) to the DVD-R disk.  Note that you have to scroll down toward the news section to download the correct program.  There are some deceptive advertisements on their web site for DVD burning software.  I mistakenly thought one of these links was the installer and ended up with "Grab-n-Burn" on my desktop.  After removing this junkware from my computer, I found the discreetly placed link to download the actual ImgBurn software.  Heads up. 




When I tested on Sony, Memorex, and generic media I only found one bad disk and it was burned on my laptop.  So far the rest have worked on all players.  I still have to test the disks before sending them out, but at least I have a work-able solution for film festivals now.  I'll repeat this method when my "good" media arrives on Monday.  Hope you have as much luck as I did.