Visit to Tulsa

This past weekend saw me taking a trip to Tulsa and taking some photos of the BOK Center in the downtown area.  While I was there I also took a couple of additional photos of the high rise skyline, this time from a different angle.

My HDR brackets ended up having to be hand-held as my tripod became unusable due to an unfortunate turn of events.  Like many tripods, my Giottos is top heavy so can be awkward to carry with its carry-strap.  If given the opportunity it will try to flip up-side-down on my shoulder and when it does this the strap attachment of just looping around the leg bottoms can lose its grip.  Guess what happened?  Yeah, it flipped and the strap popped off the legs causing it to fall head first onto the concrete sidewalk.  To make it worse, it fell onto the mount screw of the ball head, crunching the top of the threads - and as I discovered shortly afterwards, it bent the screw rendering it completely unusable.

So, back to the photos.  I took a mixture of 5 shot and a couple of 9 shot brackets, all hand held.  I was pretty fortunate in that Photoshop was able to align them and remove ghosts with minimal effort on my part when I merged them to HDR.  I also tested them out in trial copies of Photomatix and HDR Expose with varying success - of the three HDR merges, only two packages were able to align the images and remove all the ghosts automatically.  HDR Expose has some nice features but it requires a lot more work up-front to get everything aligned and ghost free, not helped by what appears to be a trickier to use manual toolset.

Before I get to posting the photos, I wanted to briefly touch on my last couple of posts about creating and using a linear camera response curve and how my first attempts weren't that successful.  I'm still finding that having Lightroom use the Camera Neutral response curve gives me the most consistent results and none to minimal banding and posterization when processing and merging the bracket images.  I also made a very interesting discovery about my Nikon D2X.  I downloaded a trial version of Nikon Camera Control and connected my camera so I could check the response curves installed and in use.  What I found is that it is using a completely flat, linear response curve.  I can't say if this is the factory setting from Nikon but I can say that it is what it is currently using.

Okay, enough talk, it's time to get some photos posted here.  So here are a selection of tone mapped LDR versions of the HDR's I took of the BOK Center:

And finally, here's my tone mapped image of the Tulsa skyline taken from near the BOK Center, to give a different view to the "usual" Tulsa skyline photo:

Curve ball

After writing my last post I continued to test out the linear curve profile on other HDR images, including several multi-exposure ones.  And the more I tested, the more I found inconsistencies were creeping in.  I started seeing banding, posterization and increased noise appearing in the HDR files.  It seems that while the theory is pretty sound, the practice needs further investigation.

Something about the profile creation went wrong - but not completely, as a couple of HDR images worked really well with the profile.  So, until I can figure this issue out I will be utilizing the "camera neutral" profile within Adobe Lightroom as it is the most linear in behavior.

Throwing a (linear) curve

While doing further reading and research on the technical aspects of HDR Imaging I came across a pretty large issue concerning image curves.  Namely how Adobe Lightroom does not apply a neutral linear curve to your images.  Now when you are only working with single images, this is not necessarily a bad thing however, when working with multiple images for HDR's (3, 5 or even 9) this can become a big problem as the colors don't match up from image to image.  

Enter the theoretical linear curve, one that is completely flat from light to dark; which when all the images are stacked and merged keep all values of light, dark and color channels in their correct relationship to each other.

The problem is neither Lightroom or Photoshop has this linear curve profile and even using something like the "camera neutral" profile in Lightroom, there is still a slight curve to the profile which throws in mismatches.  How to modify these profiles or create a new one to fit my needs?

Which brings me to when (yesterday) I was browsing the forums on www.hdrlabs.com and found the answer.  Adobe provides the tool to create a custom profile in their DNG Profile Editor.  With it, you can create a custom camera profile that is completely linear and then export it into Lightroom (if like me you use Lightroom as your main workflow tool) and in turn apply to each of your images prior to exporting them to your HDR creation program of choice.

So, now you may be asking yourself, how do I create a custom profile - well here it is in a nutshell:

1. Create a DNG of one of your photographs.  Again, Adobe has a free tool to do just this which is either standalone or included in Lightroom - Adobe DNG Convertor
2. Open this DNG file in DNG Profile Editor and in the window that comes up ensure all the adjustments are zero'd and then on the Tone Curve tab, select Linear for the Base Tone Curve.  You want this graph to have the line completely straight from bottom left to top right.
3. Save the Recipe - name it something useful to you
4. Export the Profile - this will then add it to Lightroom for you, and can be found in the Develop Module under Camera Calibration
   
5. In Lightroom, select the exposure stack, select this new profile and hit the Synchronize button to apply it to all the images in the selected stack.  This is also a good way to insure all develop settings match across the stack prior to creating the HDR Image

You are now the owner of a fully custom camera profile that has a truly linear response curve.  I now have one for my Nikon D2x, which is my current main camera.  It will be a good idea to go back and create on for my Nikon D100 too in case I want to get creative with photographs shot on it, as the profile created in DNG Profile Editor is camera specific, being that it is built off of the curve response of the camera the DNG file was taken on.

After all this you may be thinking "Is this all really worth the effort?", "Will a linear curve really improve my HDR Images?".  In my brief experiments since creating my custom curve I can give you a simple answer to those questions - YES!

Deep diving into HDR

Despite my lack of updates here and/or photos being posted I have been pretty busy and doing research and testing of HDR processing techniques.  And it has been pretty illuminating for me.  I've also learned that there is a lot more to making good HDR Images than just taking a sequence of photos and slapping them into something like Photomatix (good software, trying out the trial version).  While this may produce a HDR image, it will likely be very far from it's full potential.  One of my biggest finds is that despite my not having set any "default processing" of my NEF RAW files on import to Adobe Lightroom, they were being modified and altered slightly, so they were more likely to suffer highlight and shadow clipping when processed as HDR's.  This led me to start looking more closely at RAW convertor software and also what (if anything) could be done to minimize Lightroom's interference on RAW files.

My research led to a wonderful free (donations will unlock additional features) software package called Raw Photo Processor - caveat is that it is Mac only, which is not an issue for me.  Now this convertor keeps the RAW files as neutral as possible, so much so that they look very "cool" in comparison to other converted RAW files from other convertors.  I almost feel that they need a slight warm tone added to mimic what I see with my eyes.

I also found a minor modification to make to Lightroom to correct the unexpected and unwanted modification to my files on importing.  Under the Camera Calibration section of the Develop Module, change the profile to "Camera Neutral" to minimize any automatic processing and/or changes from what your camera captured.

As I move forward, I will most likely move away from using Lightroom and Photoshop as my primary software for creating HDR images.  Photomatix, while not perfect, is the most popular program for producing HDR images and tonemapping them and my testing/trials of it have confirmed that I will be getting a full version.  Now Lightroom is my primary cataloging and processing software so it will be staying as part of my workflow, especially now I've minimized it's interference with my RAW files.  I will likely keep using it to feed RAW's to Photomatix, although I'm seriously thinking of making a donation to RPP to unlock all the features and continuing to evaluate it against Lightroom to get the most neutral files to produce HDR's from.

I'll also continue reading the HDRI Handbook 2.0 from the people over at HDRLabs.  If you are really interested in learning about the technical aspect of creating HDR images, it is a very good read.  The website is also a very good resource that I recommend checking out.

As a visual representation of how my technique is evolving, I thought it would be interesting to post some comparison samples of one of my images so you can see how much things have changed.

From left to right you can see the progression from my original HDR image, through to my latest version (still using Lightroom and Photoshop to merge and tonemap).  Certainly some significant improvement in the overall look.