We Three Curves of A-C-R

11 November 2009

I was asked a question through Model Mayhem recently about curves settings in Lightroom as well as the impact of a linear vs. logarithmic conversion process. That got me playing with the conversion engine a bit more experimentally than normal and made some interesting observations. Most of these won't be new to the true photo geeks out there, but as they were to me... well, it was something to write about on a rainy Veteran's Day (btw, Happy VD guys).

So what am I talking about? Well, it's important to start by understanding the logarithmic nature of how we perceive light and dark vs. the linear way in which digital imaging captures it. Rather than rehash what's already been better written, I refer you to Bruce Fraser's excellent article over at Adobe on the subject. The gamma curve which he refers to is applied by the ACR engine as part of the camera profile, and looks like the image below in its default form. For the purposes of our discussion, this will be the Tone Curve. The next two curves in the processing chain are applied almost simultaneously, those being the Parametric and Point curves. It's important to realize that they act independent of one another, as well that while Lightroom and ACR are very much the same engine, they do not behave the same way here. In ACR, one can utilize the Point Curve just like a Curves adjustment layer in Photoshop, whereas in LR we are limited to the selections "Medium Contrast", "Strong Contrast", and "Linear." Indeed, sometimes ACR is better for conversion than LR. In any case, this affords you three levels of control over how your image ends up being presented to the user, and three opportunities to maximally extract quality detail over the image range.

The next question many folks will have is how to utilize that first Tone Curve to suit your purposes. This requires use of Adobe's DNG Profiles Editor. I will be honest with you that it's a bit cumbersome to work with, and requires opening of an image which has been converted to DNG in order to create a camera profile for that model of camera having the Tone Curve you desire. Details of its operation can be had from the Adobe page linked above, but if you have questions, please feel free to ask.

The photo at the top of this has almost nothing to do with linear vs. logarithmic conversion, but I thought was a nice demonstration of careful post work by Sarah. Milanya is a fantastic model, btw, and if you're in the DC / MD / VA area you should book her ASAP.

Social Networking & Photography

23 June 2009

Just a quick note for those who take pictures and use Facebook, MySpace, etc. In an attempt to retrieve some of my sanity, I've rejoined a bit of the social world only to find that if I try to share my photos on these sites they end up looking like utter crap. Now, saving space and bandwidth is a laudable goal of course, but destroying the appearance of something one has put some time into is another thing. So, what do you do?

For MySpace, save your images as PNG. For some reason their backend doesn't allow itself to transcode photos, and so once you upload a PNG, it will keep it as a PNG. Keep your image within their sizing requirements (600px I believe) and it won't resize them either. As a note, if you edit in 16bit, do be sure to switch to 8bit before saving, as you'll be wasting a lot of space and slowing viewers' downloads otherwise.

Facebook is another story. It will transcode every image uploaded into JPEG, and insists on recompressing your image regardless of its original size. Your best bet is to maximize JPEG size / quality on the original save to preserve as much detail as you can when it recompresses. Again, you're stuck at ~600px for your maximum dimension.

See a comparison of FB transcoding and recompression here: http://www.facebook.com/album.php?aid=2025397&id=1484857429&l=ecff6205e4.

Update (11/2/10): FB now allows images up to 720px on the long axis. A huge 'thanks' to Ofir Abe for letting me know! I should probably spend more time on FB, huh? :)


09 March 2009

Wow. 6 months without an update. I'm starting to remind myself of my brother updating this infrequently. Or maybe it's my my wife. Either way, it's been a while. Nevertheless, this past weekend was exceptional from the standpoint that Sarah and I were able to - on top of spending the entire weekend together - visit the Eastern State Penitentiary in Philadelphia, PA. Some folk say it's haunted, and a few folks claimed to have 'seen' something (to include a certain someone whom I room with...), but I call BS. Still, it was a lot of fun and resulted in some cool pictures like what you see to the left. The version you see is the post-PS version, but I'm kinda proud that the majority of the image came about in-camera. You can see the ~SOOC (Straight Out Of Camera) shot here.

Was that enough links for one post? How about one more?