Quote Originally Posted by Johnny Rasmussen
Interesting. I am beginning to think thatyou are seeing the true capability of the 14-bit sensor. Do you have some images from your own camera shot with HTP on? That should move both vertical bars 1EV to the right and give you -10EV (theoretical shadow DR) to +4.5EV.

I don't usually shoot with HTP, since the highlight preservation comes at the expense of increased shadow noise and the 7D doesn't really need any 'help' in that department. But, I just grabbed a couple of test shots -/+ HTP - the desk lamp against the closed curtain was intended to result in a histogram with peaks at both ends of the DR. The one on the left is without HTP, the one on the right is with HTP.


[img]/cfs-file.ashx/__key/CommunityServer.Components.UserFiles/00.00.00.35.15/7D-RAW-_2D00_HTP-histogram.jpg[/img] [img]/cfs-file.ashx/__key/CommunityServer.Components.UserFiles/00.00.00.35.15/7D-RAW-_2B00_HTP-histogram.jpg[/img]


As you can see, the DR 'window' does shift 1 EV to the right with HTP, compressing the shadow end and giving some additional headroom on the highlight end. It's worth noting that in the non-HTP image of this contrived scene, there are pixels in the RAW data that span the full dynamic range represented in the DPP histogram.


As an interesting side note, parts of this simple image can be easily resolved on the histograms - the peak at the far right is the bulb, and the next one just to the left is the lamp shade. The big mushy peak on the left is the curtains. It's interesting that there is a series of peaks in between (-3 to -1 EV), seen only on the +HTP histogram. They might represent the forward folds of the curtains that are brighter than the backward folds, and get progressively less intense further from the light - but it's certainly not an obvious visual difference between the images, so it's interesting that HTP resolves them. I wonder what that says about the algorithm. But then again, those peaks may be an artifact of the processing, which is probably intended for 'real world' scenes and is here being applied to something pretty artificial. Some noise reduction algorithms can actually create patterns in a blank region of an image. One of those peaks is at -1 EV, and there's nothing in the image that stands out to me as a patch of something one stop darker than middle gray - that sort of supports the artifact idea, but really, I have no idea what's going on there.


Regardless, in any case, HTP does appear to offset the DR to the right for me.


Quote Originally Posted by Johnny Rasmussen
I still don´t understand the differences between the rendering of the histograms. Think I have to ask Chuck Westfall about that.

Great idea! If you ask him and he responds, please let me know what he has to say.


Thanks again!


--John