Also, I'm not familiar with C1 (although I'm going to have to get familiar with it, since the plusses don't open in anything else). Can a custom curve be applied within C1? Also, does Phase One provide any alternate curves to their default that I could try, or am I going to have to create my own?
[{POST_SNAPBACK}][/a]
It's been a while since I've used C1, but I believe you can put your own custom curves into it. Besides, Edmund says you can, and he does seem to know his way around the low-level details of image processing, so I believe!
It's going to take me a little time to digest the DNG portion of it.
[a href=\"index.php?act=findpost&pid=135556\"][{POST_SNAPBACK}][/a]
The weird dng conversion step happens because the tool (dng_validate) is designed to check the validity of DNG files being written by third parties (C1 4.0, DxO optics, etc...) The conversion to DNG shouldn't affect your measurements at all. Let me run through it step by step.
1) Process the file to be examined with Adobe's [a href=\"http://www.adobe.com/products/dng/]DNG Converter[/url] tool. Be sure "preserve raw image" is checked under preferences to ensure that our raw data isn't processed during the conversion step. (That would mess up the readings you'll do later.)
2) Download the
dng_validate tool. It's a part of Adobe's
DNG SDK. (Once you unzip the package, you'll find dng_validate under dng_sdk_1_1/dng_sdk/targets/mac/release/dng_validate (or ...win/release/dng_validate.exe).
3) Run
dng_validate from Terminal/the command line as follows on the DNG file you created in step one. Using the following command will give you both the pre- and post-gamma-corrected image:
dng_validate -cs3 -3 stage3.tif -tif stage4.tif <name_of_file_you_made_in_stage_1.dng>Stage3.png (downsized and saved as png for web with no JPEG artifacts)
[attachment=3084:attachment]
Note the strong green cast of the stage3 file. This is because it was outputted before white balancing was performed. Also, gamma correction, color space conversion, noise reduction, and so on have not occurred yet either. This way you're getting a good look at the actual sensor data. My white square on this image averages to around 135 (on a 255 scale). Here's a look at the very same image post-gamma corrected:
Stage4.png (downsized and saved as png for web with no JPEG artifacts)
[attachment=3085:attachment]
This white square measures about 235/255--very near the top of its useful range. Apply a different curve, and you can control how much this highlight is boosted.
Here is an example where I used my own curve to create more headroom. This was pretty quick and dirty, so note the extra contrast, density in the shadows, etc. These will be the tradeoffs for more headroom, and you can design your curve to balance all of these aspects to your taste.
[attachment=3086:attachment]
Note that the white square measures around 200/255 in this image.
I do understand that I can use a custom curve to give me more highlight headroom at the expense of the shadows, however I've never done anything like that. Do you have any suggestions on where I might read up on how to do that?
[a href=\"index.php?act=findpost&pid=135556\"][{POST_SNAPBACK}][/a]
How about right here?
(As you mentioned, now that you're on your + back, you probably can't use ACR for raw development until the next rev unless you're tethered, but for the purposes of your testing, you can use your P45 files to build the curve you would like.)
Using ACR (screenshots below are from ACR4.1), go to the Tone Curve tab (second tab from the left under the histogram display at the right of the screen) and click the Point tone curve sub-tab.
[attachment=3087:attachment]
Now ACR will let you create the curve you'd like and will apply your curve to the curve being used to apply gamma to the sensor's linear data. Or, in plain English, you can use your curve to get more headroom.
Here I used the TAB key to move between the points on the medium contrast curve, and droped them all about 25 ticks (press the down arrow when you're on a given control point). I generally don't use the mouse when manipulating these control points if I need to be precise.
[attachment=3089:attachment]
Using the little doohikey at the top right of the panel, you can save your curves, make them default, load others, etc. to your hearts content. In the end, you can customize this to your curve automatically whenever you're bringing in new files, so your workflow goes right back to normal, but now your back is giving you however many stops of headroom you require.
[attachment=3088:attachment]
The bottom line is to remember that the results you're seeing aren't the hardware, but rather the culmination of some set of tradeoffs someone at your raw converter's company made. The nice thing about many of these raw converters is that they let you override those tradeoffs for your own preferred set of tradeoffs.
Hope that clarifies it for you. Enjoy your back!
P.S. It's a shame we will have to wait until at least ACR 4.2 to get proper + support for our backs. I will be in precisely the same boat once my + back arrives. I will look at trying to figure out why tethered + files work in ACR 4.1 and unthethered ones seem not to. Perhaps I can patch the untethered files to look like tethered ones, so that the will work in ACR 4.1. If you wouldn't mind sending me a P45+ untethered raw file I'll take a look and see if this is feasible. (My e-mail can handle large attachements.)
Best regards,
Brad