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Creating Raw Tone Curves
- Download the gmccrtc.rb Ruby script if you don't already have it. Be sure it's executable (Linux and Mac). You'll need to have a Ruby interpreter, so you might need to download and install one of those, too.
- Download test images from Imaging Resource. From the review page, click the "Samples" tab. Beneath the line of tabs, on the left, select "Thumbnails" if it isn't already selected. Scroll down -- probably to the bottom of the page -- to the viewfinder test samples. They look a bit like a TV test pattern, with a GretagMacbeth ColorChecker just to the left of center. If they don't provide that, scroll up to find some other images with the GM ColorChecker (usually their Dave Box). Starting at the top of the group of thumbnails, look for the first one that has a Raw-file link and which has a "native" ISO for the camera. Click the link to bring up the download page, then click the link on that page to download the Raw file.
- Start up LightZone, navigate to where you stored the Raw file, and open the Raw file. Open the lightzone.log file and take notice of the precise file name that LightZone was looking for.
- If the camera in question uses the same sensor and processing chip -- or maybe even just the same sensor -- as another model that already has a Raw Tone Curve, copy the existing RTC into your LightZone/Templates folder and rename it CameraDefault;[RTC_file_name]. That template should magically appear in LightZone's Styles panel, under CameraDefault; you don't need to restart LightZone. Try it out. If it looks good, you're done! Otherwise, delete it from your tool stack and proceed on to the following steps.
- Add a B&W tool.
- Add a Blur tool, and set the radius to somewhere around 10-15.
- Select the Sampler tab in the top-right.
- Start a command-line window and change directory to the folder containing the gmccrtc.rb Ruby script.
- Start entering a command line that will run gmccrtc.rb, but don't hit enter.
- Pass your cursor over the 24 ColorChecker boxes one at a time, left-to-right, top-to-bottom, and enter the Luminosity values (top right of the Sampler box) onto the gmccrtc.rb command line. Finish off the line with a > [your_LZ_template_folder]/CameraDefault;[RTC_file_name].lzt. On Windows you'll probably need to use back-slashes instead of forward slashes and enclose the whole path in quote marks. On Linux and Mac, you'll probably need to escape the semi-colon and all spaces with back-slashes.
- Hit enter to run the script. If all goes well, a new entry will appear in LightZone's Styles, under the CameraDefault section, for the camera. If the CameraDefault section goes away entirely, that means that the new file contains garbage -- usually an error message -- so look in the file and then delete it. If nothing happens, the file name probably wasn't right -- check the Templates folder to see what name got generated, and correct the command line appropriately.
- Add the new CameraDefault to your processing stack, and drag it below the Blur and B&W tools but above the Raw Adjustment tool.
- Make a quick re-check of the luminosity values of the bottom row of the GM ColorChecker. Desired values are 232, 149, 91, 49, 23, 8. The first box will usually fall well below 232, but it should be above 200. The others just need to be somewhat close.
- Click the lock symbol at the right end of the CameraDefault tool's header and unlock it. Then click the triangle on the left end of its header to open it up. If necessary, double-click the name and change it to "RAW Tone Curve".
- There are adjustment lines for all 15 intermediate half-zone levels. These can usually be simplified down to somewhere between three and six.
- Usually the bottom five or six lines can be deleted, being off-scale for black. Watch the Luminosity readout for the bottom-right (black) box on the GM ColorChecker while you try making some noticeable adjustments to the lines, starting from the bottom. When you find the lowest line that has any effect, use Ctrl-R to put that line back. Then delete all of the lines below it. Adjust that line to try to get that black box to have a luminosity somewhere around 8.
- Similarly for the bright end, trying to get the "white" box at the bottom-left of the GM ColorChecker somewhere close to 232. You probably won't be able to get it that high. Also, some of the upper lines will overlap, making it more difficult to select them.
- Look for lines that are fairly evenly spaced between their neighbors. Click the "x" button on the line and see if it makes any real difference in the image.
- Tweak the remaining lines to try to get that bottom row of the GM ColorChecker somewhere close to the target values of 232, 149, 91, 49, 23, 8. You may need to add adjustment lines back in, and maybe delete one you'd kept. It's an art, not a science.
- When you're happy, close the tool up with the triangle on the left end of the tool's header, then right-click the header and lock the tool.
- In the LightZone menu, click "File" and "Save As Style..." Put the required file name (from the lightzone.log file) into the Name field, and CameraDefault into the Folder field. Turn on the RAW Tone Curve checkbox and turn off the checkboxes on the other tools. Then click Save.
- Open the saved style file in a text editor.
- Round the values off to five digits.
- Replace the version-8 header with a version-6 header from another Raw Tone Curve file.
- Save the style file, then verify that it still works in LightZone.
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