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UFRAW Tutorial

LPROF is an open source application that creates ICC profile for cameras, scanners and monitors.

Photographing the IT8.7 Target

Capturing the target correctly is critical to producing a good profile and is perhaps as large of a factor as 80% to 90% in determining how good your profile will be. First I will talk about how to create a general purpose camera profile. That is a profile that can be used for most images where the light has a smooth spectrum (direct and shaded sun light, cloudy, flash and tungsten light but not florescent light) and the white balance of the actual scene is close to what was set on the camera or selected/set in UFRAW. 

Here are some tips for getting a good IT8.7/2 image:

Process the Target Through UFRAW

Open the raw file in UFRAW. Set all of the controls to the default settings as a starting point. White balance should be correctly set for the type of lighting you used when photographing the target. Direct sunlight, cloudy, shade or incandescent are all good. Do not use fluorescent lighting. There are way too many variables to get results suitable for general purpose usage.  Start out with gamma set to 0.45 and linearity set to 0.10.

In the corrections tab set exposure to 0.00 and saturation to 1.00.  Do not use Black point compensation or a camera curve.  All of these are the default settings.


Then click in the patch in the lower left corner (the lightest gray patch) to display the spot RGB values and increase/decrease exposure until the spot value readings are between 210 and 230. But make sure that no readings anywhere on the target are above 245 to 250. The patches at A13-19 can be brighter than the lightest gray patch so check these very carefully for any spot values that may be over 245 to 250. This controls how bright your images will be when using the profile created using this target. If your images are too bright then make the target brighter and vis versa. But these setting should get you in the ball park.   Also remember that is it critical that no spot values anywhere on the target are 255 so this limits how much exposure compensation you can use to darken your images with the profile.

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Now click on the DMAX patch (lowest patch on the right) and check it's spot values.  This should have RGB values between 10 and 20 and it's spot values should be clearly different from the patch(s) next to it.  If the spot values of the DMAX patch are close to zero then decrease the setting of the linearity slider.  If the DMAX patch has spot values much higher than 20 increase the setting of the linearity slider.  Go easy this should be some where between 0.05 and 0.15 in most cases.  If the spot values of the DMAX patch and the patch(s) next to it are not different then either your camera does not have enough dynamic range to capture these darker colors or the image was under exposed.

You can also check how even your lighting was by checking the spot values around the gray borders of the target image.  These should not vary much as you check different locations on the image.

Set both the Input Profile and the Output Profile to sRGB and Intent to Absolute colormetric.  This will prevent UFRAW from doing any color transformations in the process of creating the image from the raw photograph of the target.  This is exactly what you want for processing a target image to be used for creating profiles.

Now click the Save As button to save the target image as a 16 bit TIFF file.  Do not save it as a JPEG image as this will result in poor quality profiles.

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Create the Profile

Now you have the target image that will be processed by LPROF to make a profile for your camera.  Please see Camera and Scanner Profiler Tab for details on how to create the profile.

Using the Profile

To use this profile in UFRAW you will need to open a RAW file and select this new profile as the input profile. UFRAW will initially set gamma to 1.0 and linearity to 0. Reset these to 0.45 and 0.10 (or to exactly what you used when converting the raw image of the target) and adjust exposure to 0.0. For your output profile select a working space profile such as AdobeRGB or even better a profile with a larger gamut such as BetaRGB, PhotoGamutRGB or ProPhotoRGB. Stay away from sRGB as this has way too small of a color space to preserve all of the gamut that most digital cameras can capture. Set white balance to Camera (assumes you set the correct white balance when shooting the image) or select the correct white balance setting for the lighting you used to shoot the image.

Making Profiles for Specific Lighting Conditions

Making color profiles for specific lighting conditions is a variation of the above. The hardest cases and the ones with the biggest payoff involve florescent lighting. There are a number of problems that you must deal with to get good profiles for this type of light.  
First different lights can vary significantly in color temperature. In fact the color temperatures for florescent lights range from around 2700K (very  common) to around 9300K (not common). Therefore the florescent white balance setting(s) on most cameras are all but useless. Secondly florescent lights that are not high CRI (Color Reproduction Index) lights (almost all of them) will have very large spikes in the color spectrum. Where these spikes are located and how large they are varies depending on the manufacturer, the model of the light and possibly other factors such as age and room temperature. 
My experience is that I need to go through a 2 stage process when shooting the target. First create a custom white balance setting before shooting the target so that the white balance that was used in the right ball park and also so that this white balance information is part of the data in the raw image file. For this I carry and use a gray card.  See the documentation for your camera for details on setting it's white balance. Then shoot the target being careful to get even lighting. When running the target through the raw converter be very careful to make sure that you use the same white balance setting as the target was shot with ie. the custom white balance I set at the shoot. And of course everything else above about how to raw convert the target and how to create and use the profile applies. 
This should also work with other lighting conditions where the camera white balance presets are not correct and/or where the light has strange characteristics like spikes or drop outs in the spectrum.

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