The LightSpace CMS LUT Image
Using the LUT Image for LUT Ripping, LUT based Correction, and LUT Manipulation
The LUT Image within LightSpace is a very powerful tool for direct LUT manipulation, using any graphics program to directly alter the LUT characteristics. With this approach you can easily alter any single point from the 35937 LUT points (the LUT Image is based on 33^3 LUT data).
This is possible because the coloured columns either side of the LUT image contain all 35937 colours within the 3D LUT. Therefore changing any of the colours within these columns will directly alter the LUT data.
LUT Ripping is a very simple workflow and uses the fact that the LUT image can be exported from LightSpace (with a reference image inserted if required) and can then have any external colour correction applied. When the LUT Image is re-imported into LightSpace a LUT will automatically be generated to match the colour changes applied to the LUT Image.
Use 'File/New' to make a new Null LUT, which has no change characteristics (a bypass LUT, where the image data input into the LUT will come out unaltered).
This will automatically generate a new LUT Image, which contains the Null LUT data in the 2 coloured columns.
Next, add a suitable reference image into the Null LUT Image via 'Image/Reference Image/Insert Reference Image', using the pop-up navigation window to select the desired image.
The chosen image can be a standard reference frame, such as Marcy, or a still grabbed from a film or program that represents the desired changes to be made. In this example a desire to lift shadows, without altering the black level, combined with a subtle skin tome adjustment.
The ref image is not a requirement, and has no impact on the LUT, or the manipulations - it is just a guide to help view the changes being made on a real image.
This new LUT Image, with calibration data imbedded, can then be 'Saved' as an image file - either in DPX or TIF format.
Use the pop-up window to select the desired image format, the name the LUT Image is to be saved as, and where to save it. This will save the LUT, with its inserted reference image, ready for external manipulation.
The LUT Image can now be loaded into any external system to have the desired colour manipulations applied, such as grade setting being used within a DI colour correction. With the grade applied the LUT Image can be re-saved, and loaded back into LightSpace where a LUT matching the applied grade changes will be automatically generated.
The above image shows the applied colour correction, and the below is the LUT generated for the correction.
The Ripped LUT can be exported from LightSpace in any desired format and used to apply the same colour corrections via any LUT compatible system, LUT box or display.
LUT based Workflow Correction
LUT based Corrections can be used to pre-correct image workflows where there is an undesirable change occurring to the image, for example when material is converted via a codec that inherently changes the image colour and/or contrast.
The best approach is to add a selection of different reference images to a number of Null LUT Images, so that any compression applied is variable on each frame.
The images should then be processed through the exact same image path, and the individual images averaged together to null compression artefacts. The final single image can then be loaded back into LightSpace where a LUT will be generated matching the changes caused by the image processing. This LUT can then be inverted, and used to pre-correct any images before they are processed through the same image path.
LUT Image Manipulation Workflow
The following example shows how Adobe® Photoshop® can be used to direct alter any component of the LUT, using an imbedded image as a visual guide.
Using the steps described above first generate a Null LUT Image.
Assuming the changes are to be made to a calibration LUT it is now necessary to combine that LUT data to the Null LUT Image. This can be done by simply using the 'Add LUT' function ('Edit / LUT Manipulation / Addition'), or more likely by using existing profile data to build the LUT on-top of the Null LUT Image.
To use an existing profile to build a calibration LUT on-top of the Null LUT use the 'Convert Colour Space' menu, selecting the 'Use Existing / Apply to the Image' option.
This will change the pre-built LUT Image to include the calibration data generated from the selected profile.
Now export the LUT Image, as described above using 'File/Save'.
Then load the LUT Image into your desired graphics manipulation program, such as Photoshop, and alter the image as desired, using the inserted reference image as a visual guide to the effect the changes will have.
With the LUT image loaded in your graphics program of choice you can use any creative tools to directly adjust the LUT data via the LUT Image.
As an example the following show using Photoshop Curves to manipulate just the shadow detail, leaving black alone, and the data above shadows.
A second example shows using Replace Colour in Photoshop to just alter the colours associated with skin tones.
When the manipulated image is exported from the graphics program the changes will be burnt into the LUT Image. The following image split into diagonal stripes shows the original un-modified LUT Image and the new modified LUT Image, showing the way the shadows have been lifted, but maintaining true black as the same black level.
The new LUT Image then needs to be loaded back into LightSpace via 'File/Open'.
When the modified LUT Image is loaded back into LightSpace the changes will automatically generate new LUT data based on the changes.
The following images show the original LUT data, and the new modified LUT data. (This shows just the change in the shadows, as the skin tone change is off the grey scale axis - obviously).
The change in the shadows can be seen easily in the before/after LUT graph.
The new LUT data can then be exported for use in any external LUT box or DI system.
Another use for graphics program based LUT manipulation is to mix between two separate LUTs by using the 'Layer Reveal' capability of such graphics programs.
The concept is to place one LUT Image over another, and reveal through the top LUT Image to the second LUT Image below.
In the following image the top layer is the calibration LUT to be modified buy mixing through to a 'Null LUT Image' on the layer below. This example is using the same Calibration LUT as above.
In this example a ramp image is being used to help manipulate the grey scale in the calibration LUT.
From LightSpace export A Null LUT Image, and a LUT Image combined with the calibration LUT data using the 'Add LUT' function ('Edit / LUT Manipulation / Addition'), or by using existing profile data to build the LUT on-top of the Null LUT Image, as explained above.
Export the Null LUT Image and Calibration LUT Image as DPX or TIF images, and load into Photoshop, with the Null LUT Image as the lower layer, and the Calibration LUT Image as the top layer. The background layer is a bright block colour to show where the 'reveal' is being applied
Using the graphics program tools - 'Select Colour Range' in this case - isolate the areas of the top LUT Image to be replaced with content from the lower LUT Image.
The effect of the selection can be seen using the block colour background by momentarily disabling the lower LUT Image layer, as shown below.
Re-enable the lower LUT Image layer, and save the combined image as a new TIF image file. Import this modified TIF image into LightSpace, where new LUT data will automatically be generated.
The following image shows the new modified LUT data, and when you hover over it the original un-modified LUT data, showing the alteration to the higher-end of the grey scale.
You can easily see the change in the highlights between the before/after LUT graphs.
The new LUT data can then be exported for use in any external LUT box or DI system