Digital Light & Color

When trying to build a lookup table with a reference image i got "Reference image has wrong dimensions" message even when the reference image has exactly the same dimensions as the image that needs to be processed. What is the requirements to the size of reference image?

To create a lookup table you need to start with a reference image generated by the Transformation/Test Patterns/RGB Cube command. You then apply the set of transformations to this image that you want the lookup table to apply to other images. The transformations need to leave the dimensions of the image the same and not do any blurring or sharpening, cloning or anything else that destroys the integrity of the RGB cube image. Finally, using the Color Lookup transformation you specify the modified RGB Cube image as the reference image. If you want, you can then save the lookup table as a cube file. The RGB cube image contains small patches of colors in the RGB color space in a grid than covers the entire color space. This is what makes it possible to create the lookup table.

A typical way you would do all of this is to start with some typical image you want to apply an effect to and then add as many transformations as necessary to get this image to look the way you want it to. The goal is to create a lookup table or cube file that applies this same effect to other images. To do this, first use the RGB Cube command to create a new reference image. Next, copy all the transformations you applied to your starting image to just after the RGB Cube image. Finally use Color Lookup to create the lookup table from the modified cube image.

If I have a bunch of images, but with uneven exposure or WB, and I would like to make them look similar, is there a preliminary step to standardise the lighting before applying the recipe above?

You could try Autorange for exposure and Color Balance with auto white balance for white balance.