I have been reading the ACR and Lightroom Profile SDK and tried producing a profile that would invert an image using a Look Table. It seemed to me to be quite simple, but it didn't work.
My logic was that the HSV look table should be easy to produce inverted colour: if the hue <= 180 then add 180, otherwise subtract 180. Leave the saturation and value unchanged. I decided the look table only needed two entries, so my csv file contained:
2, 1, 1, 0
180, 1, 1
-180, 1, 1
This didn't seem to do anything. Reading a bit more from the dng spec 1.4.0.0 suggested that each hue value should have at least two saturation values, so I changed the csv file to:
2, 2, 1, 0
180, 1, 1
180, 1, 1
-180, 1, 1
-180, 1, 1
This at least made a visual change to the image when applied as a profile, but nothing like a negative of the image. Adding another hue division:
3, 2, 1, 0
180, 1, 1
180, 1, 1
180, 1, 1
-180, 1, 1
-180, 1, 1
-180, 1, 1
changed the image a bit more. Then trying four hue divisions changes the image again, but adding more hue and/or saturation divisions resulted in no further changes to the image's appearance when applied as a profile. I created another profile with a reversed point curve to visualise what I was actually trying to achieve.
These are the preset previews for profiles I created using ACR (Invert LT21 - Look Table 2 hues, 1 saturation, Invert LT22 - Look Table 2 hues, 2 saturations, etc) All have a single value division. The last one, Invert PC is the point curve inversion (a proper negative).

Anyone got any clues as to where I'm going wrong in my thinking or have I totally missed the mark somewhere?
My logic was that the HSV look table should be easy to produce inverted colour: if the hue <= 180 then add 180, otherwise subtract 180. Leave the saturation and value unchanged. I decided the look table only needed two entries, so my csv file contained:
2, 1, 1, 0
180, 1, 1
-180, 1, 1
This didn't seem to do anything. Reading a bit more from the dng spec 1.4.0.0 suggested that each hue value should have at least two saturation values, so I changed the csv file to:
2, 2, 1, 0
180, 1, 1
180, 1, 1
-180, 1, 1
-180, 1, 1
This at least made a visual change to the image when applied as a profile, but nothing like a negative of the image. Adding another hue division:
3, 2, 1, 0
180, 1, 1
180, 1, 1
180, 1, 1
-180, 1, 1
-180, 1, 1
-180, 1, 1
changed the image a bit more. Then trying four hue divisions changes the image again, but adding more hue and/or saturation divisions resulted in no further changes to the image's appearance when applied as a profile. I created another profile with a reversed point curve to visualise what I was actually trying to achieve.
These are the preset previews for profiles I created using ACR (Invert LT21 - Look Table 2 hues, 1 saturation, Invert LT22 - Look Table 2 hues, 2 saturations, etc) All have a single value division. The last one, Invert PC is the point curve inversion (a proper negative).

Anyone got any clues as to where I'm going wrong in my thinking or have I totally missed the mark somewhere?
Anthony Blackett
Cameron Rad
john beardsworth
Cameron Rad
john beardsworth
Victoria Bampton - Lightroom Queen, Champion