Transition Points

Transition points are points in the brightness scale where we move from a normal image zone into an inverted zone – and of course where we move out of an inverted image area into a normal one. With complex manipulations you may have inversions adjacent to each other, without a region of normal gradient.

Often the most interesting effects come from setting a transition point in the middle of the tonal range of an object, especially when the object is a reflective surface like chrome or polished paint.

The following transform shows the tonal range of the oil tank between the outer red lines, with the middle line showing a point on the curve of the tank that I selected as a starting point for experimentation. This formed the experimentation range for my first example and as you experiment you will see that moving the transition point between the red lines produces some interesting effects on the oil tank as well as the image as a whole.

Compare this image with the predecessor. There is already quite a change in the effect, although there has only been a relatively small change in the transition point.

Some other points to note

• The filler on the oil tank has become outlined and almost moved to a line art representation
• The highlights on the forks have become a striking dark stripe
• The lights have gone dark, but not turn signal lights which are brighter as these are below the transition point
• The lightening of the sky has reduced the intrusion of the vapour trails. Lightening the sky and compressing its tonal range can remove a lot of unpleasant effects, although it also tends to remove interesting things like clouds.
• Grass and trees are lighter, those on the right (mostly cropped in my illustration) have developed a halo which resembles leaves, yet the trees were bare) and one tree has gone white. This halo can work well for us, not only here, but as an outline for objects within the image.