Small areas with high calculation costs aren't distributed into enough threads

Hello,

this one might be a low priority one, but it's something I noticed and thought I should let you know. From what I can tell, UF uses image pixel column count to separate the image into pieces that are being worked on by each thread. This works fine in almost all cases, but I encountered something interesting. If only a small area is left for calculation, and it is comparatively narrow, UF won't spawn additional threads to work on it. I suspect it's set to spawn a new thread only per minimum amount of columns left to calculate.

As you can see in this screenshot, the fractal isn't finished, but UF only uses 5.5% of my CPU. Notice the narrow pixelated column:

Best regards
Phillip

//edit2: UF 6.03 + Windows 10
//edit: in case anyone wants to test this:

Fractal2 {
::vogXfjn2NJ1yuuJMQ09Ix/gF7DX/Ajhbl3Up21V629RuGDYFjNy2p3k/3+h0BINNgECPn5Mz
  ZOeGjKdW5evsAhy2szIr++RIaF6T7QeWS5tY0sxONnlkmGMypubiJJZjjOaGs5ks6HzWnzu+
  l236fjipkqyi982rsWtmtBvs6rK9lpY4qfoCFWVab+ukgxoFTeOMIXu6y2VVKVWsoWXt+pD6
  Gf2Elnw1cRHm10RYCODefDC1ywtCCprpvjIEoF1kX201yrp8+2N2K/EMWnoNkacLtDlyRTWP
  Lx19NYGKdx8p8ErmjJ0yixQEEhavtLqb2t+yxHPoVTUPb0XkhxR0o1Z8qFww+pJlnMu/4HM1
  XHXq24CKOeXWlBIYKObupWWdmK065fpsuw182YfU0zgVCfzbCqvH+7C0YJhA+r1nsDmjLnoy
  nGB14DeTZBUhnQDGINwIx1YcPrlJ+fyOr3oivo1PyK/gKOUfV7eVof72KUXf2qcfsEC5ZQ1b
  qdw+bTcyIvbSwJdw/84G5n4JtC8YwgLLmiqBLUpdpl2r1O7YIr2XC4tILYVbjYPSHchokwYM
  ClRfAQps9r9DsWhQQ6FPwg8eA0wEC+/i239IKf7W8xq1rSwHekK+5iHlzLL+LUvhvXB=
}

Testgelände.ufm:testing_example {
::I1y4Rin2NGVwONMMM07Vq/DWlLbFxULDOAihq4DhJv10hpppRNpQb1+4JeJUY7Aib+9e+9sj
  DpI7jxRAMBbgr00gQyohzQjnhqdos4IZbre250r3CXfhDcnZx4yLEYz1OmcGQVu6n3AF1N4A
  T4H8kvkztwmO56eR+NF2lpjeBO8CT6YQwsMNYOsZAIUlUVc0Okkt9+33xpjwTQRgKOqUUh9S
  vmlsShzbiWijk6Agdt9qyEWrBPo4YXdvHNQWRnjI/uHYCN2hNwcq8WsH1WqlNl8inH+Al9iE
  vcYwcEZZry8kNE3feY3PFKXXJbRbYGmLtnta96/yg9/YgUf3+P/B/aDPvdznkd/b+T2o+0Fz
  KMW3FbrYAb0Sx237lEe6laEiSXHz/8hbkja+a9Fiutqi
}

I get similar results. UF 6.03 on my Windows 10 computer uses 12 threads. Task Manager showed UF using about 97% of CPU for the first 0:40, then about 21% for the next 1:20, then about 11% for the remaining 2:30.

UF starts by splitting the image vertically into as many areas as are needed to keep the available cores running. When one of these strips is finished, the remaining strips are subdivided to keep all cores busy. However, to keep the Guessing drawing method working optimally, the minimum strip size is 16 pixels and this is what you're seeing in the example.

Oh, always interesting to get a peek under the hood, so to speak.
Thanks for the response