CONTROL — the eff glow's fade-in must be linear at a constant step
  alphas [34, 68, 102, 136, 170, 204, 238]  steps [34, 34, 34, 34, 34, 34]
  => 2.000 units/frame; t(f) = 2*f - 171
  check: declared hold ends t=45 -> predicted frame 108.0; observed last full-alpha frame 107

LOGO — palogo_gamearts, checked against that calibration
  observed: first drawn frame 116 at alpha 255; full alpha through 198; fade-out 199..211
  declared a=  0 at t= 15 -> frame   93.0   observed alpha NOT DRAWN
  declared a=  0 at t= 30 -> frame  100.5   observed alpha NOT DRAWN
  declared a=255 at t=190 -> frame  180.5   observed alpha 255
  declared a=255 at t=194 -> frame  182.5   observed alpha 255
  declared a=232 at t=206 -> frame  188.5   observed alpha 255
  declared a= 32 at t=210 -> frame  190.5   observed alpha 255

SHAPE, independent of any calibration:
  declared fade-out spans t=194..210 (16 units); of that,
    12/16 units drop only 23/255 of the alpha (a near-flat leg),
    4/16 units drop 200/255 (a cliff).
  captured fade-out: [255, 254, 243, 237, 215, 181, 148, 131, 98, 65, 48, 23, 15, 7]
  per-frame drops:   [1, 11, 6, 22, 34, 33, 17, 33, 33, 17, 25, 8, 8]  -> no near-flat leg
