var
  iImgWidth, iImgHeight: Integer;
const
  DPI = 200;
begin
  iImgWidth := iImgWidth;
  iImgHeight := iImgHeight;
  iImgWidth := iImgWidth * DPI;
  iImgHeight := iImgHeight * DPI;

  ievMain.Proc.ImageResize(iImgWidth, iImgHeight, iehLeft, ievTop);
  ievMain.Proc.Fill(clWhite);
  ievMain.IO.Params.Dpi := DPI;
  ievMain.ChangeResolution(DPI, rfBicubic);

  ievMain.Bitmap.PixelFormat := pf24bit; // <-- This line raises Error!

  ievMain.Layers[0].Locked := True;
  ievMain.Layers[0].Selectable := False;
  ievMain.Update;