data2 = Table[N[Sign[Sin[10 2 Pi n/256]]],  {n, 256}];

ListPlot[ data2,  PlotJoined  ->  True]

ListPlot[ Abs[Fourier[data2]],  PlotJoined  ->  True,  
      PlotRange  ->  All]

data3 = 
      Table[N[1 + Sign[-0.8 + Sin[10 2 Pi n/256]]],  {n, 256}];

ListPlot[ data3,  PlotJoined  ->  True]

ListPlot[ Abs[Fourier[data3]],  PlotJoined  ->  True,  
      PlotRange  ->  All]

data4 = 
      Table[Sin[10 2 Pi i/256] Sin[10 2 Pi j/256],  {i,  0,  256}, 
         {j,  0,  256}];

ListDensityPlot[data4,  Mesh  ->  False];  data  =   .

data4 = 
      Table[Sign[-0.8 + Sin[10 2 Pi i/256] Sin[10 2 Pi j/256]], 
         {i,  0,  256},  {j,  0,  256}];

ListDensityPlot[data4,  Mesh  ->  False];  data  =   .

data5  =  
      Table[Sin[10*2*Pi*i/128]*Sin[10*2*Pi*j/128],  {i,  0,  128}, 
         {j,  0,  128}];

ListDensityPlot[data5,  Mesh  ->  False];  data  =   .

data6 = Fourier[data5];

ListDensityPlot[Abs[data6],  PlotRange  ->  All,  
      Mesh  ->  False];

data7  =  
      Table[Sign[-0.9 + Sin[10*2*Pi*i/128]*Sin[10*2*Pi*j/128]], 
         {i,  0,  128},  {j,  0,  128}];

ListDensityPlot[data7,  Mesh  ->  False];

data8 = Fourier[data7];

ListDensityPlot[Abs[data8],  PlotRange  ->  {0, 4},  
      Mesh  ->  False];

Max[Abs[data8]]