In[]:=
nm=Image
0.6
0.5
0.5
0.1
0.2
0.6
0.6
0.9
0.1
0.8
0.4
0.2
0.7
0.5
0.1
0.5

Out[]=
In[]:=
idata=ImageData[nm]
Out[]=
{{0.6,0.5,0.5,0.1},{0.2,0.6,0.6,0.9},{0.1,0.8,0.4,0.2},{0.7,0.5,0.1,0.5}}
In[]:=
part=Partition[Flatten[idata],4]
Out[]=
{{0.6,0.5,0.5,0.1},{0.2,0.6,0.6,0.9},{0.1,0.8,0.4,0.2},{0.7,0.5,0.1,0.5}}
In[]:=
ListPlot3D[part](*part=Partition[Flatten[idata],4]*)
Out[]=
In[]:=
ListPlot3D[part](*part=Partition[Flatten[idata],3]*)
Out[]=