Plot[Max[Min[x,255],0],{x,-100,350},BaseStyle->{Bold,14},PlotStyle->{Blue,AbsoluteThickness[3]},AxesOrigin->{-100,0},PlotLabel->"Scaled->False",AxesLabel->{"input","output"},Ticks->{Automatic,Union[Table[32k,{k,0,7}],{255}]},AspectRatio->Automatic]

Graphics[{Red,AbsoluteThickness[3],Line[{{-100,0},{350,255}}]},BaseStyle->{Bold,14},AxesOrigin->{-100,0},Axes->True,PlotLabel->"Scaled->True",AxesLabel->{"input","output"},Ticks->{Automatic,Union[Table[32k,{k,0,7}],{255}]},AspectRatio->Automatic]

Inputs between 200 and 255:

Graphics[{Red,AbsoluteThickness[3],Line[{{200,0},{255,255}}]},BaseStyle->{Bold,14},AxesOrigin->{150,0},Axes->True,PlotLabel->"Scaled->True",AxesLabel->{"input","output"},Ticks->{Automatic,Union[Table[32k,{k,0,7}],{255}]},AspectRatio->Automatic]

Graphics[{Red,AbsoluteThickness[3],Line[{{200,200},{255,255}}]},BaseStyle->{Bold,14},AxesOrigin->{150,0},Axes->True,PlotLabel->"Scaled->False",AxesLabel->{"input","output"},Ticks->{Automatic,Union[Table[32k,{k,0,7}],{255}]},AspectRatio->Automatic]