Hi, by running this code, for 'val3-val1' it returns zero, would you please help me solve this weird problem?!

xdd=-4.5 ydd=-4.5

xmid=6 ymid=6

xd=xdd+xmid; yd=ydd+ymid;

A=imread('1.tiff')

xd1=floor(xd); xd2=ceil(xd); yd1=floor(yd); yd2=ceil(yd);

val1=A(xd1,yd1) val2=A(xd2,yd1) val3=A(xd1,yd2) val4=A(xd2,yd2)

xd_abs=abs(xd) yd_abs=abs(yd)

xd_fract=xd_abs-floor(xd_abs) yd_fract=xd_abs-floor(xd_abs)

new_row0 = ((val3 - val1) * xd_fract) + val1 new_row1 = ((val4 - val2) * xd_fract) + val2

new_pxl_val =((new_row1 - new_row0) * yd_fract) + new_row0

where A =

253  203  187  186  230  251  225  228  250  254  253
243  145  164  141  184  246  206  212  240  255  252
243  152  167  147  190  243  192  197  235  255  252
249  122   98   90  189  225  179  218  230  253  253
248  127  110  102  189  231  196  217  226  252  253
248  126  109   97  182  248  218  231  234  255  252
248  126  109   97  184  238  216  217  206  255  252
248  126  108  100  187  254  240  239  228  255  252
248  128  110  101  189  247  223  244  239  255  252
248  121  102   92  185  247  223  229  221  255  251
250  159  144  138  203  255  250  240  237  254  252

val1 =

253

val3 =

203

 val3-val1

ans =

    0

Answer 1

[Star Strider]

Check the type of integers you have. If they are unsigned integers (as they would be for images), no negative values exist by definition. All operations that evaluate to <0 will evaluate to zero. You have to cast them as int16 or double if you want negative values.

[Star Strider]

Nika Commented:

Thanks, everything was due to variable types, I changed to double so now it's working.

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My pleasure!

Answer 2

[Ben11]

When I run your code I get -50. Did you do a clear before running the code? Here is what I used:

clear
clc

A = [253  203  187  186  230  251  225  228  250  254  253
243  145  164  141  184  246  206  212  240  255  252
243  152  167  147  190  243  192  197  235  255  252
249  122   98   90  189  225  179  218  230  253  253
248  127  110  102  189  231  196  217  226  252  253
248  126  109   97  182  248  218  231  234  255  252
248  126  109   97  184  238  216  217  206  255  252
248  126  108  100  187  254  240  239  228  255  252
248  128  110  101  189  247  223  244  239  255  252
248  121  102   92  185  247  223  229  221  255  251
250  159  144  138  203  255  250  240  237  254  252];

xdd=-4.5 ;
ydd=-4.5;

xmid=6;
ymid=6;

xd=xdd+xmid;
yd=ydd+ymid;

xd1=floor(xd); xd2=ceil(xd); yd1=floor(yd); yd2=ceil(yd);

val1=A(xd1,yd1);

val2=A(xd2,yd1);
val3=A(xd1,yd2);
val4=A(xd2,yd2);

xd_abs=abs(xd); 
yd_abs=abs(yd);

xd_fract=xd_abs-floor(xd_abs); 
yd_fract=xd_abs-floor(xd_abs);

new_row0 = ((val3 - val1) * xd_fract) + val1; 
new_row1 = ((val4 - val2) * xd_fract) + val2;

new_pxl_val =((new_row1 - new_row0) * yd_fract) + new_row0;

val3 - val1

ans =

   -50

[Nika]

Thanks, everything was due to variable types, I changed to double so now it's working.