AREA UNDER the CURVE

Hi every one..

How to calculate area under curve? i used this code

surf(X(59:69,71:85))

the curve picture like below.

this is my data

529 589 644 707 796 940 1072 1143 1128 989 805 632 509 439 408

486 579 702 881 1177 1560 1895 2034 1908 1537 1112 773 562 462 421

468 600 808 1170 1773 2572 3190 3356 3050 2343 1540 942 622 484 442

474 642 952 1538 2487 3649 4480 4713 4272 3215 1990 1126 682 502 449

493 700 1102 1866 3056 4328 5239 5480 5006 3816 2346 1268 719 519 465

509 735 1153 1956 3151 4394 5291 5540 5141 4012 2454 1289 723 526 472

504 704 1068 1731 2736 3852 4682 4898 4557 3474 2125 1139 671 505 451

485 637 901 1363 2073 2902 3508 3634 3245 2394 1470 866 568 456 420

477 578 745 1020 1434 1926 2200 2193 1897 1414 940 637 480 420 398

474 536 635 780 992 1190 1258 1197 1062 853 656 519 442 407 390

467 501 554 636 736 792 781 741 689 606 527 480 450 420 395

Answer 1

[Star Strider]

Defining your matrix as ‘M’, use the trapz function twice, once in each dimension:

AUC = trapz(trapz(M))

producing:

AUC =
                 236001.75

[mohd akmal masud]

How define matrix M?

[Star Strider]

The ‘M’ matrix is the posted data in a matrix:

M = [529   589   644   707   796   940  1072  1143  1128   989   805   632   509   439   408  
     486   579   702   881  1177  1560  1895  2034  1908  1537  1112   773   562   462   421  
     468   600   808  1170  1773  2572  3190  3356  3050  2343  1540   942   622   484   442  
     474   642   952  1538  2487  3649  4480  4713  4272  3215  1990  1126   682   502   449  
     493   700  1102  1866  3056  4328  5239  5480  5006  3816  2346  1268   719   519   465  
     509   735  1153  1956  3151  4394  5291  5540  5141  4012  2454  1289   723   526   472  
     504   704  1068  1731  2736  3852  4682  4898  4557  3474  2125  1139   671   505   451  
     485   637   901  1363  2073  2902  3508  3634  3245  2394  1470   866   568   456   420  
     477   578   745  1020  1434  1926  2200  2193  1897  1414   940   637   480   420   398  
     474   536   635   780   992  1190  1258  1197  1062   853   656   519   442   407   390  
     467   501   554   636   736   792   781   741   689   606   527   480   450   420   395];

[mohd akmal masud]

I see...

[mohd akmal masud]

I think this is not area under curve, but this is summation of total pixel value.

AUC = trapz(trapz(M))
producing: 
AUC =
                 236001.75

[Star Strider]

Without the ‘x’ and ‘y’ vectors (that define the x and y coordinates), trapz defaults to 1 for the intervals of the independent variable.

Defining the x and y vectors gives an appropriately different result.

Example —

x = linspace(1, 500, size(M,1));
y = linspace(-5, 5, size(M,2));

AUC = trapz(y,trapz(x,M))

produces:

AUC =
         8411776.66071429

See the documentation on trapz for details.

[mohd akmal masud]

oh i see..but how to extract all the pixel value? i have try thid code but the result not show the pixel value

X = dicomread('128X128','frames',16);
Y=find(X(58:70,70:84));

[Star Strider]

There was nothing about image processing in your original question.

Note that:

Y=find(X(58:70,70:84));

will only return the indices (that will be 1:13 and 1:15), and nothing else.

It may be best for you to ask a new Question specifically about image processing of DICOM images if that more directly relates to the actual problem you would like to solve.