Okay, first of a point in ROC space is spanned by true positive rate and false positive rate. Now you need to decide if you want to plot a curve for each image or maybe a curve for the complete data (add all together).
In your case you only have 2 thresholds, so that makes the "curves" a little awkward because you only have 4 points total, but whatever. Lets say you want a curve for image1: tp1<-1066 fp1<-70 fn1<-116 tn1<-0 tpr1<-tp1/(tp1+fn1) fpr1<-fp1/(fp1+tn1) tp2<-446 fp2<-41 fn2<-55 tn2<-0 tpr2<-tp2/(tp2+fn2) fpr2<-fp2/(fp2+tn2) plot(0,0,type="n",ylim=c(0,1),xlim=c(0,1)) points(c(0,fpr1,fpr2,1),c(0,tpr1,tpr2,1)) lines(c(0,fpr1,fpr2,1),c(0,tpr1,tpr2,1)) Now i have to say though, after taking a look at that data you provided: THE DATA IS WRONG If you add up all values (tp+tn+fp+fn), the number in threshold 2 is lower than in threshold 1. It needs to be the same, so what the hell have you DONE? ^^ greetings Jessi On 16.08.2012, at 17:49, Jessica Streicher wrote: > To clarify: > > Is TN = 0 or do you not know TN (N)? > > On 16.08.2012, at 11:51, vjyns wrote: > >> Hi, >> >> I want to plot ROC curve for my detection algorithm which detects >> features in different images at two different thresholds. >> >> 6 different images used and obtained tp, fp and fn. No tn in my case. >> >> in first threshold run i obtained 6 values of tp,fp and fn. In second >> threshold run agian i got 6 more. >> >> i had calculated tpr and fpr. How to plot ROC in this case. >> >> Is this possible to plot ROC curve in this case? If s, please guide me to >> plot that. >> >> thank you. >> >> http://r.789695.n4.nabble.com/file/n4640474/in1.png >> >> >> >> -- >> View this message in context: >> http://r.789695.n4.nabble.com/no-true-negative-data-need-roc-curve-tp4640474.html >> Sent from the R help mailing list archive at Nabble.com. >> >> ______________________________________________ >> R-help@r-project.org mailing list >> https://stat.ethz.ch/mailman/listinfo/r-help >> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html >> and provide commented, minimal, self-contained, reproducible code. > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.