--- /dev/null
+#include "pysam.h"
+
+#include <ctype.h>
+#include "bam.h"
+
+/*!
+ @abstract Get the color encoding the previous and current base
+ @param b pointer to an alignment
+ @param i The i-th position, 0-based
+ @return color
+
+ @discussion Returns 0 no color information is found.
+ */
+char bam_aux_getCSi(bam1_t *b, int i)
+{
+ uint8_t *c = bam_aux_get(b, "CS");
+ char *cs = NULL;
+
+ // return the base if the tag was not found
+ if(0 == c) return 0;
+
+ cs = bam_aux2Z(c);
+ // adjust for strandedness and leading adaptor
+ if(bam1_strand(b)) i = strlen(cs) - 1 - i;
+ else i++;
+ return cs[i];
+}
+
+/*!
+ @abstract Get the color quality of the color encoding the previous and current base
+ @param b pointer to an alignment
+ @param i The i-th position, 0-based
+ @return color quality
+
+ @discussion Returns 0 no color information is found.
+ */
+char bam_aux_getCQi(bam1_t *b, int i)
+{
+ uint8_t *c = bam_aux_get(b, "CQ");
+ char *cq = NULL;
+
+ // return the base if the tag was not found
+ if(0 == c) return 0;
+
+ cq = bam_aux2Z(c);
+ // adjust for strandedness
+ if(bam1_strand(b)) i = strlen(cq) - 1 - i;
+ return cq[i];
+}
+
+char bam_aux_nt2int(char a)
+{
+ switch(toupper(a)) {
+ case 'A':
+ return 0;
+ break;
+ case 'C':
+ return 1;
+ break;
+ case 'G':
+ return 2;
+ break;
+ case 'T':
+ return 3;
+ break;
+ default:
+ return 4;
+ break;
+ }
+}
+
+char bam_aux_ntnt2cs(char a, char b)
+{
+ a = bam_aux_nt2int(a);
+ b = bam_aux_nt2int(b);
+ if(4 == a || 4 == b) return '4';
+ return "0123"[(int)(a ^ b)];
+}
+
+/*!
+ @abstract Get the color error profile at the give position
+ @param b pointer to an alignment
+ @return the original color if the color was an error, '-' (dash) otherwise
+
+ @discussion Returns 0 no color information is found.
+ */
+char bam_aux_getCEi(bam1_t *b, int i)
+{
+ int cs_i;
+ uint8_t *c = bam_aux_get(b, "CS");
+ char *cs = NULL;
+ char prev_b, cur_b;
+ char cur_color, cor_color;
+
+ // return the base if the tag was not found
+ if(0 == c) return 0;
+
+ cs = bam_aux2Z(c);
+
+ // adjust for strandedness and leading adaptor
+ if(bam1_strand(b)) { //reverse strand
+ cs_i = strlen(cs) - 1 - i;
+ // get current color
+ cur_color = cs[cs_i];
+ // get previous base. Note: must rc adaptor
+ prev_b = (cs_i == 1) ? "TGCAN"[(int)bam_aux_nt2int(cs[0])] : bam_nt16_rev_table[bam1_seqi(bam1_seq(b), i+1)];
+ // get current base
+ cur_b = bam_nt16_rev_table[bam1_seqi(bam1_seq(b), i)];
+ }
+ else {
+ cs_i=i+1;
+ // get current color
+ cur_color = cs[cs_i];
+ // get previous base
+ prev_b = (0 == i) ? cs[0] : bam_nt16_rev_table[bam1_seqi(bam1_seq(b), i-1)];
+ // get current base
+ cur_b = bam_nt16_rev_table[bam1_seqi(bam1_seq(b), i)];
+ }
+
+ // corrected color
+ cor_color = bam_aux_ntnt2cs(prev_b, cur_b);
+
+ if(cur_color == cor_color) {
+ return '-';
+ }
+ else {
+ return cur_color;
+ }
+}