diff --git a/libopenjpeg/j2k.c b/libopenjpeg/j2k.c
index 3d0fd86e..a0ba1401 100644
--- a/libopenjpeg/j2k.c
+++ b/libopenjpeg/j2k.c
@@ -483,7 +483,7 @@ void j2k_read_qcx(int compno, int len)
 						len - 1 : (len - 1) / 2);
   for (bandno = 0; bandno < numbands; bandno++) {
     int expn, mant;
-    if (tccp->qntsty == J2K_CCP_QNTSTY_NOQNT) {	/* WHY STEPSIZES WHEN NOQNT ? */
+    if (tccp->qntsty == J2K_CCP_QNTSTY_NOQNT) {
       expn = cio_read(1) >> 3;	/* SPqcx_i */
       mant = 0;
     } else {
@@ -494,6 +494,17 @@ void j2k_read_qcx(int compno, int len)
     tccp->stepsizes[bandno].expn = expn;
     tccp->stepsizes[bandno].mant = mant;
   }
+
+  /* Add Antonin : if scalar_derived -> compute other stepsizes */
+
+  if (tccp->qntsty==J2K_CCP_QNTSTY_SIQNT) {
+    for (bandno=1 ; bandno<J2K_MAXBANDS ; bandno++) {
+      tccp->stepsizes[bandno].expn = ((tccp->stepsizes[0].expn)-((bandno-1)/3+1)>0)?(tccp->stepsizes[0].expn)-((bandno-1)/3+1):0;
+      tccp->stepsizes[bandno].mant = tccp->stepsizes[0].mant;
+    }
+  }
+
+  /* ddA */
 }
 
 void j2k_write_qcd()
diff --git a/libopenjpeg/j2k.h b/libopenjpeg/j2k.h
index 637b12b0..a4c4a52f 100644
--- a/libopenjpeg/j2k.h
+++ b/libopenjpeg/j2k.h
@@ -42,7 +42,7 @@
 #define __J2K_H
 
 #define J2K_MAXRLVLS 33		/* Number of maximum resolution level authorized                   */
-#define J2K_MAXBANDS (3*J2K_MAXRLVLS+1)	/* Number of maximum sub-band linked to number of resolution level */
+#define J2K_MAXBANDS (3*J2K_MAXRLVLS-2)	/* Number of maximum sub-band linked to number of resolution level */
 
 #define J2K_CP_CSTY_PRT 0x01
 #define J2K_CP_CSTY_SOP 0x02
@@ -97,7 +97,7 @@ typedef struct {
   int cblksty;			/* code-block coding style               */
   int qmfbid;			/* discrete wavelet transform identifier */
   int qntsty;			/* quantisation style                    */
-  j2k_stepsize_t stepsizes[J2K_MAXBANDS];	/* stepsizes used for quantisation       */
+  j2k_stepsize_t stepsizes[J2K_MAXBANDS];	/* stepsizes used for quantization       */
   int numgbits;			/* number of guard bits                  */
   int roishift;			/* Region Of Interest shift              */
   int prcw[J2K_MAXRLVLS];	/* Precinct width                        */