diff --git a/backend/snapscan-scsi.c b/backend/snapscan-scsi.c
index b1c8c96a3..bc294be7a 100644
--- a/backend/snapscan-scsi.c
+++ b/backend/snapscan-scsi.c
@@ -78,11 +78,13 @@ static SANE_Status sense_handler (int scsi_fd, u_char * result, void *arg)
         pss->asi1 = result[18];
         pss->asi2 = result[19];
     }
-
     if ((result[0] & 0x80) == 0)
     {
         DBG (DL_DATA_TRACE, "%s: sense key is invalid.\n", me);
         return SANE_STATUS_GOOD;    /* sense key invalid */
+    } else {
+        DBG (DL_DATA_TRACE, "%s: sense key: 0x%02x, asc: 0x%02x, ascq: 0x%02x, i1: 0x%02x, i2: 0x%02x\n",
+        me, sense, asc, ascq, result[18], result[19]);
     }
 
     switch (sense)
@@ -90,49 +92,61 @@ static SANE_Status sense_handler (int scsi_fd, u_char * result, void *arg)
     case 0x00:
         /* no sense */
         sense_str = "No sense.";
+        DBG (DL_MINOR_INFO, "%s: %s\n", me, sense_str);
         break;
     case 0x02:
         /* not ready */
         sense_str = "Not ready.";
+        DBG (DL_MINOR_INFO, "%s: %s\n", me, sense_str);
         if (asc == 0x04  &&  ascq == 0x01)
         {
             /* warming up; byte 18 contains remaining seconds */
             as_str = "Logical unit is in process of becoming ready.";
+            DBG (DL_MINOR_INFO, "%s: %s (%d seconds)\n", me, as_str, result[18]);
             status = SANE_STATUS_DEVICE_BUSY;
+        DBG (DL_MINOR_INFO, "%s: %s\n", me, sense_str);
         }
         break;
     case 0x04:
         /* hardware error */
         sense_str = "Hardware error.";
         /* byte 18 and 19 detail the hardware problems */
+        DBG (DL_MINOR_INFO, "%s: %s (0x%02x, 0x%02x)\n", me, sense_str, result[18],
+            result[19]);
         status = SANE_STATUS_IO_ERROR;
         break;
     case 0x05:
         /* illegal request */
         sense_str = "Illegal request.";
+        DBG (DL_MINOR_INFO, "%s: %s\n", me, sense_str);
         if (asc == 0x25 && ascq == 0x00)
             as_str = "Logical unit not supported.";
+            DBG (DL_MINOR_INFO, "%s: %s\n", me, as_str);
         status = SANE_STATUS_IO_ERROR;
         break;
     case 0x09:
         /* process error */
         sense_str = "Process error.";
+        DBG (DL_MINOR_INFO, "%s: %s\n", me, sense_str);
         if (asc == 0x00 && ascq == 0x05)
         {
             /* no documents in ADF */
             as_str = "End of data detected.";
+            DBG (DL_MINOR_INFO, "%s: %s\n", me, as_str);
             status = SANE_STATUS_NO_DOCS;
         }
         else if (asc == 0x3b && ascq == 0x05)
         {
             /* paper jam in ADF */
             as_str = "Paper jam.";
+            DBG (DL_MINOR_INFO, "%s: %s\n", me, as_str);
             status = SANE_STATUS_JAMMED;
         }
         else if (asc == 0x3b && ascq == 0x09)
         {
             /* scanning area exceeds end of paper in ADF */
             as_str = "Read past end of medium.";
+            DBG (DL_MINOR_INFO, "%s: %s\n", me, as_str);
             status = SANE_STATUS_EOF;
         }
         break;
@@ -163,7 +177,8 @@ static SANE_Status open_scanner (SnapScan_Scanner *pss)
         }
         else
         {
-            status = snapscani_usb_open (pss->devname, &(pss->fd));
+            status = snapscani_usb_open (pss->devname, &(pss->fd),
+                sense_handler, (void *) pss);
         }
     }
     else
@@ -435,17 +450,20 @@ static SANE_Status inquiry (SnapScan_Scanner *pss)
     default:
     {
         signed char min_diff;
+        u_char r_off, g_off, b_off;
         signed char g = (pss->buf[INQUIRY_G2R_DIFF] & 0x80) ? -(pss->buf[INQUIRY_G2R_DIFF] & 0x7F) : pss->buf[INQUIRY_G2R_DIFF];
         signed char b = (pss->buf[INQUIRY_B2R_DIFF] & 0x80) ? -(pss->buf[INQUIRY_B2R_DIFF] & 0x7F) : pss->buf[INQUIRY_B2R_DIFF];
         DBG (DL_DATA_TRACE, "%s: G2R_DIFF: %d\n", me, pss->buf[INQUIRY_G2R_DIFF]);
         DBG (DL_DATA_TRACE, "%s: B2R_DIFF: %d\n", me, pss->buf[INQUIRY_B2R_DIFF]);
 
         min_diff = MIN (MIN (b, g), 0);
-
-        pss->chroma_offset[R_CHAN] = (u_char) (0 - min_diff);
-        pss->chroma_offset[G_CHAN] = (u_char) (g - min_diff);
-        pss->chroma_offset[B_CHAN] = (u_char) (b - min_diff);
-        pss->chroma = abs(min_diff);
+        r_off = (u_char) (0 - min_diff);
+        g_off = (u_char) (g - min_diff);
+        b_off = (u_char) (b - min_diff);
+        pss->chroma_offset[R_CHAN] = r_off;
+        pss->chroma_offset[G_CHAN] = g_off;
+        pss->chroma_offset[B_CHAN] = b_off;
+        pss->chroma = MAX(MAX(r_off, g_off), b_off);
         DBG (DL_DATA_TRACE,
             "%s: Chroma offsets=%d; Red=%u, Green:=%u, Blue=%u\n",
             me, pss->chroma,
@@ -799,19 +817,21 @@ static SANE_Status set_window (SnapScan_Scanner *pss)
        &&
        pss->pdev->model != VUEGO310S
        &&
-       pss->pdev->model != VUEGO610S)
-      {
-    pc[SET_WINDOW_P_DEBUG_MODE] = 2;        /* use full 128k buffer */
-    pc[SET_WINDOW_P_GAMMA_NO] = 0x01;        /* downloaded table */
-      }
-    if (pss->preview) {
-        source = 0x20 + 0x40;
-
-    } else {
-    source = 0x20 + 0x80;
+       pss->pdev->model != VUEGO610S
+    ) {
+        pc[SET_WINDOW_P_DEBUG_MODE] = 2;        /* use full 128k buffer */
+        pc[SET_WINDOW_P_GAMMA_NO] = 0x01;        /* downloaded table */
+    }
+    source = 0x20;
+    if (pss->preview) {
+        source |= 0x80; /* no high quality */
+    } else {
+        source |= 0x40; /* no preview */
+    }
+
+    if (pss->source == SRC_TPO) {
+        source |= 0x08;
     }
-    if (pss->source == SRC_TPO)
-    source |= 0x08;
     pc[SET_WINDOW_P_OPERATION_MODE] = source;
     DBG (DL_DATA_TRACE, "%s: operation mode set to %d\n", me, (int) source);
     pc[SET_WINDOW_P_RED_UNDER_COLOR] = 0xff;    /* defaults */
@@ -918,33 +938,29 @@ static SANE_Status wait_scanner_ready (SnapScan_Scanner *pss)
     for (retries = 5; retries; retries--)
     {
         status = test_unit_ready (pss);
-        if (status == SANE_STATUS_GOOD)
+        switch (status)
         {
-            status = request_sense (pss);
-            switch (status)
+        case SANE_STATUS_GOOD:
+            return status;
+        case SANE_STATUS_DEVICE_BUSY:
+            /* first additional sense byte contains time to wait */
             {
-            case SANE_STATUS_GOOD:
-                return status;
-            case SANE_STATUS_DEVICE_BUSY:
-                /* first additional sense byte contains time to wait */
-                {
-                    int delay = pss->asi1 + 1;
-                    DBG (DL_INFO,
-                        "%s: scanner warming up. Waiting %ld seconds.\n",
-                         me, (long) delay);
-                    sleep (delay);
-                }
-                break;
-            case SANE_STATUS_IO_ERROR:
-                /* hardware error; bail */
-                DBG (DL_MAJOR_ERROR, "%s: hardware error detected.\n", me);
-                return status;
-            default:
-                DBG (DL_MAJOR_ERROR,
-                     "%s: unhandled request_sense result; trying again.\n",
-                     me);
-                break;
+                int delay = pss->asi1 + 1;
+                DBG (DL_INFO,
+                    "%s: scanner warming up. Waiting %ld seconds.\n",
+                    me, (long) delay);
+                sleep (delay);
             }
+            break;
+        case SANE_STATUS_IO_ERROR:
+            /* hardware error; bail */
+            DBG (DL_MAJOR_ERROR, "%s: hardware error detected.\n", me);
+            return status;
+        default:
+            DBG (DL_MAJOR_ERROR,
+                "%s: unhandled request_sense result; trying again.\n",
+                me);
+            break;
         }
     }
 
@@ -1159,11 +1175,28 @@ static SANE_Status download_firmware(SnapScan_Scanner * pss)
 
 /*
  * $Log$
- * Revision 1.8  2001/10/22 22:14:20  oliverschwartz
- * Limit number of scan lines for quality calibration to fit in SCSI buffer (thanks to Mikko Työläjärvi)
+ * Revision 1.9  2001/12/17 22:51:49  oliverschwartz
+ * Update to snapscan-20011212 (snapscan 1.4.3)
  *
- * Revision 1.7  2001/10/12 21:19:13  oliverschwartz
- * update to snapscan-20011012
+ * Revision 1.25  2001/12/12 19:44:59  oliverschwartz
+ * Clean up CVS log
+ *
+ * Revision 1.24  2001/12/09 23:01:00  oliverschwartz
+ * - use sense handler for USB
+ * - fix scan mode
+ *
+ * Revision 1.23  2001/12/08 11:53:31  oliverschwartz
+ * - Additional logging in sense handler
+ * - Fix wait_scanner_ready() if device reports busy
+ * - Fix scanning mode (preview/normal)
+ *
+ * Revision 1.22  2001/11/27 23:16:17  oliverschwartz
+ * - Fix color alignment for SnapScan 600
+ * - Added documentation in snapscan-sources.c
+ * - Guard against TL_X < BR_X and TL_Y < BR_Y
+ *
+ * Revision 1.21  2001/10/21 08:49:37  oliverschwartz
+ * correct number of scan lines for calibration thanks to Mikko Työläjärvi
  *
  * Revision 1.20  2001/10/12 20:54:04  oliverschwartz
  * enable gamma correction for Snapscan 1236, e20 and e50 scanners
@@ -1205,15 +1238,6 @@ static SANE_Status download_firmware(SnapScan_Scanner * pss)
  * Applying Mikael Magnusson patch concerning Gamma correction
  * Support for 1212U_2
  *
- * Revision 1.3  2001/03/04 16:37:57  mikael
- * Remove brightness and contrast settings in window.
- *
- * Revision 1.2  2001/02/16 18:32:28  mikael
- * impl calibration, signed position, increased buffer size
- *
- * Revision 1.1.1.1  2001/02/10 17:09:29  mikael
- * Imported from snapscan-11282000.tar.gz
- *
  * Revision 1.9  2000/11/10 01:01:59  sable
  * USB (kind of) autodetection
  *
@@ -1239,19 +1263,4 @@ static SANE_Status download_firmware(SnapScan_Scanner * pss)
  * Revision 1.2  2000/10/13 03:50:27  cbagwell
  * Updating to source from SANE 1.0.3.  Calling this versin 1.1
  *
- * Revision 1.3  2000/08/12 15:09:34  pere
- * Merge devel (v1.0.3) into head branch.
- *
- * Revision 1.1.2.3  2000/07/17 21:37:27  hmg
- * 2000-07-17  Henning Meier-Geinitz <hmg@gmx.de>
- *
- *     * backend/snapscan.c backend/snapscan-scsi.c: Replace C++ comment
- *       with C comment.
- *
- * Revision 1.1.2.2  2000/07/13 04:47:44  pere
- * New snapscan backend version dated 20000514 from Steve Underwood.
- *
- * Revision 1.2.1  2000/05/14 13:30:20  coppice
- * Added history log to pre-existing code. Some reformatting and minor
- * tidying.
  * */
diff --git a/backend/snapscan-sources.c b/backend/snapscan-sources.c
index 39134a45e..c79bdd65c 100644
--- a/backend/snapscan-sources.c
+++ b/backend/snapscan-sources.c
@@ -50,6 +50,61 @@
 /* $Id$
    SnapScan backend data sources (implementation) */
 
+/**************************************************************************************
+If you get confused from all the structs (like I did when I first saw them),
+think of it as "C++ in C". If you're accustomed to OO and UML maybe the
+following diagram helps you to make sense of it:
+
+                       ------------------------
+                       !        Source        !
+                       ------------------------
+                       !pss: SnapScan_Scanner*!
+                       ------------------------   +psub
+                       !init() = 0            !-----------------
+                       !remaining() = 0       !                !
+                       !bytesPerLine()        !                !
+                       !pixelsPerLine()       !                !
+                       !get() = 0             !                !{TransformerSource forwards
+                       !done() = 0            !                ! function calls to corres-
+                       ------------------------                ! ponding functions in psub}
+                                   ^                           !
+                                  /_\                          !
+                                   !                           !
+       --------------------------------------------------     /\
+       !               !                !               !     \/
+-------------    -------------    -------------    -------------------
+!SCSISource !    ! FDSource  !    !BufSource  !    !TransformerSource!
+=============    =============    =============    ===================
+!remaining()!    !remaining()!    !remaining()!    !init()           !
+!get()      !    !get()      !    !get()      !    !remaining()      !
+!done()     !    !done()     !    !done()     !    !bytesPerLine()   !
+!init()     !    !init()     !    !init()     !    !pixelsPerLine()  !
+-------------    -------------    -------------    !get()            !
+                                                   !done()           !
+                                                   -------------------
+                                                            ^
+                                                           /_\
+                                                            !
+                                       ------------------------------------
+                                       !                 !                !
+                              ----------------    -------------    -------------
+                              !   Expander   !    ! RGBRouter !    !  Inverter !
+                              ================    =============    =============
+                              !remaining()   !    !remaining()!    !remaining()!
+                              !bytesPerLine()!    !get()      !    !get()      !
+                              !get()         !    !done()     !    !done()     !
+                              !done()        !    !init()     !    !init()     !
+                              !init()        !    -------------    -------------
+                              ----------------
+All instances of the descendants of TransformerSource can be chained together. For
+color scanning, a typical source chain would consist of an RGBRouter sitting on top
+of a SCSISource. In the get() method, RGBRouter will then call the get() method of
+the subsource, process the data and return it.
+
+I hope this makes sense to you (and I got the right idea of the original author's
+intention).
+***********************************************************************************/
+
 #ifndef __FUNCTION__
 #define __FUNCTION__ "(undef)"
 #endif
@@ -910,8 +965,16 @@ static SANE_Status create_source_chain (SnapScan_Scanner *pss,
 
 /*
  * $Log$
- * Revision 1.5  2001/10/09 09:45:12  oliverschwartz
- * update snapscan to snapshot 20011008
+ * Revision 1.6  2001/12/17 22:51:49  oliverschwartz
+ * Update to snapscan-20011212 (snapscan 1.4.3)
+ *
+ * Revision 1.18  2001/12/12 19:44:59  oliverschwartz
+ * Clean up CVS log
+ *
+ * Revision 1.17  2001/11/27 23:16:17  oliverschwartz
+ * - Fix color alignment for SnapScan 600
+ * - Added documentation in snapscan-sources.c
+ * - Guard against TL_X < BR_X and TL_Y < BR_Y
  *
  * Revision 1.16  2001/10/08 18:22:02  oliverschwartz
  * - Disable quality calibration for Acer Vuego 310F
@@ -946,15 +1009,6 @@ static SANE_Status create_source_chain (SnapScan_Scanner *pss,
  * Applying Mikael Magnusson patch concerning Gamma correction
  * Support for 1212U_2
  *
- * Revision 1.3  2001/03/04 16:53:21  mikael
- * Reading absolute max from SNAPSCAN 1212U
- *
- * Revision 1.2  2001/02/16 18:32:28  mikael
- * impl calibration, signed position, increased buffer size
- *
- * Revision 1.1.1.1  2001/02/10 17:09:29  mikael
- * Imported from snapscan-11282000.tar.gz
- *
  * Revision 1.8  2000/11/28 03:55:07  cbagwell
  * Reverting a fix to RGBRouter_remaining to original fix.  This allows
  * most scanners to scan at 600 dpi by ignoring insufficent data in
@@ -982,15 +1036,4 @@ static SANE_Status create_source_chain (SnapScan_Scanner *pss,
  *
  * Revision 1.2  2000/10/13 03:50:27  cbagwell
  * Updating to source from SANE 1.0.3.  Calling this versin 1.1
- *
- * Revision 1.3  2000/08/12 15:09:35  pere
- * Merge devel (v1.0.3) into head branch.
- *
- * Revision 1.1.2.2  2000/07/13 04:47:45  pere
- * New snapscan backend version dated 20000514 from Steve Underwood.
- *
- * Revision 1.2.1  2000/05/14 13:30:20  coppice
- * Added history log to pre-existing code.Some reformatting.
- * R, G and B images now merge correctly. There are still some outstanding
- * issues in this area, but its a lot more usable than before.
  * */
diff --git a/backend/snapscan-sources.h b/backend/snapscan-sources.h
index 57d78acc5..53b705be2 100644
--- a/backend/snapscan-sources.h
+++ b/backend/snapscan-sources.h
@@ -88,8 +88,11 @@ static SANE_Status Source_init (Source *pself,
 
 /*
  * $Log$
- * Revision 1.4  2001/10/09 09:45:13  oliverschwartz
- * update snapscan to snapshot 20011008
+ * Revision 1.5  2001/12/17 22:51:50  oliverschwartz
+ * Update to snapscan-20011212 (snapscan 1.4.3)
+ *
+ * Revision 1.5  2001/12/12 19:44:59  oliverschwartz
+ * Clean up CVS log
  *
  * Revision 1.4  2001/09/18 15:01:07  oliverschwartz
  * - Read scanner id string again after firmware upload
@@ -101,18 +104,6 @@ static SANE_Status Source_init (Source *pself,
  * Applying Mikael Magnusson patch concerning Gamma correction
  * Support for 1212U_2
  *
- * Revision 1.1.1.1  2001/02/10 17:09:29  mikael
- * Imported from snapscan-11282000.tar.gz
- *
  * Revision 1.2  2000/10/13 03:50:27  cbagwell
  * Updating to source from SANE 1.0.3.  Calling this versin 1.1
- *
- * Revision 1.2  2000/08/12 15:09:35  pere
- * Merge devel (v1.0.3) into head branch.
- *
- * Revision 1.1.2.1  2000/07/13 04:47:46  pere
- * New snapscan backend version dated 20000514 from Steve Underwood.
- *
- * Revision 1.1.1  2000/05/14 13:30:20  coppice
- * Added history log to pre-existing code. Some reformatting.
  * */
diff --git a/backend/snapscan-usb.c b/backend/snapscan-usb.c
index df2440866..57df2dc5d 100644
--- a/backend/snapscan-usb.c
+++ b/backend/snapscan-usb.c
@@ -4,7 +4,7 @@
   Copyright (C) 2000 Henrik Johansson
  
   Henrik Johansson (henrikjo@post.urfors.se)
-    
+
   This program is free software; you can redistribute it and/or
   modify it under the terms of the GNU General Public License as
   published by the Free Software Foundation; either version 2 of the
@@ -60,6 +60,11 @@
 static int sem_id;
 static struct sembuf sem_wait = { 0, -1, 0 };
 static struct sembuf sem_signal = { 0, 1, 0 };
+static sense_handler_type usb_sense_handler;
+static void* usb_pss;
+
+/* Forward declarations */
+static SANE_Status usb_request_sense(SnapScan_Scanner *pss);
 
 static SANE_Status snapscani_usb_cmd(int fd, const void *src, size_t src_size,
                     void *dst, size_t * dst_size)
@@ -123,7 +128,8 @@ static SANE_Status atomic_usb_cmd(int fd, const void *src, size_t src_size,
 
 }
 
-static SANE_Status snapscani_usb_open(const char *dev, int *fdp)
+static SANE_Status snapscani_usb_open(const char *dev, int *fdp,
+    sense_handler_type sense_handler, void* pss)
 {
     static const char me[] = "snapscani_usb_open";
 
@@ -135,6 +141,8 @@ static SANE_Status snapscani_usb_open(const char *dev, int *fdp)
     }
     semop(sem_id, &sem_signal, 1);
     sanei_usb_init();
+    usb_sense_handler=sense_handler;
+    usb_pss = pss;
     return sanei_usb_open(dev, fdp);
 }
 
@@ -184,24 +192,6 @@ static char *usb_debug_data(char *str,const char *data, int len) {
     return str;
 }
 
-/*
-static int usb_status(char *status_buf) {
-    int status;
-
-    status = (status_buf[1] & STATUS_MASK) >> 1;
-
-    switch(status) {
-    case GOOD:
-        return SANE_STATUS_GOOD;
-    case CHECK_CONDITION:
-    case BUSY:
-        return SANE_STATUS_DEVICE_BUSY;
-    default:
-        return SANE_STATUS_IO_ERROR;
-    }
-}
-*/
-
 #define RETURN_ON_FAILURE(x) if((status = x) != SANE_STATUS_GOOD) return status;
 
 static SANE_Status usb_write(int fd, const void *buf, int n) {
@@ -249,6 +239,7 @@ static SANE_Status usb_read(int fd, void *buf, int n) {
 
 static SANE_Status usb_read_status(int fd, int *scsistatus, int *transaction_status)
 {
+    static const char me[] = "usb_read_status";
     unsigned char status_buf[8];
     int scsistat;
     int status;
@@ -267,6 +258,14 @@ static SANE_Status usb_read_status(int fd, int *scsistatus, int *transaction_sta
     case GOOD:
         return SANE_STATUS_GOOD;
     case CHECK_CONDITION:
+        if (usb_pss != NULL) {
+            return usb_request_sense(usb_pss);
+        } else {
+            DBG (DL_MAJOR_ERROR, "%s: scanner structure not set, returning default error\n",
+                me);
+            return SANE_STATUS_DEVICE_BUSY;
+        }
+        break;
     case BUSY:
         return SANE_STATUS_DEVICE_BUSY;
     default:
@@ -402,15 +401,48 @@ static void dequeue_bq()
     bqelements--;
     DBG(DL_DATA_TRACE, "%s: Busy queue: elements=%d, bqhead=%p, bqtail=%p\n",
         me,bqelements,bqhead,bqtail);
-    
 }
+
+static SANE_Status usb_request_sense(SnapScan_Scanner *pss) {
+    static const char *me = "usb_request_sense";
+    size_t read_bytes = 0;
+    u_char cmd[] = {REQUEST_SENSE, 0, 0, 0, 20, 0};
+    u_char data[20];
+    SANE_Status status;
+
+    read_bytes = 20;
+
+    DBG (DL_CALL_TRACE, "%s\n", me);
+    status = usb_cmd (pss->fd, cmd, sizeof (cmd), data, &read_bytes);
+    if (status != SANE_STATUS_GOOD)
+    {
+        DBG (DL_MAJOR_ERROR, "%s: usb command error: %s\n",
+             me, sane_strstatus (status));
+    }
+    else
+    {
+        if (usb_sense_handler) {
+            status = usb_sense_handler (pss->fd, data, (void *) pss);
+        } else {
+            DBG (DL_MAJOR_ERROR, "%s: No sense handler for USB\n", me);
+            status = SANE_STATUS_UNSUPPORTED;
+        }
+    }
+    return status;
+}
+
 /*
  * $Log$
- * Revision 1.4  2001/10/27 09:08:13  oliverschwartz
- * Check USB vendor IDs to avoid hanging scanners, fix bug in dither matrix computation
+ * Revision 1.5  2001/12/17 22:51:50  oliverschwartz
+ * Update to snapscan-20011212 (snapscan 1.4.3)
  *
- * Revision 1.3  2001/10/10 07:30:06  oliverschwartz
- * fix compiler warnings
+ * Revision 1.15  2001/12/09 23:06:44  oliverschwartz
+ * - use sense handler for USB if scanner reports CHECK_CONDITION
+ *
+ * Revision 1.14  2001/11/16 20:23:16  oliverschwartz
+ * Merge with sane-1.0.6
+ *   - Check USB vendor IDs to avoid hanging scanners
+ *   - fix bug in dither matrix computation
  *
  * Revision 1.13  2001/10/09 22:34:23  oliverschwartz
  * fix compiler warnings
diff --git a/backend/snapscan-usb.h b/backend/snapscan-usb.h
index af56a237a..311101f5b 100644
--- a/backend/snapscan-usb.h
+++ b/backend/snapscan-usb.h
@@ -30,9 +30,12 @@
 #ifndef snapscan_usb_h
 #define snapscan_usb_h
 
+typedef SANE_Status (*sense_handler_type)(int fd, u_char *sense_buffer, void *arg);
+
 static SANE_Status snapscani_usb_cmd(int fd, const void *src, size_t src_size,
                          void *dst, size_t * dst_size);
-static SANE_Status snapscani_usb_open(const char *dev, int *fdp);
+static SANE_Status snapscani_usb_open(const char *dev, int *fdp,
+    sense_handler_type, void*);
 static void snapscani_usb_close(int fd);
 
 /*
@@ -82,11 +85,16 @@ static SANE_Status usb_cmd(int fd, const void *src, size_t src_size,
 
 /*
  * $Log$
- * Revision 1.3  2001/10/27 09:08:14  oliverschwartz
- * Check USB vendor IDs to avoid hanging scanners, fix bug in dither matrix computation
+ * Revision 1.4  2001/12/17 22:51:50  oliverschwartz
+ * Update to snapscan-20011212 (snapscan 1.4.3)
  *
- * Revision 1.2  2001/10/09 09:45:15  oliverschwartz
- * update snapscan to snapshot 20011008
+ * Revision 1.10  2001/12/09 23:06:45  oliverschwartz
+ * - use sense handler for USB if scanner reports CHECK_CONDITION
+ *
+ * Revision 1.9  2001/11/16 20:23:16  oliverschwartz
+ * Merge with sane-1.0.6
+ *   - Check USB vendor IDs to avoid hanging scanners
+ *   - fix bug in dither matrix computation
  *
  * Revision 1.8  2001/09/18 15:01:07  oliverschwartz
  * - Read scanner id string again after firmware upload
diff --git a/backend/snapscan.c b/backend/snapscan.c
index 3c78f503b..e38b4a212 100644
--- a/backend/snapscan.c
+++ b/backend/snapscan.c
@@ -78,7 +78,7 @@
 
 #define EXPECTED_MAJOR       1
 #define MINOR_VERSION        4
-#define BUILD                0
+#define BUILD                3
 
 #include "snapscan.h"
 
@@ -396,6 +396,7 @@ static void init_options (SnapScan_Scanner * ps)
         po[OPT_SCANRES].constraint.word_list = resolutions_300;
         break;
     case SNAPSCANE50:
+    case SNAPSCANE52:
     case PRISA5300:
     case PRISA1240:
         po[OPT_SCANRES].constraint.word_list = resolutions_1200;
@@ -589,8 +590,11 @@ static void init_options (SnapScan_Scanner * ps)
     po[OPT_QUALITY_CAL].constraint_type = SANE_CONSTRAINT_NONE;
     po[OPT_QUALITY_CAL].cap = SANE_CAP_SOFT_SELECT | SANE_CAP_SOFT_DETECT;
     ps->val[OPT_QUALITY_CAL].b = DEFAULT_QUALITY;
-    /* Disable quality calibration option if not supported */
-    if (!(ps->hconfig & HCFG_CAL_ALLOWED)) {
+    /* Disable quality calibration option if not supported
+       Note: Snapscan e52 does not support quality calibration,
+       although HCFG_CAL_ALLOWED is set. */
+    if ((!(ps->hconfig & HCFG_CAL_ALLOWED))
+        || (ps->pdev->model == SNAPSCANE52)) {
         po[OPT_QUALITY_CAL].cap |= SANE_CAP_INACTIVE;
         ps->val[OPT_QUALITY_CAL].b = SANE_FALSE;
     }
@@ -917,57 +921,26 @@ static void gamma_to_sane (int length, u_char *in, SANE_Int *out)
 }
 
 /* dispersed-dot dither matrices; this is discussed in Foley, Van Dam,
-   Feiner and Hughes, 2nd ed., pp 570-571.
- 
+   Feiner and Hughes: Computer Graphics: principles and practice,
+   2nd ed. (Addison-Wesley), pp 570-571.
+
    The function mfDn computes the nth dispersed-dot dither matrix Dn
    given D(n/2) and n; n is presumed to be a power of 2. D8 and D16
    are the matrices of interest to us, since the SnapScan supports
    only 8x8 and 16x16 dither matrices. */
 
-static u_char D2[] =
-{
-    0, 2, 3, 1
-};
+static u_char D2[] ={0, 2, 3, 1};
 
 static u_char D4[16], D8[64], D16[256];
 
-static void mkDn (u_char *Dn, u_char *Dn2, unsigned n)
+static void mkDn (u_char *Dn, u_char *Dn_half, unsigned n)
 {
-    static u_char tmp[256];
-    unsigned n2 = n/2;
-    unsigned nsq = n*n;
-    unsigned i;
-    unsigned r;
-    unsigned imin;
-    unsigned f;
-
-    /* compute 4*D(n/2) */
-    /* Oliver Schwartz, 27 Oct. 2001: Changed code from
-          tmp[i] = (u_char) (4 * Dn2[i]);
-       to
-          tmp[i] = (u_char) (4 * Dn2[i/4]);
-       to avoid illegal indices in Dn2. Don't know if this
-       is the desired algorithm.
-    */
-    for (i = 0;  i < nsq;  i++)
-        tmp[i] = (u_char) (4 * Dn2[i/4]);
-
-    /* now the dither matrix */
-    for (r = 0, imin = 0, f = 0;  r < 2;  r++, imin += n2)
-    {
-        unsigned c;
-        unsigned jmin;
-        for (c = 0, jmin = 0;  c < 2;  c++, jmin += n2, f++)
-        {
-            unsigned i;
-            unsigned i2;
-            unsigned j;
-            unsigned j2;
-            for (i = imin, i2 = 0;  i < imin + n2;  i++, i2++)
-            {
-                for (j = jmin, j2 = 0;  j < jmin + n2;  j++, j2++)
-                    Dn[i * n + j] = (u_char) (tmp[i2 * n2 + j2] + D2[f]);
-            }
+    unsigned int x, y;
+    for (y = 0; y < n; y++) {
+        for (x = 0; x < n; x++) {
+            /* Dn(x,y) = D2(2*x/n, 2*y/n) +4*Dn_half(x%(n/2), y%(n/2)) */
+            Dn[y*n + x] = D2[((int)(2*y/n))*2 + (int)(2*x/n)]
+                          + 4*Dn_half[(y%(n/2))*(n/2) + x%(n/2)];
         }
     }
 }
@@ -1026,7 +999,7 @@ static SANE_Status add_device (SANE_String_Const name)
             name += 3;
             name = sanei_config_skip_whitespace(name);
         }
-        status = snapscani_usb_open (name, &fd);
+        status = snapscani_usb_open (name, &fd, sense_handler, NULL);
         if (status != SANE_STATUS_GOOD)
         {
             DBG (DL_MAJOR_ERROR,
@@ -1129,9 +1102,11 @@ static SANE_Status add_device (SANE_String_Const name)
              me,
              vendor,
              model,
-             "AGFA SnapScan 300, 310, 600 or 1236, "
-             "Acer VUEGO 300, 310S, 610S, or 610plus, "
-             "Acer PRISA 620, 640, 1240, 3300, 4300 or 5300");
+             "AGFA SnapScan 300, 310, 600, 1212, 1236, e20, e25, e26, "
+             "e40, e50, e52 or e60\n"
+             "Acer 300, 310, 610, 610+, "
+             "620, 620+, 640, 1240, 3300, 4300 or 5300\n"
+             "Guillemot MaxiScan A4 Deluxe");
 
         if(bus_type == SCSI)
           {
@@ -1314,7 +1289,7 @@ SANE_Status sane_init (SANE_Int *version_code,
     {
         u_char i;
         for (i = 0;  i < 64;  i++)
-            D8[i] = (u_char) (4 * D8[i] + 3);
+            D8[i] = (u_char) (4 * D8[i] + 2);
     }
 
     return SANE_STATUS_GOOD;
@@ -1660,6 +1635,7 @@ SANE_Status sane_control_option (SANE_Handle h,
 {
     static const char *me = "sane_snapscan_control_option";
     SnapScan_Scanner *pss = h;
+    SnapScan_Device *pdev = pss->pdev;
     static SANE_Status status;
 
     DBG (DL_CALL_TRACE,
@@ -1791,6 +1767,10 @@ SANE_Status sane_control_option (SANE_Handle h,
         }
         break;
     case SANE_ACTION_SET_VALUE:
+        status = sanei_constrain_value(&pss->options[n], v, i);
+        if (status != SANE_STATUS_GOOD) {
+            return status;
+        }
         switch (n)
         {
         case OPT_COUNT:
@@ -1959,9 +1939,9 @@ SANE_Status sane_control_option (SANE_Handle h,
             }
             /* Adjust actual range values to new max values */
             if (pss->brx > pss->pdev->x_range.max)
-                pss->brx = pss->pdev->x_range.max;
+                pss->brx = pss->pdev->x_range.max - pdev->x_range.quant;
             if (pss->bry > pss->pdev->y_range.max)
-                pss->bry = pss->pdev->y_range.max;
+                pss->bry = pss->pdev->y_range.max - pdev->y_range.quant;
             pss->predef_window = pdw_none;
             if (pss->source_s)
                 free (pss->source_s);
@@ -1972,23 +1952,47 @@ SANE_Status sane_control_option (SANE_Handle h,
         case OPT_TLX:
             pss->tlx = *(SANE_Fixed *) v;
             pss->predef_window = pdw_none;
+            if (fabs(pss->tlx - pdev->x_range.max) < pdev->x_range.quant) {
+                pss->tlx -= pdev->x_range.quant;
+            }
+            if (pss->brx < pss->tlx) {
+                pss->brx = pss->tlx + pdev->x_range.quant;
+            }
             if (i)
                 *i = SANE_INFO_RELOAD_PARAMS;
             break;
         case OPT_TLY:
             pss->tly = *(SANE_Fixed *) v;
+            if (fabs(pss->tly - pdev->y_range.max) < pdev->y_range.quant) {
+                pss->tly -= pdev->y_range.quant;
+            }
             pss->predef_window = pdw_none;
+            if (pss->bry < pss->tly) {
+                pss->bry = pss->tly + pdev->y_range.quant;
+            }
             if (i)
                 *i = SANE_INFO_RELOAD_PARAMS;
             break;
         case OPT_BRX:
             pss->brx = *(SANE_Fixed *) v;
+            if (fabs(pss->brx - pdev->x_range.min) < pdev->x_range.quant) {
+                pss->brx += pdev->x_range.quant;
+            }
+            if (pss->brx < pss->tlx) {
+                pss->tlx = pss->brx - pdev->x_range.quant;
+            }
             pss->predef_window = pdw_none;
             if (i)
                 *i = SANE_INFO_RELOAD_PARAMS;
             break;
         case OPT_BRY:
             pss->bry = *(SANE_Fixed *) v;
+            if (fabs(pss->bry - pdev->y_range.min) < pdev->y_range.quant) {
+                pss->bry += pdev->y_range.quant;
+            }
+            if (pss->bry < pss->tly) {
+                pss->tly = pss->bry - pdev->y_range.quant;
+            }
             pss->predef_window = pdw_none;
             if (i)
                 *i = SANE_INFO_RELOAD_PARAMS;
@@ -2353,7 +2357,7 @@ SANE_Status sane_control_option (SANE_Handle h,
                 *i = 0;
             break;
         case OPT_NEGATIVE:
-            pss->halftone = DEFAULT_NEGATIVE;
+            pss->negative = DEFAULT_NEGATIVE;
             if (i)
                 *i = 0;
             break;
@@ -2694,7 +2698,7 @@ static SANE_Status download_gamma_tables (SnapScan_Scanner *pss)
                                  pss->buf + SEND_LENGTH);
                 status = send (pss, DTC_GAMMA, dtcq_gamma_green);
                 CHECK_STATUS (status, me, "send");
-                
+
                 gamma_from_sane (pss->gamma_length, pss->gamma_table_b,
                                  pss->buf + SEND_LENGTH);
                 status = send (pss, DTC_GAMMA, dtcq_gamma_blue);
@@ -2732,7 +2736,7 @@ static SANE_Status download_gamma_tables (SnapScan_Scanner *pss)
                          pss->buf + SEND_LENGTH, bpp);
                 status = send (pss, DTC_GAMMA, dtcq_gamma_green);
                 CHECK_STATUS (status, me, "send");
-                
+
                 gamma_n (gamma_b, pss->bright, pss->contrast,
                          pss->buf + SEND_LENGTH, bpp);
                 status = send (pss, DTC_GAMMA, dtcq_gamma_blue);
@@ -2764,7 +2768,8 @@ static SANE_Status download_halftone_matrices (SnapScan_Scanner *pss)
 {
     static char me[] = "download_halftone_matrices";
     SANE_Status status = SANE_STATUS_GOOD;
-    if (pss->halftone)
+    if ((pss->halftone) &&
+        ((actual_mode(pss) == MD_LINEART) || (actual_mode(pss) == MD_BILEVELCOLOUR)))
     {
         u_char *matrix;
         size_t matrix_sz;
@@ -3123,15 +3128,41 @@ SANE_Status sane_get_select_fd (SANE_Handle h, SANE_Int * fd)
 
 /*
  * $Log$
- * Revision 1.10  2001/10/27 09:08:14  oliverschwartz
- * Check USB vendor IDs to avoid hanging scanners, fix bug in dither matrix computation
+ * Revision 1.11  2001/12/17 22:51:51  oliverschwartz
+ * Update to snapscan-20011212 (snapscan 1.4.3)
  *
- * Revision 1.9  2001/10/25 10:56:39  oliverschwartz
+ * Revision 1.33  2001/12/12 19:43:30  oliverschwartz
+ * - Set version number to 1.4.3
+ * - Clean up CVS Log
+ *
+ * Revision 1.32  2001/12/09 23:06:45  oliverschwartz
+ * - use sense handler for USB if scanner reports CHECK_CONDITION
+ *
+ * Revision 1.31  2001/12/08 11:50:34  oliverschwartz
+ * Fix dither matrix computation
+ *
+ * Revision 1.30  2001/11/29 22:50:14  oliverschwartz
+ * Add support for SnapScan e52
+ *
+ * Revision 1.29  2001/11/27 23:16:17  oliverschwartz
+ * - Fix color alignment for SnapScan 600
+ * - Added documentation in snapscan-sources.c
+ * - Guard against TL_X < BR_X and TL_Y < BR_Y
+ *
+ * Revision 1.28  2001/11/25 18:51:41  oliverschwartz
+ * added support for SnapScan e52 thanks to Rui Lopes
+ *
+ * Revision 1.27  2001/11/16 20:28:35  oliverschwartz
+ * add support for Snapscan e26
+ *
+ * Revision 1.26  2001/11/16 20:23:16  oliverschwartz
+ * Merge with sane-1.0.6
+ *   - Check USB vendor IDs to avoid hanging scanners
+ *   - fix bug in dither matrix computation
+ *
+ * Revision 1.25  2001/10/25 11:06:22  oliverschwartz
  * Change snapscan backend version number to 1.4.0
  *
- * Revision 1.8  2001/10/12 21:19:14  oliverschwartz
- * update to snapscan-20011012
- *
  * Revision 1.24  2001/10/11 14:02:10  oliverschwartz
  * Distinguish between e20/e25 and e40/e50
  *
diff --git a/backend/snapscan.desc b/backend/snapscan.desc
index d110fb7c1..84ab72cb1 100644
--- a/backend/snapscan.desc
+++ b/backend/snapscan.desc
@@ -56,6 +56,10 @@
 :interface "USB"
 :comment "Have no specific programming info yet."
 
+:model "SnapScan e26"
+:interface "USB"
+:comment "Have no specific programming info yet."
+
 :model "SnapScan e40"
 :interface "USB"
 :comment "Have no specific programming info yet."
@@ -64,6 +68,10 @@
 :interface "USB"
 :comment "Have no specific programming info yet."
 
+:model "SnapScan e52"
+:interface "USB"
+:comment "Have no specific programming info yet."
+
 :model "SnapScan e60"
 :interface "USB"
 :comment "Have no specific programming info yet."
diff --git a/backend/snapscan.h b/backend/snapscan.h
index 55c381c15..ed3d341a9 100644
--- a/backend/snapscan.h
+++ b/backend/snapscan.h
@@ -84,6 +84,7 @@ typedef enum
     SNAPSCAN1212U,
     SNAPSCANE20,        /* SnapScan e20/e25, 600 DPI */
     SNAPSCANE50,        /* SnapScan e40/e50, 1200 DPI */
+    SNAPSCANE52,        /* SnapScan e52, 1200 DPI, no quality calibration */
     ACER300F,
     VUEGO310S,          /* Vuego-Version of SnapScan 310 WG changed */
     VUEGO610S,          /* Vuego 610S and 610plus SJU changed */
@@ -120,8 +121,11 @@ static struct SnapScan_Model_desc scanners[] =
     {"SNAPSCAN 1212U_2",    SNAPSCAN1212U},
     {"SNAPSCAN e20",        SNAPSCANE20},
     {"SNAPSCAN e25",        SNAPSCANE20},
+    {"SNAPSCAN e26",        SNAPSCANE20},
+    {"SNAPSCAN e26    ",        SNAPSCANE20},
     {"SNAPSCAN e40",        SNAPSCANE50},
     {"SNAPSCAN e50",        SNAPSCANE50},
+    {"SNAPSCAN e52",        SNAPSCANE52},
     {"SNAPSCAN 1236",       SNAPSCAN1236},
     {"SNAPSCAN 1236U",      SNAPSCAN1236},
     {"SNAPSCAN 300",        SNAPSCAN300},
@@ -321,11 +325,25 @@ struct snapscan_scanner
 
 /*
  * $Log$
- * Revision 1.7  2001/10/27 09:08:17  oliverschwartz
- * Check USB vendor IDs to avoid hanging scanners, fix bug in dither matrix computation
+ * Revision 1.8  2001/12/17 22:51:52  oliverschwartz
+ * Update to snapscan-20011212 (snapscan 1.4.3)
  *
- * Revision 1.6  2001/10/12 21:19:16  oliverschwartz
- * update to snapscan-20011012
+ * Revision 1.24  2001/12/12 19:44:59  oliverschwartz
+ * Clean up CVS log
+ *
+ * Revision 1.23  2001/11/25 18:51:41  oliverschwartz
+ * added support for SnapScan e52 thanks to Rui Lopes
+ *
+ * Revision 1.22  2001/11/16 20:56:47  oliverschwartz
+ * additional identification string for e26 added
+ *
+ * Revision 1.21  2001/11/16 20:28:35  oliverschwartz
+ * add support for Snapscan e26
+ *
+ * Revision 1.20  2001/11/16 20:23:16  oliverschwartz
+ * Merge with sane-1.0.6
+ *   - Check USB vendor IDs to avoid hanging scanners
+ *   - fix bug in dither matrix computation
  *
  * Revision 1.19  2001/10/11 14:02:10  oliverschwartz
  * Distinguish between e20/e25 and e40/e50
@@ -369,15 +387,6 @@ struct snapscan_scanner
  * Applying Mikael Magnusson patch concerning Gamma correction
  * Support for 1212U_2
  *
- * Revision 1.3  2001/03/04 16:51:29  mikael
- * Added Scan Mode, Geometry, Enhancement and Advanced groups. Added Quality Calibration, Analog Gamma Bind, Custom Gamma and Gamma Vector GS,R,G,B options. Added SNAPSCAN 1212U_2.
- *
- * Revision 1.2  2001/02/16 18:32:28  mikael
- * impl calibration, signed position, increased buffer size
- *
- * Revision 1.1.1.1  2001/02/10 17:09:29  mikael
- * Imported from snapscan-11282000.tar.gz
- *
  * Revision 1.8  2000/11/10 01:01:59  sable
  * USB (kind of) autodetection
  *