# Original patch by Jim Studt on Linux-uvc-devel
diff -ur trunk.232/uvc_v4l2.c trunk.232.JPEGCOMP/uvc_v4l2.c
--- trunk.232/uvc_v4l2.c	2008-07-18 22:12:57.000000000 +0200
+++ trunk.232.JPEGCOMP/uvc_v4l2.c	2008-07-18 22:24:14.000000000 +0200
@@ -332,6 +332,45 @@
 	return 0;
 }
 
+
+static int uvc_v4l2_get_jpegcompression(struct uvc_video_device *video,
+               struct v4l2_jpegcompression *parm)
+{
+       memset(parm, 0, sizeof *parm);
+       parm->quality = video->streaming->ctrl.wCompQuality/100;  /* scale  from UVC 10000 to familiar 10 */
+       // Are DQT and DRI required in UVC? Maybe we should turn on their  bits in jpeg_markers?
+
+       return 0;
+}
+
+static int uvc_v4l2_set_jpegcompression(struct uvc_video_device *video,
+               struct v4l2_jpegcompression *parm)
+{
+       struct uvc_streaming_control probe;
+       int ret;
+       int quality;
+
+       memcpy(&probe, &video->streaming->ctrl, sizeof probe);
+       quality = parm->quality * 100; /* scale from famliar 100 to UVC  10000 */
+
+       uvc_trace(UVC_TRACE_FORMAT, "Setting jpeg quality to %d.\n", quality);
+
+       probe.wCompQuality = quality;
+       /* Probe the device with the new settings. */
+       if ((ret = uvc_probe_video(video, &probe)) < 0)
+               return ret;
+
+       /* Commit the new settings. */
+       if ((ret = uvc_set_video_ctrl(video, &probe, 0)) < 0)
+               return ret;
+
+       memcpy(&video->streaming->ctrl, &probe, sizeof probe);
+
+       return 0;
+}
+
+
+
 /* ------------------------------------------------------------------------
  * Privilege management
  */
@@ -793,6 +832,16 @@
 		break;
 	}
 
+       case VIDIOC_G_JPEGCOMP:
+               return uvc_v4l2_get_jpegcompression(video, (struct  v4l2_jpegcompression*)arg);
+
+       case VIDIOC_S_JPEGCOMP:
+               if ((ret = uvc_acquire_privileges(handle)) < 0)
+                       return ret;
+
+               return uvc_v4l2_set_jpegcompression(video, (struct  v4l2_jpegcompression*)arg);
+
+
 	/* Get & Set streaming parameters */
 	case VIDIOC_G_PARM:
 		return uvc_v4l2_get_streamparm(video, arg);
diff -ur trunk.232/uvc_video.c trunk.232.JPEGCOMP/uvc_video.c
--- trunk.232/uvc_video.c	2008-07-18 22:12:57.000000000 +0200
+++ trunk.232.JPEGCOMP/uvc_video.c	2008-07-18 22:35:17.000000000 +0200
@@ -185,7 +185,7 @@
 int uvc_probe_video(struct uvc_video_device *video,
 	struct uvc_streaming_control *probe)
 {
-	struct uvc_streaming_control probe_min, probe_max;
+	struct uvc_streaming_control probe_min, probe_max, probe_res;
 	__u16 bandwidth;
 	unsigned int i;
 	int ret;
@@ -207,11 +207,39 @@
 		ret = uvc_get_video_ctrl(video, &probe_min, 1, GET_MIN);
 		if (ret < 0)
 			goto done;
-		ret = uvc_get_video_ctrl(video, &probe_max, 1, GET_MAX);
+
+		/* ret = uvc_get_video_ctrl(video, &probe_max, 1, GET_MAX); */
+
+                ret = uvc_get_video_ctrl(video, &probe_max, 1, GET_MAX);
+		if (ret < 0)
+			goto done;
+
+		ret = uvc_get_video_ctrl(video, &probe_res, 1, GET_RES);
 		if (ret < 0)
 			goto done;
 
-		probe->wCompQuality = probe_max.wCompQuality;
+
+               /* pin wCompQuality to the legal range */
+               if ( probe->wCompQuality < probe_min.wCompQuality) probe->wCompQuality = probe_min.wCompQuality;
+               else if ( probe->wCompQuality > probe_max.wCompQuality) probe->wCompQuality = probe_max.wCompQuality;
+               else {
+                   int range, steps, step_size;
+/*		probe->wCompQuality = probe_max.wCompQuality;   */
+                   /* this mess of code makes sure wCompQuality lands on one of  the legal values */
+                   step_size = probe_res.wCompQuality;
+                   range = probe_max.wCompQuality - probe_min.wCompQuality;
+                   if ( range != 0 && step_size != 0) {
+                       steps = range / step_size;
+                       probe->wCompQuality = probe_min.wCompQuality +
+                           (probe->wCompQuality - probe_min.wCompQuality + step_size/2) *steps/range*step_size;
+                   } else {
+                       probe->wCompQuality = probe_max.wCompQuality;
+                   }
+               }
+
+
+
+
 	}
 
 	for (i = 0; i < 2; ++i) {
@@ -234,7 +262,8 @@
 		/* TODO: negotiate compression parameters */
 		probe->wKeyFrameRate = probe_min.wKeyFrameRate;
 		probe->wPFrameRate = probe_min.wPFrameRate;
-		probe->wCompQuality = probe_max.wCompQuality;
+		//probe->wCompQuality = probe_max.wCompQuality;
+		probe->wCompQuality = probe_min.wCompQuality;
 		probe->wCompWindowSize = probe_min.wCompWindowSize;
 	}