diff --git a/include/darknet.h b/include/darknet.h
index 25e702b2..552cad78 100644
--- a/include/darknet.h
+++ b/include/darknet.h
@@ -600,6 +600,7 @@ typedef struct network {
     int flip; // horizontal flip 50% probability augmentaiont for classifier training (default = 1)
     int blur;
     int mixup;
+    int letter_box;
     float angle;
     float aspect;
     float exposure;
@@ -760,6 +761,7 @@ typedef struct load_args {
     int mini_batch;
     int track;
     int augment_speed;
+    int letter_box;
     int show_imgs;
     float jitter;
     int flip;
@@ -827,7 +829,7 @@ LIB_API layer* get_network_layer(network* net, int i);
 LIB_API detection *make_network_boxes(network *net, float thresh, int *num);
 LIB_API void reset_rnn(network *net);
 LIB_API float *network_predict_image(network *net, image im);
-LIB_API float validate_detector_map(char *datacfg, char *cfgfile, char *weightfile, float thresh_calc_avg_iou, const float iou_thresh, const int map_points, network *existing_net);
+LIB_API float validate_detector_map(char *datacfg, char *cfgfile, char *weightfile, float thresh_calc_avg_iou, const float iou_thresh, const int map_points, int letter_box, network *existing_net);
 LIB_API void train_detector(char *datacfg, char *cfgfile, char *weightfile, int *gpus, int ngpus, int clear, int dont_show, int calc_map, int mjpeg_port, int show_imgs);
 LIB_API void test_detector(char *datacfg, char *cfgfile, char *weightfile, char *filename, float thresh,
     float hier_thresh, int dont_show, int ext_output, int save_labels, char *outfile, int letter_box);
diff --git a/src/data.c b/src/data.c
index 3858d427..571bfd01 100644
--- a/src/data.c
+++ b/src/data.c
@@ -804,8 +804,8 @@ void blend_truth(float *new_truth, int boxes, float *old_truth)
 
 #include "http_stream.h"
 
-data load_data_detection(int n, char **paths, int m, int w, int h, int c, int boxes, int classes, int use_flip, int use_blur, int use_mixup, float jitter,
-    float hue, float saturation, float exposure, int mini_batch, int track, int augment_speed, int show_imgs)
+data load_data_detection(int n, char **paths, int m, int w, int h, int c, int boxes, int classes, int use_flip, int use_blur, int use_mixup,
+    float jitter, float hue, float saturation, float exposure, int mini_batch, int track, int augment_speed, int letter_box, int show_imgs)
 {
     const int random_index = random_gen();
     c = c ? c : 3;
@@ -828,7 +828,7 @@ data load_data_detection(int n, char **paths, int m, int w, int h, int c, int bo
     d.X.vals = (float**)calloc(d.X.rows, sizeof(float*));
     d.X.cols = h*w*c;
 
-    float r1 = 0, r2 = 0, r3 = 0, r4 = 0;
+    float r1 = 0, r2 = 0, r3 = 0, r4 = 0, r_scale = 0;
     float dhue = 0, dsat = 0, dexp = 0, flip = 0, blur = 0;
     int augmentation_calculated = 0;
 
@@ -862,6 +862,8 @@ data load_data_detection(int n, char **paths, int m, int w, int h, int c, int bo
                 r3 = random_float();
                 r4 = random_float();
 
+                r_scale = random_float();
+
                 dhue = rand_uniform_strong(-hue, hue);
                 dsat = rand_scale(saturation);
                 dexp = rand_scale(exposure);
@@ -874,6 +876,33 @@ data load_data_detection(int n, char **paths, int m, int w, int h, int c, int bo
             int pright = rand_precalc_random(-dw, dw, r2);
             int ptop = rand_precalc_random(-dh, dh, r3);
             int pbot = rand_precalc_random(-dh, dh, r4);
+            //printf("\n pleft = %d, pright = %d, ptop = %d, pbot = %d, ow = %d, oh = %d \n", pleft, pright, ptop, pbot, ow, oh);
+
+            float scale = rand_precalc_random(.25, 2, r_scale); // unused currently
+
+            if (letter_box)
+            {
+                float img_ar = (float)ow / (float)oh;
+                float net_ar = (float)w / (float)h;
+                float result_ar = img_ar / net_ar;
+                //printf(" ow = %d, oh = %d, w = %d, h = %d, img_ar = %f, net_ar = %f, result_ar = %f \n", ow, oh, w, h, img_ar, net_ar, result_ar);
+                if (result_ar > 1)  // sheight - should be increased
+                {
+                    float oh_tmp = ow / net_ar;
+                    float delta_h = (oh_tmp - oh)/2;
+                    ptop = ptop - delta_h;
+                    pbot = pbot - delta_h;
+                    //printf(" result_ar = %f, oh_tmp = %f, delta_h = %d, ptop = %f, pbot = %f \n", result_ar, oh_tmp, delta_h, ptop, pbot);
+                }
+                else  // swidth - should be increased
+                {
+                    float ow_tmp = oh * net_ar;
+                    float delta_w = (ow_tmp - ow)/2;
+                    pleft = pleft - delta_w;
+                    pright = pright - delta_w;
+                    //printf(" result_ar = %f, ow_tmp = %f, delta_w = %d, pleft = %f, pright = %f \n", result_ar, ow_tmp, delta_w, pleft, pright);
+                }
+            }
 
             int swidth = ow - pleft - pright;
             int sheight = oh - ptop - pbot;
@@ -884,9 +913,10 @@ data load_data_detection(int n, char **paths, int m, int w, int h, int c, int bo
             float dx = ((float)pleft / ow) / sx;
             float dy = ((float)ptop / oh) / sy;
 
+
             fill_truth_detection(filename, boxes, truth, classes, flip, dx, dy, 1. / sx, 1. / sy, w, h);
 
-            image ai = image_data_augmentation(src, w, h, pleft, ptop, swidth, sheight, flip, jitter, dhue, dsat, dexp,
+            image ai = image_data_augmentation(src, w, h, pleft, ptop, swidth, sheight, flip, dhue, dsat, dexp,
                 blur, boxes, d.y.vals[i]);
 
             if (i_mixup) {
@@ -947,7 +977,7 @@ void blend_images(image new_img, float alpha, image old_img, float beta)
 }
 
 data load_data_detection(int n, char **paths, int m, int w, int h, int c, int boxes, int classes, int use_flip, int use_blur, int use_mixup, float jitter,
-    float hue, float saturation, float exposure, int mini_batch, int track, int augment_speed, int show_imgs)
+    float hue, float saturation, float exposure, int mini_batch, int track, int augment_speed, int letter_box, int show_imgs)
 {
     const int random_index = random_gen();
     c = c ? c : 3;
@@ -971,7 +1001,7 @@ data load_data_detection(int n, char **paths, int m, int w, int h, int c, int bo
     d.X.vals = (float**)calloc(d.X.rows, sizeof(float*));
     d.X.cols = h*w*c;
 
-    float r1 = 0, r2 = 0, r3 = 0, r4 = 0;
+    float r1 = 0, r2 = 0, r3 = 0, r4 = 0, r_scale;
     float dhue = 0, dsat = 0, dexp = 0, flip = 0;
     int augmentation_calculated = 0;
 
@@ -999,6 +1029,8 @@ data load_data_detection(int n, char **paths, int m, int w, int h, int c, int bo
                 r3 = random_float();
                 r4 = random_float();
 
+                r_scale = random_float();
+
                 dhue = rand_uniform_strong(-hue, hue);
                 dsat = rand_scale(saturation);
                 dexp = rand_scale(exposure);
@@ -1011,6 +1043,32 @@ data load_data_detection(int n, char **paths, int m, int w, int h, int c, int bo
             int ptop = rand_precalc_random(-dh, dh, r3);
             int pbot = rand_precalc_random(-dh, dh, r4);
 
+            float scale = rand_precalc_random(.25, 2, r_scale); // unused currently
+
+            if (letter_box)
+            {
+                float img_ar = (float)ow / (float)oh;
+                float net_ar = (float)w / (float)h;
+                float result_ar = img_ar / net_ar;
+                //printf(" ow = %d, oh = %d, w = %d, h = %d, img_ar = %f, net_ar = %f, result_ar = %f \n", ow, oh, w, h, img_ar, net_ar, result_ar);
+                if (result_ar > 1)  // sheight - should be increased
+                {
+                    float oh_tmp = ow / net_ar;
+                    float delta_h = (oh_tmp - oh) / 2;
+                    ptop = ptop - delta_h;
+                    pbot = pbot - delta_h;
+                    //printf(" result_ar = %f, oh_tmp = %f, delta_h = %d, ptop = %f, pbot = %f \n", result_ar, oh_tmp, delta_h, ptop, pbot);
+                }
+                else  // swidth - should be increased
+                {
+                    float ow_tmp = oh * net_ar;
+                    float delta_w = (ow_tmp - ow) / 2;
+                    pleft = pleft - delta_w;
+                    pright = pright - delta_w;
+                    //printf(" result_ar = %f, ow_tmp = %f, delta_w = %d, pleft = %f, pright = %f \n", result_ar, ow_tmp, delta_w, pleft, pright);
+                }
+            }
+
             int swidth = ow - pleft - pright;
             int sheight = oh - ptop - pbot;
 
@@ -1100,7 +1158,7 @@ void *load_thread(void *ptr)
         *a.d = load_data_region(a.n, a.paths, a.m, a.w, a.h, a.num_boxes, a.classes, a.jitter, a.hue, a.saturation, a.exposure);
     } else if (a.type == DETECTION_DATA){
         *a.d = load_data_detection(a.n, a.paths, a.m, a.w, a.h, a.c, a.num_boxes, a.classes, a.flip, a.blur, a.mixup, a.jitter,
-            a.hue, a.saturation, a.exposure, a.mini_batch, a.track, a.augment_speed, a.show_imgs);
+            a.hue, a.saturation, a.exposure, a.mini_batch, a.track, a.augment_speed, a.letter_box, a.show_imgs);
     } else if (a.type == SWAG_DATA){
         *a.d = load_data_swag(a.paths, a.n, a.classes, a.jitter);
     } else if (a.type == COMPARE_DATA){
diff --git a/src/data.h b/src/data.h
index b99b4e9a..17edc5cf 100644
--- a/src/data.h
+++ b/src/data.h
@@ -86,8 +86,8 @@ void print_letters(float *pred, int n);
 data load_data_captcha(char **paths, int n, int m, int k, int w, int h);
 data load_data_captcha_encode(char **paths, int n, int m, int w, int h);
 data load_data_old(char **paths, int n, int m, char **labels, int k, int w, int h);
-data load_data_detection(int n, char **paths, int m, int w, int h, int c, int boxes, int classes, int use_flip, int use_blur, int use_mixup, float jitter,
-    float hue, float saturation, float exposure, int mini_batch, int track, int augment_speed, int show_imgs);
+data load_data_detection(int n, char **paths, int m, int w, int h, int c, int boxes, int classes, int use_flip, int use_blur, int use_mixup,
+    float jitter, float hue, float saturation, float exposure, int mini_batch, int track, int augment_speed, int letter_box, int show_imgs);
 data load_data_tag(char **paths, int n, int m, int k, int use_flip, int min, int max, int size, float angle, float aspect, float hue, float saturation, float exposure);
 matrix load_image_augment_paths(char **paths, int n, int use_flip, int min, int max, int size, float angle, float aspect, float hue, float saturation, float exposure);
 data load_data_super(char **paths, int n, int m, int w, int h, int scale);
diff --git a/src/detector.c b/src/detector.c
index 074365fb..9f77ea5a 100644
--- a/src/detector.c
+++ b/src/detector.c
@@ -133,6 +133,7 @@ void train_detector(char *datacfg, char *cfgfile, char *weightfile, int *gpus, i
     args.exposure = net.exposure;
     args.saturation = net.saturation;
     args.hue = net.hue;
+    args.letter_box = net.letter_box;
     if (dont_show && show_imgs) show_imgs = 2;
     args.show_imgs = show_imgs;
 
@@ -275,7 +276,7 @@ void train_detector(char *datacfg, char *cfgfile, char *weightfile, int *gpus, i
             //network net_combined = combine_train_valid_networks(net, net_map);
 
             iter_map = i;
-            mean_average_precision = validate_detector_map(datacfg, cfgfile, weightfile, 0.25, 0.5, 0, &net_map);// &net_combined);
+            mean_average_precision = validate_detector_map(datacfg, cfgfile, weightfile, 0.25, 0.5, 0, net.letter_box, &net_map);// &net_combined);
             printf("\n mean_average_precision (mAP@0.5) = %f \n", mean_average_precision);
             if (mean_average_precision > best_map) {
                 best_map = mean_average_precision;
@@ -660,7 +661,7 @@ int detections_comparator(const void *pa, const void *pb)
     return 0;
 }
 
-float validate_detector_map(char *datacfg, char *cfgfile, char *weightfile, float thresh_calc_avg_iou, const float iou_thresh, const int map_points, network *existing_net)
+float validate_detector_map(char *datacfg, char *cfgfile, char *weightfile, float thresh_calc_avg_iou, const float iou_thresh, const int map_points, int letter_box, network *existing_net)
 {
     int j;
     list *options = read_data_cfg(datacfg);
@@ -733,8 +734,8 @@ float validate_detector_map(char *datacfg, char *cfgfile, char *weightfile, floa
     args.w = net.w;
     args.h = net.h;
     args.c = net.c;
-    args.type = IMAGE_DATA;
-    //args.type = LETTERBOX_DATA;
+    if (letter_box) args.type = LETTERBOX_DATA;
+    else args.type = IMAGE_DATA;
 
     //const float thresh_calc_avg_iou = 0.24;
     float avg_iou = 0;
@@ -783,14 +784,12 @@ float validate_detector_map(char *datacfg, char *cfgfile, char *weightfile, floa
             float hier_thresh = 0;
             detection *dets;
             if (args.type == LETTERBOX_DATA) {
-                int letterbox = 1;
-                dets = get_network_boxes(&net, val[t].w, val[t].h, thresh, hier_thresh, 0, 1, &nboxes, letterbox);
+                dets = get_network_boxes(&net, val[t].w, val[t].h, thresh, hier_thresh, 0, 1, &nboxes, letter_box);
             }
             else {
-                int letterbox = 0;
-                dets = get_network_boxes(&net, 1, 1, thresh, hier_thresh, 0, 0, &nboxes, letterbox);
+                dets = get_network_boxes(&net, 1, 1, thresh, hier_thresh, 0, 0, &nboxes, letter_box);
             }
-            //detection *dets = get_network_boxes(&net, val[t].w, val[t].h, thresh, hier_thresh, 0, 1, &nboxes, letterbox); // for letterbox=1
+            //detection *dets = get_network_boxes(&net, val[t].w, val[t].h, thresh, hier_thresh, 0, 1, &nboxes, letter_box); // for letter_box=1
             if (nms) do_nms_sort(dets, nboxes, l.classes, nms);
 
             char labelpath[4096];
@@ -1486,7 +1485,7 @@ void run_detector(int argc, char **argv)
     else if (0 == strcmp(argv[2], "train")) train_detector(datacfg, cfg, weights, gpus, ngpus, clear, dont_show, calc_map, mjpeg_port, show_imgs);
     else if (0 == strcmp(argv[2], "valid")) validate_detector(datacfg, cfg, weights, outfile);
     else if (0 == strcmp(argv[2], "recall")) validate_detector_recall(datacfg, cfg, weights);
-    else if (0 == strcmp(argv[2], "map")) validate_detector_map(datacfg, cfg, weights, thresh, iou_thresh, map_points, NULL);
+    else if (0 == strcmp(argv[2], "map")) validate_detector_map(datacfg, cfg, weights, thresh, iou_thresh, map_points, letter_box, NULL);
     else if (0 == strcmp(argv[2], "calc_anchors")) calc_anchors(datacfg, num_of_clusters, width, height, show);
     else if (0 == strcmp(argv[2], "demo")) {
         list *options = read_data_cfg(datacfg);
diff --git a/src/image_opencv.cpp b/src/image_opencv.cpp
index b60f03cb..91d07bd7 100644
--- a/src/image_opencv.cpp
+++ b/src/image_opencv.cpp
@@ -1137,7 +1137,7 @@ static box float_to_box_stride(float *f, int stride)
 
 image image_data_augmentation(mat_cv* mat, int w, int h,
     int pleft, int ptop, int swidth, int sheight, int flip,
-    float jitter, float dhue, float dsat, float dexp,
+    float dhue, float dsat, float dexp,
     int blur, int num_boxes, float *truth)
 {
     image out;
diff --git a/src/image_opencv.h b/src/image_opencv.h
index 2af5f24e..860f27e8 100644
--- a/src/image_opencv.h
+++ b/src/image_opencv.h
@@ -95,7 +95,7 @@ void draw_train_loss(mat_cv* img, int img_size, float avg_loss, float max_img_lo
 // Data augmentation
 image image_data_augmentation(mat_cv* mat, int w, int h,
     int pleft, int ptop, int swidth, int sheight, int flip,
-    float jitter, float dhue, float dsat, float dexp,
+    float dhue, float dsat, float dexp,
     int blur, int num_boxes, float *truth);
 
 // blend two images with (alpha and beta)
diff --git a/src/network.h b/src/network.h
index 186fe3d8..2bee2cb2 100644
--- a/src/network.h
+++ b/src/network.h
@@ -153,7 +153,7 @@ float get_network_cost(network net);
 //LIB_API network *load_network_custom(char *cfg, char *weights, int clear, int batch);
 //LIB_API network *load_network(char *cfg, char *weights, int clear);
 //LIB_API float *network_predict_image(network *net, image im);
-//LIB_API float validate_detector_map(char *datacfg, char *cfgfile, char *weightfile, float thresh_calc_avg_iou, const float iou_thresh, network *existing_net);
+//LIB_API float validate_detector_map(char *datacfg, char *cfgfile, char *weightfile, float thresh_calc_avg_iou, const float iou_thresh, int map_points, int letter_box, network *existing_net);
 //LIB_API void train_detector(char *datacfg, char *cfgfile, char *weightfile, int *gpus, int ngpus, int clear, int dont_show, int calc_map, int mjpeg_port);
 //LIB_API int network_width(network *net);
 //LIB_API int network_height(network *net);
diff --git a/src/parser.c b/src/parser.c
index d45f625c..5f6658e6 100644
--- a/src/parser.c
+++ b/src/parser.c
@@ -738,6 +738,7 @@ void parse_net_options(list *options, network *net)
     net->flip = option_find_int_quiet(options, "flip", 1);
     net->blur = option_find_int_quiet(options, "blur", 0);
     net->mixup = option_find_int_quiet(options, "mixup", 0);
+    net->letter_box = option_find_int_quiet(options, "letter_box", 0);
 
     net->angle = option_find_float_quiet(options, "angle", 0);
     net->aspect = option_find_float_quiet(options, "aspect", 1);