diff --git a/common/image_u8x4.c b/common/image_u8x4.c
new file mode 100644
index 0000000..3520537
--- /dev/null
+++ b/common/image_u8x4.c
@@ -0,0 +1,233 @@
+/* Copyright (C) 2013-2016, The Regents of The University of Michigan.
+All rights reserved.
+This software was developed in the APRIL Robotics Lab under the
+direction of Edwin Olson, ebolson@umich.edu. This software may be
+available under alternative licensing terms; contact the address above.
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+1. Redistributions of source code must retain the above copyright notice, this
+   list of conditions and the following disclaimer.
+2. Redistributions in binary form must reproduce the above copyright notice,
+   this list of conditions and the following disclaimer in the documentation
+   and/or other materials provided with the distribution.
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
+ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+The views and conclusions contained in the software and documentation are those
+of the authors and should not be interpreted as representing official policies,
+either expressed or implied, of the Regents of The University of Michigan.
+*/
+
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "pam.h"
+#include "pnm.h"
+#include "image_u8x4.h"
+
+// least common multiple of 64 (sandy bridge cache line) and 64 (stride needed
+// for 16byte-wide RGBA processing).
+#define DEFAULT_ALIGNMENT_U8X4 64
+
+image_u8x4_t *image_u8x4_create(unsigned int width, unsigned int height)
+{
+    return image_u8x4_create_alignment(width, height, DEFAULT_ALIGNMENT_U8X4);
+}
+
+image_u8x4_t *image_u8x4_create_alignment(unsigned int width, unsigned int height, unsigned int alignment)
+{
+    int stride = 4*width;
+
+    if ((stride % alignment) != 0)
+        stride += alignment - (stride % alignment);
+
+    uint8_t *buf = calloc(height*stride, sizeof(uint8_t));
+
+    // const initializer
+    image_u8x4_t tmp = { .width = width, .height = height, .stride = stride, .buf = buf };
+
+    image_u8x4_t *im = calloc(1, sizeof(image_u8x4_t));
+    memcpy(im, &tmp, sizeof(image_u8x4_t));
+    return im;
+}
+
+image_u8x4_t *image_u8x4_copy(const image_u8x4_t *in)
+{
+    uint8_t *buf = malloc(in->height*in->stride*sizeof(uint8_t));
+    memcpy(buf, in->buf, in->height*in->stride*sizeof(uint8_t));
+
+    // const initializer
+    image_u8x4_t tmp = { .width = in->width, .height = in->height, .stride = in->stride, .buf = buf };
+
+    image_u8x4_t *copy = calloc(1, sizeof(image_u8x4_t));
+    memcpy(copy, &tmp, sizeof(image_u8x4_t));
+    return copy;
+}
+
+void image_u8x4_destroy(image_u8x4_t *im)
+{
+    if (!im)
+        return;
+
+    free(im->buf);
+    free(im);
+}
+
+////////////////////////////////////////////////////////////
+image_u8x4_t *image_u8x4_create_from_pam(const char *inpath)
+{
+    pam_t *pam = pam_create_from_file(inpath);
+    if (!pam)
+        return NULL;
+
+    image_u8x4_t *im = image_u8x4_create(pam->width, pam->height);
+
+    for (int y = 0; y < pam->height; y++) {
+        if (pam->depth == 1) {
+            for (int x = 0; x < pam->width; x++) {
+                im->buf[y*im->stride + 4*x + 0] = pam->data[pam->width*y + x + 0];
+                im->buf[y*im->stride + 4*x + 1] = pam->data[pam->width*y + x + 0];
+                im->buf[y*im->stride + 4*x + 2] = pam->data[pam->width*y + x + 0];
+                im->buf[y*im->stride + 4*x + 3] = 255;
+            }
+        } else if (pam->depth == 3) {
+            for (int x = 0; x < pam->width; x++) {
+                im->buf[y*im->stride + 4*x + 0] = pam->data[3*pam->width*y + 3*x + 0];
+                im->buf[y*im->stride + 4*x + 1] = pam->data[3*pam->width*y + 3*x + 1];
+                im->buf[y*im->stride + 4*x + 2] = pam->data[3*pam->width*y + 3*x + 2];
+                im->buf[y*im->stride + 4*x + 3] = 255;
+            }
+        } else if (pam->depth == 4) {
+            memcpy(&im->buf[y*im->stride], &pam->data[4*pam->width*y], 4*pam->width);
+        } else {
+            assert(0); // not implemented
+        }
+    }
+
+    pam_destroy(pam);
+    return im;
+}
+////////////////////////////////////////////////////////////
+// PNM file i/o
+
+// Create an RGBA image from PNM
+image_u8x4_t *image_u8x4_create_from_pnm(const char *path)
+{
+    pnm_t *pnmp = pnm_create_from_file(path);
+    if (pnmp == NULL)
+        return NULL;
+
+    pnm_t pnm = *pnmp;
+    image_u8x4_t *imp = NULL;
+
+    switch (pnm.format) {
+        case PNM_FORMAT_GRAY: {
+            imp = image_u8x4_create(pnm.width, pnm.height);
+
+            // copy struct by value for common subexpression elimination
+            const image_u8x4_t im = *imp;
+
+            for (int y = 0; y < im.height; y++) {
+                for (int x = 0; x < im.width; x++) {
+                    uint8_t gray = pnm.buf[y*pnm.width + x];
+                    im.buf[y*im.stride + 4*x + 0] = gray;
+                    im.buf[y*im.stride + 4*x + 1] = gray;
+                    im.buf[y*im.stride + 4*x + 2] = gray;
+                    im.buf[y*im.stride + 4*x + 3] = 0xff;
+                }
+            }
+
+            break;
+        }
+
+        case PNM_FORMAT_RGB: {
+            imp = image_u8x4_create(pnm.width, pnm.height);
+
+            // copy struct by value for common subexpression elimination
+            const image_u8x4_t im = *imp;
+
+            // Gray conversion for RGB is gray = (r + g + g + b)/4
+            for (int y = 0; y < im.height; y++) {
+                for (int x = 0; x < im.width; x++) {
+
+                    uint8_t r = pnm.buf[y*pnm.width*3 + 3*x + 0];
+                    uint8_t g = pnm.buf[y*pnm.width*3 + 3*x + 1];
+                    uint8_t b = pnm.buf[y*pnm.width*3 + 3*x + 2];
+
+                    im.buf[y*im.stride + 4*x + 0] = r;
+                    im.buf[y*im.stride + 4*x + 1] = g;
+                    im.buf[y*im.stride + 4*x + 2] = b;
+                    im.buf[y*im.stride + 4*x + 3] = 0xff;
+                }
+            }
+
+            break;
+        }
+    }
+
+    pnm_destroy(pnmp);
+    return imp;
+}
+
+int image_u8x4_write_pnm(const image_u8x4_t *imp, const char *path)
+{
+    // copy struct by value to ensure common subexpression elimination occurs
+    const image_u8x4_t im = *imp;
+
+    FILE *f = fopen(path, "wb");
+    int res = 0;
+
+    if (f == NULL) {
+        res = -1;
+        goto finish;
+    }
+
+    // Only outputs to RGB
+    fprintf(f, "P6\n%d %d\n255\n", im.width, im.height);
+
+    for (int y = im.height-1; y >= 0; y--) {
+        for (int x = 0; x < im.width; x++) {
+
+            uint8_t r = im.buf[y*im.stride + 4*x + 0];
+            uint8_t g = im.buf[y*im.stride + 4*x + 1];
+            uint8_t b = im.buf[y*im.stride + 4*x + 2];
+
+            fwrite(&r, 1, 1, f);
+            fwrite(&g, 1, 1, f);
+            fwrite(&b, 1, 1, f);
+        }
+    }
+
+  finish:
+    if (f != NULL)
+        fclose(f);
+
+    return res;
+}
+
+void image_u8x4_write_pam(const image_u8x4_t *im, const char *path)
+{
+    FILE *f = fopen(path, "w");
+    fprintf(f, "P7\n");
+    fprintf(f, "WIDTH %d\n", im->width);
+    fprintf(f, "HEIGHT %d\n", im->height);
+    fprintf(f, "DEPTH 4\n");
+    fprintf(f, "MAXVAL 255\n");
+    fprintf(f, "TUPLTYPE RGB_ALPHA\n");
+    fprintf(f, "ENDHDR\n");
+
+    for (int y = 0; y < im->height; y++)
+        fwrite(&im->buf[y*im->stride], 1, 4*im->width, f);
+
+    fclose(f);
+
+}