diff --git a/lib/test_common.c b/lib/test_common.c
new file mode 100644
index 0000000..c19e34f
--- /dev/null
+++ b/lib/test_common.c
@@ -0,0 +1,190 @@
+#define STB_IMAGE_IMPLEMENTATION
+#define STB_IMAGE_WRITE_IMPLEMENTATION
+#include "test_common.h"
+#include "stb_image.h"
+#include "stb_image_write.h"
+#include <math.h>
+#include <sys/time.h>
+
+uint8_t *load_image(const char *path, int *width, int *height, int *channels) {
+    return stbi_load(path, width, height, channels, 4);
+}
+
+int save_image(const char *path, uint8_t *data, int width, int height, int channels) {
+    return stbi_write_png(path, width, height, channels, data, width * channels);
+}
+
+uint8_t *downsample_image(uint8_t *src, int sw, int sh, int sc, int *dw, int *dh, float scale) {
+    if (!src || sw <= 0 || sh <= 0 || sc <= 0 || scale <= 0) {
+        if (dw) *dw = 0;
+        if (dh) *dh = 0;
+        return NULL;
+    }
+
+    int tw = (int)(sw * scale);
+    int th = (int)(sh * scale);
+
+    if (tw < 1) tw = 1;
+    if (th < 1) th = 1;
+
+    uint8_t *dst = malloc(tw * th * sc);
+    if (!dst) return NULL;
+
+    float inv_scale = 1.0f / scale;
+    for (int y = 0; y < th; y++) {
+        for (int x = 0; x < tw; x++) {
+            float sx = (x + 0.5f) * inv_scale;
+            float sy = (y + 0.5f) * inv_scale;
+
+            int ix = (int)sx;
+            int iy = (int)sy;
+
+            if (sw > 1) {
+                ix = (ix < sw - 2) ? ix : sw - 2;
+            } else {
+                ix = 0;
+            }
+            if (sh > 1) {
+                iy = (iy < sh - 2) ? iy : sh - 2;
+            } else {
+                iy = 0;
+            }
+
+            if (ix < 0) ix = 0;
+            if (iy < 0) iy = 0;
+
+            float fx = sx - ix;
+            float fy = sy - iy;
+
+            if (sw == 1) fx = 0.0f;
+            if (sh == 1) fy = 0.0f;
+
+            for (int c = 0; c < sc; c++) {
+                uint8_t p00 = src[(iy * sw + ix) * sc + c];
+                uint8_t p01 = (sw > 1) ? src[(iy * sw + ix + 1) * sc + c] : p00;
+                uint8_t p10 = (sh > 1) ? src[((iy + 1) * sw + ix) * sc + c] : p00;
+                uint8_t p11 = (sw > 1 && sh > 1) ? src[((iy + 1) * sw + ix + 1) * sc + c] : p00;
+
+                float interp = p00 * (1 - fx) * (1 - fy) +
+                              p01 * fx * (1 - fy) +
+                              p10 * (1 - fx) * fy +
+                              p11 * fx * fy;
+
+                dst[(y * tw + x) * sc + c] = (uint8_t)(interp + 0.5f);
+            }
+        }
+    }
+
+    *dw = tw;
+    *dh = th;
+    return dst;
+}
+
+double get_time_ms(void) {
+    struct timeval tv;
+    gettimeofday(&tv, NULL);
+    return tv.tv_sec * 1000.0 + tv.tv_usec / 1000.0;
+}
+
+double run_benchmark(double (*fn)(void), int iterations) {
+    double warmup = fn();
+    (void)warmup;
+
+    double total = 0.0;
+    for (int i = 0; i < iterations; i++) {
+        total += fn();
+    }
+    return total / iterations;
+}
+
+int compare_images(uint8_t *a, uint8_t *b, int w, int h, int ch, float threshold) {
+    int max_diff = 0;
+    for (int i = 0; i < w * h * ch; i++) {
+        int diff = abs((int)a[i] - (int)b[i]);
+        if (diff > max_diff) max_diff = diff;
+        if (diff > (int)(threshold * 255.0f)) {
+            return 0;
+        }
+    }
+    return 1;
+}
+
+float compute_psnr(uint8_t *a, uint8_t *b, int w, int h, int ch) {
+    double mse = 0.0;
+    int total = w * h * ch;
+
+    for (int i = 0; i < total; i++) {
+        double diff = (double)a[i] - (double)b[i];
+        mse += diff * diff;
+    }
+
+    mse /= total;
+
+    if (mse < 1e-10) return 99.99f;
+
+    return (float)(10.0 * log10(255.0 * 255.0 / mse));
+}
+
+uint8_t *create_gradient_image(int w, int h) {
+    uint8_t *img = malloc(w * h * 4);
+    if (!img) return NULL;
+
+    for (int y = 0; y < h; y++) {
+        for (int x = 0; x < w; x++) {
+            int idx = (y * w + x) * 4;
+            img[idx + 0] = (uint8_t)((float)x / w * 255);
+            img[idx + 1] = (uint8_t)((float)y / h * 255);
+            img[idx + 2] = 128;
+            img[idx + 3] = 255;
+        }
+    }
+    return img;
+}
+
+uint8_t *create_noise_image(int w, int h, unsigned int seed) {
+    uint8_t *img = malloc(w * h * 4);
+    if (!img) return NULL;
+
+    srand(seed);
+    for (int i = 0; i < w * h * 4; i++) {
+        img[i] = (uint8_t)(rand() % 256);
+    }
+    return img;
+}
+
+uint8_t *create_uniform_image(int w, int h, uint8_t r, uint8_t g, uint8_t b) {
+    uint8_t *img = malloc(w * h * 4);
+    if (!img) return NULL;
+
+    for (int i = 0; i < w * h; i++) {
+        img[i * 4 + 0] = r;
+        img[i * 4 + 1] = g;
+        img[i * 4 + 2] = b;
+        img[i * 4 + 3] = 255;
+    }
+    return img;
+}
+
+uint8_t *create_checkerboard(int w, int h, int check_size) {
+    uint8_t *img = malloc(w * h * 4);
+    if (!img) return NULL;
+
+    for (int y = 0; y < h; y++) {
+        for (int x = 0; x < w; x++) {
+            int idx = (y * w + x) * 4;
+            int cx = x / check_size;
+            int cy = y / check_size;
+            if ((cx + cy) % 2 == 0) {
+                img[idx + 0] = 255;
+                img[idx + 1] = 255;
+                img[idx + 2] = 255;
+            } else {
+                img[idx + 0] = 0;
+                img[idx + 1] = 0;
+                img[idx + 2] = 0;
+            }
+            img[idx + 3] = 255;
+        }
+    }
+    return img;
+}