diff --git a/Makefile b/Makefile
index 6097a01..514efd1 100644
--- a/Makefile
+++ b/Makefile
@@ -29,7 +29,7 @@ else
 IMAGE_EXT := ppm
 endif
 
-COMMON_SOURCES := $(filter-out src/main.c src/spacetime_minkowski.c src/spacetime_schwarzschild.c,$(wildcard src/*.c))
+COMMON_SOURCES := $(filter-out src/main.c src/dummy_psf.c src/spacetime_minkowski.c src/spacetime_schwarzschild.c,$(wildcard src/*.c))
 PROVIDER_SOURCE := src/spacetime_$(SPACETIME).c
 BUILD_DIR := build/$(BUILD_TYPE)
 TARGET_BASENAME := $(SPACETIME)_sky
@@ -56,8 +56,11 @@ RENDER_LINKER := $(CC)
 else ifeq ($(PSF_BACKEND),hip)
 RENDER_LINKER := $(HIPCC)
 BUILD_CPPFLAGS += -DPSF_BACKEND_HIP
+else ifeq ($(PSF_BACKEND),dummy)
+RENDER_LINKER := $(CC)
+BUILD_CPPFLAGS += -DPSF_BACKEND_DUMMY
 else
-$(error Unknown PSF_BACKEND '$(PSF_BACKEND)'; choose cpu or hip)
+$(error Unknown PSF_BACKEND '$(PSF_BACKEND)'; choose cpu, hip, or dummy)
 endif
 
 ifeq ($(SPACETIME),minkowski)
@@ -80,10 +83,15 @@ endif
 
 ifeq ($(PSF_BACKEND),hip)
 TARGET := $(BUILD_DIR)/$(TARGET_BASENAME)_hip
+else ifeq ($(PSF_BACKEND),dummy)
+TARGET := $(BUILD_DIR)/$(TARGET_BASENAME)_dummy
 else
 TARGET := $(BUILD_DIR)/$(TARGET_BASENAME)
 endif
 RENDER_SOURCES := $(COMMON_SOURCES) $(PROVIDER_SOURCE) src/main.c
+ifeq ($(PSF_BACKEND),dummy)
+RENDER_SOURCES += src/dummy_psf.c
+endif
 RENDER_OBJECTS := $(patsubst %.c,$(OBJECT_DIR)/$(HDR_BUILD_TAG)/%.o,$(RENDER_SOURCES))
 ifeq ($(PSF_BACKEND),hip)
 HIP_PSF_OBJECT := $(OBJECT_DIR)/$(HDR_BUILD_TAG)/src/hip_psf.o
diff --git a/benchmarks/dummy_psf_chunks_2026-09-11/.gitignore b/benchmarks/dummy_psf_chunks_2026-09-11/.gitignore
new file mode 100644
index 0000000..c18dd8d
--- /dev/null
+++ b/benchmarks/dummy_psf_chunks_2026-09-11/.gitignore
@@ -0,0 +1 @@
+__pycache__/
diff --git a/benchmarks/dummy_psf_chunks_2026-09-11/run.py b/benchmarks/dummy_psf_chunks_2026-09-11/run.py
new file mode 100644
index 0000000..f9a5e82
--- /dev/null
+++ b/benchmarks/dummy_psf_chunks_2026-09-11/run.py
@@ -0,0 +1,99 @@
+#!/usr/bin/env python3
+"""Run the fixed full-catalog dummy diagnostic once without touching images."""
+
+import fcntl
+import hashlib
+import os
+from pathlib import Path
+import resource
+import shlex
+import signal
+import subprocess
+import time
+
+ROOT = Path(__file__).resolve().parents[2]
+LOG = Path(__file__).with_name("full_catalog.log")
+BINARY = ROOT / "build/Release/schwarzschild_sky_dummy"
+LENS = ROOT / "output/lens/schwarzschild_galactic_center_R100_45deg_16_4_4k_.grlens"
+PNG = ROOT / "output/imgs/2mass_galactic_center_schwarzschild_R100_4k_1e13_beta4.5_16_4-full-gpu.png"
+FITS = ROOT / "output/imgs/2mass_galactic_center_schwarzschild_R100_4k_1e13_beta4.5_16_4-full-gpu_HDR.fits"
+
+
+def digest(path):
+    return hashlib.sha256(path.read_bytes()).hexdigest()
+
+
+def main():
+    if LOG.exists():
+        raise RuntimeError(f"refusing to overwrite {LOG}")
+    for path in (BINARY, LENS, PNG, FITS):
+        if not path.is_file():
+            raise RuntimeError(f"required file is missing: {path}")
+    protected_before = {
+        path: (digest(path), path.stat().st_size, path.stat().st_mtime_ns)
+        for path in (PNG, FITS)
+    }
+    command = [
+        str(BINARY), "--verbose",
+        "--psf-relative-tail", "1e-8", "--psf-min-y", "0",
+        "--max-cache-psf-flux", "1e8",
+        "--all-sky-catalog", "assets/2mass/processed/all_sky",
+        "--exposure", "1e13", "--psf-fwhm-pixels", "2.7",
+        "--psf-moffat-beta", "4.5", "--catalog-load-workers", "4",
+        "--hdr-output", "--lens-map-input",
+        "output/lens/schwarzschild_galactic_center_R100_45deg_16_4_4k_.grlens",
+        "--output",
+        "output/imgs/2mass_galactic_center_schwarzschild_R100_4k_1e13_beta4.5_16_4-full-gpu.png",
+    ]
+    guard = open("/tmp/gr_dummy_psf_chunks.lock", "w")
+    fcntl.flock(guard, fcntl.LOCK_EX | fcntl.LOCK_NB)
+    env = dict(os.environ, OMP_NUM_THREADS="16", OMP_DYNAMIC="FALSE")
+    with LOG.open("x") as out:
+        out.write("COMMAND OMP_NUM_THREADS=16 OMP_DYNAMIC=FALSE " +
+                  shlex.join(command) + "\n")
+        out.write("GIT " + subprocess.check_output(
+            ["git", "rev-parse", "HEAD"], cwd=ROOT, text=True))
+        out.write("BINARY_SHA256 " + digest(BINARY) + "\n")
+        out.write("LENS_SHA256 " + digest(LENS) + "\n")
+        for path, state in protected_before.items():
+            out.write(
+                f"PROTECTED_BEFORE {path.relative_to(ROOT)} sha256={state[0]} "
+                f"size={state[1]} mtime_ns={state[2]}\n")
+        out.flush()
+        start = time.monotonic()
+        usage_start = resource.getrusage(resource.RUSAGE_CHILDREN)
+        process = subprocess.Popen(command, cwd=ROOT, env=env, stdout=out,
+                                   stderr=subprocess.STDOUT,
+                                   start_new_session=True)
+        try:
+            returncode = process.wait(timeout=600)
+        except subprocess.TimeoutExpired:
+            os.killpg(process.pid, signal.SIGKILL)
+            process.wait()
+            out.write("TIMEOUT killed and reaped process group\n")
+            raise
+        out.write(
+            f"PROCESS_WALL {time.monotonic() - start:.9f} EXIT {returncode}\n")
+        usage_end = resource.getrusage(resource.RUSAGE_CHILDREN)
+        out.write(
+            f"PROCESS_USER {usage_end.ru_utime - usage_start.ru_utime:.9f} "
+            f"PROCESS_SYSTEM {usage_end.ru_stime - usage_start.ru_stime:.9f} "
+            f"MAX_RSS_KIB {usage_end.ru_maxrss}\n")
+    protected_after = {
+        path: (digest(path), path.stat().st_size, path.stat().st_mtime_ns)
+        for path in (PNG, FITS)
+    }
+    if protected_after != protected_before:
+        raise RuntimeError("a protected render output changed")
+    with LOG.open("a") as out:
+        for path, state in protected_after.items():
+            out.write(
+                f"PROTECTED_AFTER {path.relative_to(ROOT)} sha256={state[0]} "
+                f"size={state[1]} mtime_ns={state[2]} unchanged=yes\n")
+    if returncode:
+        raise RuntimeError(f"dummy diagnostic exited {returncode}")
+    print(LOG)
+
+
+if __name__ == "__main__":
+    main()
diff --git a/build.md b/build.md
index dfbac17..dc55da9 100644
--- a/build.md
+++ b/build.md
@@ -104,6 +104,29 @@ times must not be added to GPU timings or interpreted as process CPU time.
 The two upload slots bound staging memory and allow CPU production ahead of GPU
 completion; copies and kernels still execute in order on one stream.
 
+### Diagnostic dummy PSF backend
+
+To inspect production chunk geometry without starting HIP or allocating an HDR
+framebuffer, build the diagnostic-only dummy backend:
+
+```sh
+make -j1 PSF_BACKEND=dummy SPACETIME=schwarzschild ENABLE_HDR=1 backend
+OMP_NUM_THREADS=16 OMP_DYNAMIC=FALSE \
+  ./build/Release/schwarzschild_sky_dummy --lens-map-input MAP.grlens \
+  --all-sky-catalog CATALOG_DIR --output PROTECTED_OR_UNUSED.png [normal PSF options]
+```
+
+The dummy executable requires an imported lens map and the PSF cache; it rejects
+`--psf-direct`. It runs the real OpenMP triangle scheduling, catalog query,
+inverse mapping, redshift/color/flux preparation, and cache/direct/min-Y
+classification, but records chunk statistics instead of accumulating pixels.
+`--output` and `--hdr-output` are accepted only for command parity: neither PNG
+nor FITS is created or modified. Reports separate full 16,384-event chunks from
+the final partial chunk of each worker and include event-producing triangle
+counts, occupied 32-pixel center tiles, bounding-box diagonals, and successive
+triangle-centroid jumps. This is a scheduling diagnostic, not a rendering or
+backend-performance benchmark.
+
 With both Minkowski binaries built using `ENABLE_HDR=1`,
 `python3 tests/test_hip_renderer.py build/Release/minkowski_sky build/Release/minkowski_sky_hip`
 runs small CPU/HIP fallback and min-Y comparisons sequentially. Each renderer
diff --git a/src/dummy_psf.c b/src/dummy_psf.c
new file mode 100644
index 0000000..25e58d5
--- /dev/null
+++ b/src/dummy_psf.c
@@ -0,0 +1,309 @@
+#include "dummy_psf.h"
+
+#include <math.h>
+#include <omp.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+enum { DUMMY_SELECTOR_TILE = 32 };
+
+typedef struct {
+  size_t worker, events, triangles, occupied_tiles;
+  double event_bbox_diagonal, triangle_bbox_diagonal;
+  double maximum_triangle_jump;
+  int adaptive_tile16;
+} DummyChunkSample;
+
+struct DummyPsfSink {
+  DummyChunkSample *samples;
+  size_t count, capacity, event_capacity;
+  size_t total_events;
+  int width, height, tiles_x, tiles_y;
+  int failed;
+  omp_lock_t lock;
+};
+
+struct DummyPsfChunk {
+  DummyPsfSink *sink;
+  uint32_t *tile_generation;
+  uint32_t generation;
+  size_t worker, events, triangles, occupied_tiles;
+  size_t last_triangle;
+  int have_event, have_triangle;
+  double event_min_x, event_max_x, event_min_y, event_max_y;
+  double triangle_min_x, triangle_max_x, triangle_min_y, triangle_max_y;
+  double last_triangle_x, last_triangle_y, maximum_triangle_jump;
+};
+
+static int append_sample(DummyPsfSink *sink, DummyChunkSample sample) {
+  int result = 0;
+  omp_set_lock(&sink->lock);
+  if (sink->failed) {
+    result = -1;
+  } else if (sink->count == sink->capacity) {
+    const size_t capacity = sink->capacity ? 2 * sink->capacity : 1024;
+    DummyChunkSample *samples =
+        capacity < sink->capacity || capacity > SIZE_MAX / sizeof *samples
+                                    ? NULL
+                                    : realloc(sink->samples,
+                                              capacity * sizeof *samples);
+    if (samples == NULL) {
+      sink->failed = 1;
+      result = -1;
+    } else {
+      sink->samples = samples;
+      sink->capacity = capacity;
+    }
+  }
+  if (!result) {
+    sink->samples[sink->count++] = sample;
+    sink->total_events += sample.events;
+  }
+  omp_unset_lock(&sink->lock);
+  return result;
+}
+
+int dummy_psf_sink_create(DummyPsfSink **out, int width, int height,
+                          size_t event_capacity) {
+  if (out == NULL || width <= 0 || height <= 0 || event_capacity == 0)
+    return -1;
+  DummyPsfSink *sink = calloc(1, sizeof *sink);
+  if (sink == NULL)
+    return -1;
+  sink->width = width;
+  sink->height = height;
+  sink->tiles_x = (width + DUMMY_SELECTOR_TILE - 1) / DUMMY_SELECTOR_TILE;
+  sink->tiles_y = (height + DUMMY_SELECTOR_TILE - 1) / DUMMY_SELECTOR_TILE;
+  sink->event_capacity = event_capacity;
+  omp_init_lock(&sink->lock);
+  *out = sink;
+  return 0;
+}
+
+int dummy_psf_chunk_create(DummyPsfChunk **out, DummyPsfSink *sink,
+                           size_t worker_id) {
+  if (out == NULL || sink == NULL)
+    return -1;
+  DummyPsfChunk *chunk = calloc(1, sizeof *chunk);
+  if (chunk == NULL)
+    return -1;
+  const size_t tile_count = (size_t)sink->tiles_x * sink->tiles_y;
+  chunk->tile_generation = calloc(tile_count, sizeof *chunk->tile_generation);
+  if (chunk->tile_generation == NULL) {
+    free(chunk);
+    return -1;
+  }
+  chunk->sink = sink;
+  chunk->worker = worker_id;
+  chunk->generation = 1;
+  *out = chunk;
+  return 0;
+}
+
+static void reset_chunk(DummyPsfChunk *chunk) {
+  chunk->events = 0;
+  chunk->triangles = 0;
+  chunk->occupied_tiles = 0;
+  chunk->have_event = 0;
+  chunk->have_triangle = 0;
+  chunk->maximum_triangle_jump = 0.0;
+  if (++chunk->generation == 0) {
+    const size_t count = (size_t)chunk->sink->tiles_x * chunk->sink->tiles_y;
+    memset(chunk->tile_generation, 0, count * sizeof *chunk->tile_generation);
+    chunk->generation = 1;
+  }
+}
+
+int dummy_psf_chunk_flush(DummyPsfChunk *chunk) {
+  if (chunk == NULL)
+    return -1;
+  if (chunk->events == 0)
+    return 0;
+  const double event_diagonal =
+      hypot(chunk->event_max_x - chunk->event_min_x,
+            chunk->event_max_y - chunk->event_min_y);
+  const double triangle_diagonal =
+      hypot(chunk->triangle_max_x - chunk->triangle_min_x,
+            chunk->triangle_max_y - chunk->triangle_min_y);
+  const DummyChunkSample sample = {
+      .worker = chunk->worker,
+      .events = chunk->events,
+      .triangles = chunk->triangles,
+      .occupied_tiles = chunk->occupied_tiles,
+      .event_bbox_diagonal = event_diagonal,
+      .triangle_bbox_diagonal = triangle_diagonal,
+      .maximum_triangle_jump = chunk->maximum_triangle_jump,
+      .adaptive_tile16 = chunk->events >= 8192 && chunk->occupied_tiles != 0 &&
+                         chunk->events / chunk->occupied_tiles >= 32};
+  const int result = append_sample(chunk->sink, sample);
+  reset_chunk(chunk);
+  return result;
+}
+
+int dummy_psf_chunk_emit(DummyPsfChunk *chunk, const PsfCachedEvent *event,
+                         size_t triangle, double triangle_center_x,
+                         double triangle_center_y) {
+  if (chunk == NULL || event == NULL)
+    return -1;
+  if (chunk->events == chunk->sink->event_capacity &&
+      dummy_psf_chunk_flush(chunk))
+    return -1;
+
+  if (!chunk->have_event) {
+    chunk->event_min_x = chunk->event_max_x = event->x;
+    chunk->event_min_y = chunk->event_max_y = event->y;
+    chunk->have_event = 1;
+  } else {
+    chunk->event_min_x = fmin(chunk->event_min_x, event->x);
+    chunk->event_max_x = fmax(chunk->event_max_x, event->x);
+    chunk->event_min_y = fmin(chunk->event_min_y, event->y);
+    chunk->event_max_y = fmax(chunk->event_max_y, event->y);
+  }
+
+  const int pixel_x = (int)floor(event->x);
+  const int pixel_y = (int)floor(event->y);
+  if (pixel_x >= 0 && pixel_x < chunk->sink->width && pixel_y >= 0 &&
+      pixel_y < chunk->sink->height) {
+    const size_t tile = (size_t)(pixel_y / DUMMY_SELECTOR_TILE) *
+                            chunk->sink->tiles_x +
+                        pixel_x / DUMMY_SELECTOR_TILE;
+    if (chunk->tile_generation[tile] != chunk->generation) {
+      chunk->tile_generation[tile] = chunk->generation;
+      ++chunk->occupied_tiles;
+    }
+  }
+
+  if (!chunk->have_triangle || triangle != chunk->last_triangle) {
+    if (!chunk->have_triangle) {
+      chunk->triangle_min_x = chunk->triangle_max_x = triangle_center_x;
+      chunk->triangle_min_y = chunk->triangle_max_y = triangle_center_y;
+      chunk->have_triangle = 1;
+    } else {
+      chunk->triangle_min_x = fmin(chunk->triangle_min_x, triangle_center_x);
+      chunk->triangle_max_x = fmax(chunk->triangle_max_x, triangle_center_x);
+      chunk->triangle_min_y = fmin(chunk->triangle_min_y, triangle_center_y);
+      chunk->triangle_max_y = fmax(chunk->triangle_max_y, triangle_center_y);
+      chunk->maximum_triangle_jump =
+          fmax(chunk->maximum_triangle_jump,
+               hypot(triangle_center_x - chunk->last_triangle_x,
+                     triangle_center_y - chunk->last_triangle_y));
+    }
+    chunk->last_triangle = triangle;
+    chunk->last_triangle_x = triangle_center_x;
+    chunk->last_triangle_y = triangle_center_y;
+    ++chunk->triangles;
+  }
+  ++chunk->events;
+  return 0;
+}
+
+void dummy_psf_chunk_destroy(DummyPsfChunk *chunk) {
+  if (chunk == NULL)
+    return;
+  (void)dummy_psf_chunk_flush(chunk);
+  free(chunk->tile_generation);
+  free(chunk);
+}
+
+static int compare_double(const void *left, const void *right) {
+  const double a = *(const double *)left;
+  const double b = *(const double *)right;
+  return (a > b) - (a < b);
+}
+
+static double percentile(const double *values, size_t count, double fraction) {
+  if (count == 0)
+    return 0.0;
+  const double position = fraction * (count - 1);
+  const size_t low = (size_t)floor(position);
+  const size_t high = low + 1 < count ? low + 1 : low;
+  return values[low] + (values[high] - values[low]) * (position - low);
+}
+
+static void report_group(const DummyPsfSink *sink, int full_only,
+                         const char *label) {
+  size_t count = 0, adaptive = 0;
+  for (size_t i = 0; i < sink->count; ++i)
+    if (!full_only || sink->samples[i].events == sink->event_capacity)
+      ++count;
+  if (count == 0) {
+    fprintf(stderr, "Dummy PSF %s chunks: none\n", label);
+    return;
+  }
+  double *events = count > SIZE_MAX / (6 * sizeof *events)
+                       ? NULL
+                       : malloc(6 * count * sizeof *events);
+  if (events == NULL) {
+    fputs("Dummy PSF report allocation failed\n", stderr);
+    return;
+  }
+  double *triangles = events + count;
+  double *tiles = triangles + count;
+  double *event_distance = tiles + count;
+  double *triangle_distance = event_distance + count;
+  double *maximum_jump = triangle_distance + count;
+  size_t next = 0;
+  for (size_t i = 0; i < sink->count; ++i) {
+    const DummyChunkSample *sample = &sink->samples[i];
+    if (full_only && sample->events != sink->event_capacity)
+      continue;
+    events[next] = sample->events;
+    triangles[next] = sample->triangles;
+    tiles[next] = sample->occupied_tiles;
+    event_distance[next] = sample->event_bbox_diagonal;
+    triangle_distance[next] = sample->triangle_bbox_diagonal;
+    maximum_jump[next] = sample->maximum_triangle_jump;
+    adaptive += sample->adaptive_tile16;
+    ++next;
+  }
+  double *series[] = {events, triangles, tiles, event_distance,
+                      triangle_distance, maximum_jump};
+  const char *names[] = {"events", "distinct_triangles", "occupied_32px_tiles",
+                         "event_bbox_diagonal_px",
+                         "triangle_centroid_bbox_diagonal_px",
+                         "maximum_successive_triangle_jump_px"};
+  for (size_t field = 0; field < 6; ++field) {
+    qsort(series[field], count, sizeof **series, compare_double);
+    fprintf(stderr,
+            "Dummy PSF %s %s: min=%.3f p10=%.3f p25=%.3f p50=%.3f "
+            "p75=%.3f p90=%.3f p99=%.3f max=%.3f\n",
+            label, names[field], series[field][0],
+            percentile(series[field], count, 0.10),
+            percentile(series[field], count, 0.25),
+            percentile(series[field], count, 0.50),
+            percentile(series[field], count, 0.75),
+            percentile(series[field], count, 0.90),
+            percentile(series[field], count, 0.99), series[field][count - 1]);
+  }
+  fprintf(stderr,
+          "Dummy PSF %s adaptive criterion: %zu/%zu chunks tile16-eligible "
+          "(events>=8192 and events/occupied_32px_tiles>=32)\n",
+          label, adaptive, count);
+  free(events);
+}
+
+void dummy_psf_sink_report(const DummyPsfSink *sink) {
+  if (sink == NULL)
+    return;
+  size_t full = 0;
+  for (size_t i = 0; i < sink->count; ++i)
+    full += sink->samples[i].events == sink->event_capacity;
+  fprintf(stderr,
+          "Dummy PSF diagnostic only: no HDR or image was accumulated/written.\n"
+          "Dummy PSF chunks: total=%zu full=%zu partial=%zu events=%zu "
+          "capacity=%zu selector_tile=%dpx\n",
+          sink->count, full, sink->count - full, sink->total_events,
+          sink->event_capacity, DUMMY_SELECTOR_TILE);
+  report_group(sink, 0, "all");
+  report_group(sink, 1, "full");
+}
+
+void dummy_psf_sink_destroy(DummyPsfSink *sink) {
+  if (sink == NULL)
+    return;
+  omp_destroy_lock(&sink->lock);
+  free(sink->samples);
+  free(sink);
+}
diff --git a/src/dummy_psf.h b/src/dummy_psf.h
new file mode 100644
index 0000000..8c16729
--- /dev/null
+++ b/src/dummy_psf.h
@@ -0,0 +1,25 @@
+#ifndef DUMMY_PSF_H
+#define DUMMY_PSF_H
+
+#include "optics.h"
+
+#include <stddef.h>
+
+typedef struct DummyPsfSink DummyPsfSink;
+typedef struct DummyPsfChunk DummyPsfChunk;
+
+/* Diagnostic-only consumer for the production PSF event stream. It preserves
+ * per-worker chunk boundaries but never accumulates or writes an HDR image. */
+int dummy_psf_sink_create(DummyPsfSink **out, int width, int height,
+                          size_t event_capacity);
+int dummy_psf_chunk_create(DummyPsfChunk **out, DummyPsfSink *sink,
+                           size_t worker_id);
+int dummy_psf_chunk_emit(DummyPsfChunk *chunk, const PsfCachedEvent *event,
+                         size_t triangle, double triangle_center_x,
+                         double triangle_center_y);
+int dummy_psf_chunk_flush(DummyPsfChunk *chunk);
+void dummy_psf_chunk_destroy(DummyPsfChunk *chunk);
+void dummy_psf_sink_report(const DummyPsfSink *sink);
+void dummy_psf_sink_destroy(DummyPsfSink *sink);
+
+#endif
diff --git a/src/frame.c b/src/frame.c
index 38d1857..9f33894 100644
--- a/src/frame.c
+++ b/src/frame.c
@@ -3,6 +3,9 @@
 #ifdef PSF_BACKEND_HIP
 #include "hip_psf.h"
 #endif
+#ifdef PSF_BACKEND_DUMMY
+#include "dummy_psf.h"
+#endif
 
 #include "optics.h"
 
@@ -138,6 +141,11 @@ typedef struct {
   double submit_seconds;
   char hip_message[256];
   HipPsfTiming hip_timing;
+#endif
+#ifdef PSF_BACKEND_DUMMY
+  DummyPsfSink *dummy;
+  DummyPsfChunk *dummy_chunk;
+  int borrowed_dummy;
 #endif
   int failed;
 } PsfEventSink;
@@ -155,6 +163,16 @@ static int psf_event_sink_init(PsfEventSink *sink, double *hdr, int width,
   *sink = (PsfEventSink){.hdr = hdr, .width = width, .height = height,
                          .cache = cache};
   if (cache != NULL) {
+#ifdef PSF_BACKEND_DUMMY
+    if (dummy_psf_sink_create(&sink->dummy, width, height,
+                              PSF_EVENT_SINK_CAPACITY)) {
+      fputs("Dummy PSF backend initialization failed\n", stderr);
+      dummy_psf_sink_destroy(sink->dummy);
+      sink->dummy = NULL;
+      sink->failed = 1;
+      return -1;
+    }
+#else
     sink->events = malloc(PSF_EVENT_SINK_CAPACITY * sizeof *sink->events);
     if (sink->events == NULL) {
 #ifdef PSF_BACKEND_HIP
@@ -174,6 +192,7 @@ static int psf_event_sink_init(PsfEventSink *sink, double *hdr, int width,
       sink->events = NULL;
       return -1;
     }
+#endif
 #endif
   }
   return 0;
@@ -182,6 +201,10 @@ static int psf_event_sink_init(PsfEventSink *sink, double *hdr, int width,
 static int psf_event_sink_flush_unlocked(PsfEventSink *sink) {
   if (sink->failed)
     return -1;
+#ifdef PSF_BACKEND_DUMMY
+  if (sink->dummy_chunk != NULL)
+    return dummy_psf_chunk_flush(sink->dummy_chunk);
+#endif
 #ifdef PSF_BACKEND_HIP
   if (sink->hip != NULL) {
     if (hip_psf_sink_submit(sink->hip, sink->events, sink->count,
@@ -233,6 +256,7 @@ static int psf_event_sink_finish_for_cpu(PsfEventSink *sink) {
   return 0;
 }
 
+#ifndef PSF_BACKEND_DUMMY
 static int psf_event_sink_resume_gpu(PsfEventSink *sink) {
 #ifdef PSF_BACKEND_HIP
   if (sink->hip != NULL && hip_psf_sink_load_hdr(sink->hip, sink->hdr,
@@ -246,8 +270,22 @@ static int psf_event_sink_resume_gpu(PsfEventSink *sink) {
 #endif
   return 0;
 }
+#endif
 
 static int psf_event_sink_destroy(PsfEventSink *sink) {
+#ifdef PSF_BACKEND_DUMMY
+  int dummy_result = sink->dummy_chunk != NULL
+                         ? dummy_psf_chunk_flush(sink->dummy_chunk)
+                         : 0;
+  dummy_psf_chunk_destroy(sink->dummy_chunk);
+  sink->dummy_chunk = NULL;
+  if (!sink->borrowed_dummy) {
+    dummy_psf_sink_report(sink->dummy);
+    dummy_psf_sink_destroy(sink->dummy);
+    sink->dummy = NULL;
+  }
+  return dummy_result;
+#endif
 #ifdef PSF_BACKEND_HIP
   if (sink->borrowed_hip) {
     const int result = psf_event_sink_flush(sink);
@@ -267,10 +305,22 @@ static int psf_event_sink_destroy(PsfEventSink *sink) {
   return result;
 }
 
-#if FRAME_PSF_EVENT_SINK || defined(PSF_BACKEND_HIP)
-static void psf_event_sink_emit(PsfEventSink *sink, const PsfCachedEvent *event) {
+#if FRAME_PSF_EVENT_SINK || defined(PSF_BACKEND_HIP) || defined(PSF_BACKEND_DUMMY)
+static void psf_event_sink_emit(PsfEventSink *sink, const PsfCachedEvent *event,
+                                size_t triangle, double triangle_center_x,
+                                double triangle_center_y) {
   if (sink->failed)
     return;
+#ifdef PSF_BACKEND_DUMMY
+  if (dummy_psf_chunk_emit(sink->dummy_chunk, event, triangle,
+                           triangle_center_x, triangle_center_y))
+    sink->failed = 1;
+  return;
+#else
+  (void)triangle;
+  (void)triangle_center_x;
+  (void)triangle_center_y;
+#endif
   if (sink->events == NULL) {
     splat_prepared_cached_event(sink->hdr, sink->width, sink->height, event, sink->cache);
     return;
@@ -1129,6 +1179,9 @@ static int splat_catalog_tile(const Star *stars, size_t count,
 #endif
     if (direct_fallback == 1) {
       /* Exclude every other submit and fallback until HDR is back on device. */
+#ifdef PSF_BACKEND_DUMMY
+      if (psf_event_sink_flush(context->event_sink)) return -1;
+#else
 #ifdef PSF_BACKEND_HIP
       const double submit_start = omp_get_wtime();
       if (context->event_sink->hip_lock)
@@ -1147,9 +1200,17 @@ static int splat_catalog_tile(const Star *stars, size_t count,
       context->event_sink->submit_seconds += omp_get_wtime() - submit_start;
 #endif
       if (failed) return -1;
+#endif
     } else if (direct_fallback != 3) {
-#if FRAME_PSF_EVENT_SINK || defined(PSF_BACKEND_HIP)
-      psf_event_sink_emit(context->event_sink, &event);
+#if FRAME_PSF_EVENT_SINK || defined(PSF_BACKEND_HIP) || defined(PSF_BACKEND_DUMMY)
+      const double triangle_center_x =
+          (context->vertex[0]->image_x + context->vertex[1]->image_x +
+           context->vertex[2]->image_x) / 3.0;
+      const double triangle_center_y =
+          (context->vertex[0]->image_y + context->vertex[1]->image_y +
+           context->vertex[2]->image_y) / 3.0;
+      psf_event_sink_emit(context->event_sink, &event, context->triangle_index,
+                          triangle_center_x, triangle_center_y);
 #else
       splat_prepared_cached_event(context->hdr, context->width, context->height,
                                   &event, context->psf_cache);
@@ -1319,6 +1380,83 @@ size_t frame_splat_catalog(const FrameLensMesh *mesh,
     progress->callback(progress->context, FRAME_SPLAT_PROGRESS_BEGIN, 0,
                        mesh->triangle_count);
 
+#ifdef PSF_BACKEND_DUMMY
+  PsfEventSink owner;
+  if (psf_event_sink_init(&owner, hdr, width, height, psf_cache)) return SIZE_MAX;
+  size_t dummy_images = 0, dummy_direct = 0, dummy_clipped = 0,
+         dummy_discarded = 0;
+  int dummy_failed = 0, dummy_workers = 0;
+  const double dummy_start = omp_get_wtime();
+#ifdef GR_DEBUG
+  double dummy_max_magnification = 0.0;
+  size_t dummy_clamped = 0;
+#pragma omp parallel reduction(+ : dummy_images, dummy_direct, dummy_clipped, dummy_discarded, dummy_clamped) reduction(max : dummy_failed, dummy_max_magnification)
+#else
+#pragma omp parallel reduction(+ : dummy_images, dummy_direct, dummy_clipped, dummy_discarded) reduction(max : dummy_failed)
+#endif
+  {
+#pragma omp single
+    dummy_workers = omp_get_num_threads();
+    const size_t worker = (size_t)omp_get_thread_num();
+    PsfEventSink local = {.hdr = hdr, .width = width, .height = height,
+        .cache = psf_cache, .dummy = owner.dummy, .borrowed_dummy = 1};
+    if (dummy_psf_chunk_create(&local.dummy_chunk, owner.dummy, worker)) {
+      fputs("Dummy PSF worker chunk initialization failed\n", stderr);
+      local.failed = 1;
+    }
+    size_t completed = 0, next_report = 8;
+    if (progress && progress->worker_callback)
+      progress->worker_callback(progress->context, worker,
+                                (size_t)dummy_workers, 0, 0);
+#pragma omp for schedule(dynamic, 1) nowait
+    for (size_t t = 0; t < mesh->triangle_count; ++t) {
+      if (local.failed) continue;
+      const CatalogSplatStats stats = splat_catalog_triangles(
+          mesh, catalog, hdr, width, height, exposure, psf, psf_cache,
+          max_magnification, max_cache_psf_flux, psf_relative_tail, psf_min_y,
+          t, t + 1, &local);
+      dummy_images += stats.images;
+      dummy_direct += stats.direct_fallbacks;
+      dummy_clipped += stats.cached_wing_clipped;
+      dummy_discarded += stats.discarded_below_min_y;
+      dummy_failed |= stats.failed;
+#ifdef GR_DEBUG
+      dummy_max_magnification = fmax(dummy_max_magnification,
+                                     stats.max_raw_magnification);
+      dummy_clamped += stats.magnification_clamped_triangles;
+#endif
+      ++completed;
+      if (progress && progress->worker_callback && completed == next_report) {
+        progress->worker_callback(progress->context, worker,
+                                  (size_t)dummy_workers, completed, 0);
+        if (next_report <= SIZE_MAX / 2) next_report *= 2;
+      }
+    }
+    if (psf_event_sink_destroy(&local)) dummy_failed = 1;
+    if (progress && progress->worker_callback)
+      progress->worker_callback(progress->context, worker,
+                                (size_t)dummy_workers, completed, 1);
+  }
+  if (psf_event_sink_destroy(&owner)) dummy_failed = 1;
+  fprintf(stderr,
+          "Dummy PSF producers: %d workers; classification/chunk wall %.3f s\n",
+          dummy_workers, omp_get_wtime() - dummy_start);
+  copy_psf_splat_stats(psf_stats, (CatalogSplatStats){
+      .images = dummy_images, .direct_fallbacks = dummy_direct,
+      .cached_wing_clipped = dummy_clipped,
+      .discarded_below_min_y = dummy_discarded,
+#ifdef GR_DEBUG
+      .max_raw_magnification = dummy_max_magnification,
+      .magnification_clamped_triangles = dummy_clamped,
+#endif
+  });
+  if (dummy_failed) return SIZE_MAX;
+  if (progress != NULL && progress->callback != NULL)
+    progress->callback(progress->context, FRAME_SPLAT_PROGRESS_END,
+                       mesh->triangle_count, mesh->triangle_count);
+  return dummy_images;
+#endif
+
 #ifdef PSF_BACKEND_HIP
   /* CPU workers own only bounded event chunks. A single device cache/HDR is
    * borrowed under a coarse submission lock, never duplicated per worker. */
diff --git a/src/main.c b/src/main.c
index ae8e5b6..87711db 100644
--- a/src/main.c
+++ b/src/main.c
@@ -445,8 +445,13 @@ static void report_splat_progress(void *context, FrameSplatProgressStage stage,
             progress->frame_id, total);
     break;
   case FRAME_SPLAT_PROGRESS_END:
+#ifdef PSF_BACKEND_DUMMY
+    fprintf(stderr, "Frame %zu: catalog classification finished in %.1f s; reporting chunk statistics...\n",
+            progress->frame_id, omp_get_wtime() - progress->splat_start);
+#else
     fprintf(stderr, "Frame %zu: catalog splatting finished in %.1f s; writing image...\n",
             progress->frame_id, omp_get_wtime() - progress->splat_start);
+#endif
     break;
   }
 }
@@ -922,7 +927,15 @@ static int render_lens_map(const Settings *s, StarCatalog *catalog) {
       }
       output_path = movie_path;
     }
+#ifdef PSF_BACKEND_DUMMY
+    (void)output_path;
+#endif
+#ifdef PSF_BACKEND_DUMMY
+    /* The dummy backend classifies real events but never touches pixels. */
+    double *hdr = calloc(1, sizeof *hdr);
+#else
     double *hdr = calloc((size_t)map.width * map.height * 3, sizeof *hdr);
+#endif
     if (hdr == NULL) { result = -1; break; }
     CatalogPrefetchStats prefetch = {0};
     PsfSplatStats psf_stats = {0};
@@ -945,7 +958,12 @@ static int render_lens_map(const Settings *s, StarCatalog *catalog) {
       break;
     }
     if (s->draw_mesh)
+#ifdef PSF_BACKEND_DUMMY
+      fputs("Dummy PSF backend ignores --draw-mesh.\n", stderr);
+#else
       frame_draw_mesh(&map.frames[i].mesh, hdr, map.width, map.height, 0.5, 0.5);
+#endif
+#ifndef PSF_BACKEND_DUMMY
 #ifdef ENABLE_HDR_OUTPUT
     if (s->write_hdr_output &&
         write_hdr_fits(s->hdr_output_path, hdr, map.width, map.height,
@@ -960,6 +978,13 @@ static int render_lens_map(const Settings *s, StarCatalog *catalog) {
             images, catalog->count, output_path, write_result == 0 ? "ok" : "write failed");
     psf_kernel_cache_report(&s->psf_cache, &psf_stats, stderr);
     if (write_result) { result = -1; break; }
+#else
+    free(hdr);
+    fprintf(stderr,
+            "Dummy PSF classified %zu images from %zu catalog stars; no HDR, PNG, or PPM was written.\n",
+            images, catalog->count);
+    psf_kernel_cache_report(&s->psf_cache, &psf_stats, stderr);
+#endif
   }
   lens_map_destroy(&map);
   return result;
@@ -1026,6 +1051,20 @@ int main(int argc, char **argv) {
     fputs("--lens-map-input and --lens-map-output are mutually exclusive.\n", stderr);
     return 2;
   }
+#ifdef PSF_BACKEND_DUMMY
+  if (settings.lens_map_input_path == NULL) {
+    fputs("The dummy PSF backend requires --lens-map-input and never traces or writes images.\n",
+          stderr);
+    return 2;
+  }
+  if (settings.psf_direct) {
+    fputs("The dummy PSF backend measures cache-event chunks and does not support --psf-direct.\n",
+          stderr);
+    return 2;
+  }
+  fputs("Dummy PSF backend: --output and --hdr-output are accepted for command parity but no image files will be written.\n",
+        stderr);
+#endif
 #ifdef ENABLE_HDR_OUTPUT
   if (settings.frames_dir != NULL && settings.write_hdr_output) {
     fputs("--hdr-output is available only for a single-frame render.\n", stderr);
@@ -1073,8 +1112,17 @@ int main(int argc, char **argv) {
     fprintf(stderr, "Created test catalog: %s\n", settings.catalog_path);
   }
   if (!settings.psf_direct && psf_kernel_cache_init(&settings.psf_cache, &settings.psf,
-                                                     settings.psf_relative_tail))
+                                                     settings.psf_relative_tail)) {
+#ifdef PSF_BACKEND_DUMMY
+    fputs("PSF cache construction failed; dummy chunk statistics are unavailable.\n",
+          stderr);
+    catalog_destroy(&catalog);
+    spacetime_destroy(&spacetime);
+    return 1;
+#else
     fputs("PSF cache construction failed; using direct evaluator.\n", stderr);
+#endif
+  }
   psf_kernel_cache_report_ready(&settings.psf_cache, stderr);
   if (settings.lens_map_input_path != NULL) {
     const int result = render_lens_map(&settings, &catalog);