diff --git a/changes/hdr-calibration.md b/changes/hdr-calibration.md
new file mode 100644
index 00000000..c733a31a
--- /dev/null
+++ b/changes/hdr-calibration.md
@@ -0,0 +1,16 @@
+bump: patch
+type: feat
+**HDR calibration, and two HDR fixes** — the HDR10 picture follows the player's display instead of one fixed curve.
+
+- **`r3d_hdr_calibrate(peak, paper, black)`** — nits as float bits: the brightest the display shows (100-10000),
+  where the picture's and the interface's white sit (80-1000, never above the peak) and how far the darkest shade is
+  lifted (0-5, fading out by paper white). The tonemap's and the overlay's HDR10 variants read them, and the display's
+  HDR metadata is sent again with the new peak. The defaults are the old constants: 1000, 200 and 0.
+- **`ov_hdr_nits(nits)` / `ov_hdr_paper()`** — what the overlay draws next is at that many nits on an HDR10 frame,
+  for a calibration screen's test patches; it closes the batch so far. No effect on an SDR frame.
+- **Fixed: a crash toggling HDR on the Vulkan renderer.** `gpu_caps_probe()` made and destroyed a second Vulkan
+  instance under NVIDIA Streamline's interposer; the next swapchain rebuild then called through a pointer that
+  instance had left behind, at address 0. With the Vulkan renderer running, the probe asks its instance instead.
+- **Fixed: yellow read as red in HDR.** The overlay drew sRGB values straight into the HDR10 swapchain (it now has an
+  HDR10 variant, chosen while `gpu_hdr_active()`), and the tonemap extended highlights per channel, which boosted a
+  bright yellow's red far more than its green; it now brightens the graded colour by one factor.
diff --git a/packages/ludic.render3d/gpu.ludic b/packages/ludic.render3d/gpu.ludic
index 0fc54f3f..9db0acc8 100644
--- a/packages/ludic.render3d/gpu.ludic
+++ b/packages/ludic.render3d/gpu.ludic
@@ -337,9 +337,18 @@ function gpu_caps_probe() -> void {
   Vk.zero(ici, VkInstanceCreateInfo_sizeof)
   Vk.put_i32(ici, VkInstanceCreateInfo_sType, VK_STRUCTURE_TYPE_INSTANCE_CREATE_INFO)
   Vk.put_ptr(ici, VkInstanceCreateInfo_pApplicationInfo, app)
-  let out = bytes(8)
-  if Vk.create_instance(ici, null, out) != VK_SUCCESS { return }
-  let inst = Vk.get_ptr(out, 0)
+  # With the Vulkan renderer running, ask its own instance: the renderer's loader is NVIDIA Streamline's
+  # interposer, and a second instance made and destroyed under it is what this avoids.
+  var inst: pointer = null
+  var own = false
+  if gpu_kind == GPU_VK and gvk_ready {
+    inst = gvk_inst
+  } else {
+    let out = bytes(8)
+    if Vk.create_instance(ici, null, out) != VK_SUCCESS { return }
+    inst = Vk.get_ptr(out, 0)
+    own = true
+  }
   Vk.put_i32(cnt, 0, 0)
   Vk.enumerate_physical_devices(inst, cnt, null)
   let nd = Vk.get_i32(cnt, 0)
@@ -385,7 +394,7 @@ function gpu_caps_probe() -> void {
     gpu_cap_mesh = gpu_ext_in(dexts, ne, VK_EXT_MESH_SHADER_EXTENSION_NAME)
     gpu_cap_reflex = gpu_ext_in(dexts, ne, VK_NV_LOW_LATENCY_2_EXTENSION_NAME)
   }
-  Vk.destroy_instance(inst, null)
+  if own { Vk.destroy_instance(inst, null) }
   print(`r3d: gpu caps: {gpu_cap_device} vulkan {gpu_cap_vulkan} floor {gpu_cap_floor} rt {gpu_cap_rt} mesh {gpu_cap_mesh} rtx {gpu_cap_rtx} reflex {gpu_cap_reflex} hdr {gpu_cap_hdr}`)
 }
 
diff --git a/packages/ludic.render3d/gpu_vk_draw.ludic b/packages/ludic.render3d/gpu_vk_draw.ludic
index fdbe74dc..1abe2cda 100644
--- a/packages/ludic.render3d/gpu_vk_draw.ludic
+++ b/packages/ludic.render3d/gpu_vk_draw.ludic
@@ -973,7 +973,28 @@ function r3d_hdr(on: bool) -> void {
 function gpu_hdr_active() -> bool { return gpu_kind == GPU_VK and gvk_hdr_on }
 function gvk_screen_fmt() -> int { if gvk_hdr_on { return GL_RGB10_A2 };  return GL_RGBA8 }
 
-# what the picture is: graded in BT.709 around D65, highlights to 1000 nits, a 200-nit average
+# The player's calibration of their display, in nits (float bits): the brightest it shows, where the
+# picture's and the interface's white sit, and how far the darkest shade is lifted. Displays differ by
+# an order of magnitude - a 400-nit monitor and a 2000-nit television - and one fixed curve either
+# clips the first's highlights flat or leaves the second dim.
+var r3d_hdr_peak: int = 0             # 0 until r3d_hdr_calibrate: 1000
+var r3d_hdr_paper: int = 0            # 200
+var r3d_hdr_black: int = 0            # 0
+function r3d_hdr_peak_nits() -> int { if r3d_hdr_peak == 0 { return fi(1000) };  return r3d_hdr_peak }
+function r3d_hdr_paper_nits() -> int { if r3d_hdr_paper == 0 { return fi(200) };  return r3d_hdr_paper }
+function r3d_hdr_black_nits() -> int { return r3d_hdr_black }
+function r3d_hdr_calibrate(peak: int, paper: int, black: int) -> void {
+  var pk = f_clamp(peak, fi(100), fi(10000))
+  let pp = f_clamp(paper, fi(80), fi(1000))
+  if f_ls(pk, pp) { pk = pp }
+  let bl = f_clamp(black, F_ZERO, fi(5))
+  if pk == r3d_hdr_peak and pp == r3d_hdr_paper and bl == r3d_hdr_black { return }
+  r3d_hdr_peak = pk;  r3d_hdr_paper = pp;  r3d_hdr_black = bl
+  # the display is told what the picture now reaches
+  if gvk_hdr_on and gvk_has_hdr_meta and gvk_swap != 0 { gvk_hdr_metadata() }
+}
+
+# what the picture is: graded in BT.709 around D65, highlights to the calibrated peak, paper white average
 function gvk_hdr_metadata() -> void {
   let md = bytes(VkHdrMetadataEXT_sizeof)
   Vk.zero(md, VkHdrMetadataEXT_sizeof)
@@ -982,10 +1003,10 @@ function gvk_hdr_metadata() -> void {
   Vk.put_i32(md, VkHdrMetadataEXT_displayPrimaryGreen + VkXYColorEXT_x, fl(0.30));  Vk.put_i32(md, VkHdrMetadataEXT_displayPrimaryGreen + VkXYColorEXT_y, fl(0.60))
   Vk.put_i32(md, VkHdrMetadataEXT_displayPrimaryBlue + VkXYColorEXT_x, fl(0.15));  Vk.put_i32(md, VkHdrMetadataEXT_displayPrimaryBlue + VkXYColorEXT_y, fl(0.06))
   Vk.put_i32(md, VkHdrMetadataEXT_whitePoint + VkXYColorEXT_x, fl(0.3127));  Vk.put_i32(md, VkHdrMetadataEXT_whitePoint + VkXYColorEXT_y, fl(0.3290))
-  Vk.put_i32(md, VkHdrMetadataEXT_maxLuminance, fi(1000))
+  Vk.put_i32(md, VkHdrMetadataEXT_maxLuminance, r3d_hdr_peak_nits())
   Vk.put_i32(md, VkHdrMetadataEXT_minLuminance, fl(0.001))
-  Vk.put_i32(md, VkHdrMetadataEXT_maxContentLightLevel, fi(1000))
-  Vk.put_i32(md, VkHdrMetadataEXT_maxFrameAverageLightLevel, fi(200))
+  Vk.put_i32(md, VkHdrMetadataEXT_maxContentLightLevel, r3d_hdr_peak_nits())
+  Vk.put_i32(md, VkHdrMetadataEXT_maxFrameAverageLightLevel, r3d_hdr_paper_nits())
   let chains = bytes(8)
   Vk.put_i64(chains, 0, gvk_swap)
   Vk.set_hdr_metadata_ext(gvk_dev, 1, chains, md)
diff --git a/packages/ludic.render3d/overlay.ludic b/packages/ludic.render3d/overlay.ludic
index a76ccf71..f5e4d9a3 100644
--- a/packages/ludic.render3d/overlay.ludic
+++ b/packages/ludic.render3d/overlay.ludic
@@ -53,10 +53,40 @@ var ov_clip_y: int = 0
 var ov_clip_w: int = 0
 var ov_clip_h: int = 0
 
+# The interface is sRGB. While the output is HDR10 the overlay draws with its HDR10 variant, which puts
+# the interface at the picture's paper white; the SDR program there sent sRGB values as PQ, and the
+# menu's yellow read as red on an HDR display.
+var ov_prog_sdr: int = 0
+var ov_prog_hdr: int = 0
+# How bright the interface's white is while HDR10 is on, as a multiple of paper white. It is 1 for the
+# interface; a calibration screen draws its test patches at a number of nits with ov_hdr_nits, which
+# closes the batch so far - the multiple is one uniform per flush. On an SDR frame it does nothing.
+var ov_hdr_scale: int = 0             # float bits; 0 until ov_begin sets 1
+function ov_hdr_nits(nits: int) -> void {
+  var s = F_ONE
+  if nits != 0 { s = f_div(nits, r3d_hdr_paper_nits()) }
+  if s == ov_hdr_scale { return }
+  if ov_open { ov_flush() }
+  ov_hdr_scale = s
+}
+# back to the interface's own white
+function ov_hdr_paper() -> void { ov_hdr_nits(0) }
+function ov_pick_prog() -> void {
+  if gpu_hdr_active() {
+    if ov_prog_hdr == 0 {
+      r3d_program_log("overlay.vert", "overlay.frag", "#define HDR10\n")
+      ov_prog_hdr = gpu_program("#version 410 core\n#define HDR10\n" + r3d_shader_file("overlay.vert"), "#version 410 core\n#define HDR10\n" + r3d_shader_file("overlay.frag"), "overlay.vert", "overlay.frag", "#define HDR10\n")
+    }
+    if ov_prog_hdr != 0 { ov_prog = ov_prog_hdr;  return }
+  }
+  ov_prog = ov_prog_sdr
+}
+
 function overlay_init(font_dir: string) -> bool {
   r3d_program_log("overlay.vert", "overlay.frag", "")
   ov_prog = gpu_program("#version 410 core\n" + r3d_shader_file("overlay.vert"), "#version 410 core\n" + r3d_shader_file("overlay.frag"), "overlay.vert", "overlay.frag", "")
   if ov_prog == 0 { print("overlay: program failed");  return false }
+  ov_prog_sdr = ov_prog
   ov_mesh = gpu_mesh_new()
   ov_vbo = gpu_mesh_vertices(ov_mesh, null, gl_bytes_of(OV_MAX_QUADS * 6 * OV_FLOATS), GPU_DYNAMIC)
   gpu_mesh_attr(ov_mesh, 0, 2, GPU_F32, OV_FLOATS * 4, 0, false)
@@ -163,12 +193,14 @@ function ov_begin() -> void {
   gpu_cull(false)
   gpu_blend(true)
   gpu_blend_func(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA)
+  ov_pick_prog()
   gpu_use_program(ov_prog)
   u_f2(gpu_uniform(ov_prog, "u_screen"), fi(gl_w), fi(gl_h))
   ov_n = 0;  ov_nr = 0;  ov_range_start = 0
   ov_tex = ov_white
   ov_mode = 2;  ov_voff = fi(8)
   ov_clip_w = 0
+  ov_hdr_scale = F_ONE
   ov_open = true
 }
 # everything drawn until ov_unclip stays inside this rectangle (a scrolling list)
@@ -198,12 +230,17 @@ function ov_flush() -> void {
   # framebuffer operation. Saying the target at each flush is what a render pass says anyway.
   gpu_fb_bind(gpu_screen_fb())
   gpu_viewport(0, 0, gl_w, gl_h)
+  ov_pick_prog()
   gpu_use_program(ov_prog)
   gpu_mesh_bind(ov_mesh)
   gpu_buffer_upload(ov_vbo, gl_bytes_of(ov_n * 6 * OV_FLOATS), ov_buf, GPU_STREAM)
   var font = ov_font
   if font == 0 { font = ov_white }
   r3d_bind_2d(ov_prog, "u_font", 1, font)
+  var hs = ov_hdr_scale
+  if hs == 0 { hs = F_ONE }
+  u_f(gpu_uniform(ov_prog, "u_hdr_paper"), r3d_hdr_paper_nits())
+  u_f(gpu_uniform(ov_prog, "u_hdr_scale"), hs)
   var last = -1
   var clipped = false
   for i in 0 .. ov_nr {
diff --git a/packages/ludic.render3d/post.ludic b/packages/ludic.render3d/post.ludic
index e32c925d..8b6aa6d1 100644
--- a/packages/ludic.render3d/post.ludic
+++ b/packages/ludic.render3d/post.ludic
@@ -327,6 +327,10 @@ function post_tonemap(color_tex: int) -> void {
   u_f3(gpu_uniform(prog, "u_wb"), fl(1.02), F_ONE, fl(0.97))
   u_f3(gpu_uniform(prog, "u_lift"), fl(0.004), fl(0.004), fl(0.012))
   u_f3(gpu_uniform(prog, "u_gain"), fl(0.99), fl(0.995), fl(1.0))
+  # the HDR10 variant's display calibration (the SDR program has none of these, and -1 sets nothing)
+  u_f(gpu_uniform(prog, "u_hdr_peak"), r3d_hdr_peak_nits())
+  u_f(gpu_uniform(prog, "u_hdr_paper"), r3d_hdr_paper_nits())
+  u_f(gpu_uniform(prog, "u_hdr_black"), r3d_hdr_black_nits())
   mesh_draw(post_fs)
   # sharpen + grain onto the screen
   gpu_fb_bind(gpu_screen_fb())
diff --git a/packages/ludic.render3d/shaders/overlay.frag b/packages/ludic.render3d/shaders/overlay.frag
index 070dabce..1b3d08f9 100644
--- a/packages/ludic.render3d/shaders/overlay.frag
+++ b/packages/ludic.render3d/shaders/overlay.frag
@@ -7,8 +7,11 @@ uniform sampler2D u_tex;
 uniform sampler2D u_font;
 out vec4 o_color;
 #ifdef HDR10
-// the interface is sRGB: drawn into an HDR10 frame it sits at paper white, as the picture's white does
-const float HDR_PAPER = 200.0;
+// the interface is sRGB: drawn into an HDR10 frame its white sits at the player's paper white, as the
+// picture's white does. u_hdr_scale multiplies that for one batch (ov_hdr_nits): a calibration
+// screen's test patches, which have to reach past paper white to the display's peak.
+uniform float u_hdr_paper;
+uniform float u_hdr_scale;
 vec3 bt709_to_2020(vec3 c) {
   return mat3(0.6274, 0.0691, 0.0164, 0.3293, 0.9195, 0.0880, 0.0433, 0.0114, 0.8956) * c;
 }
@@ -30,6 +33,7 @@ void main() {
     o_color = vec4(v_col.rgb * t.rgb, v_col.a * t.a);
   }
 #ifdef HDR10
-  o_color.rgb = pq_encode(bt709_to_2020(pow(max(o_color.rgb, vec3(0.0)), vec3(2.2))) * HDR_PAPER);
+  float nits = max(u_hdr_paper, 80.0) * max(u_hdr_scale, 0.0);
+  o_color.rgb = pq_encode(bt709_to_2020(pow(max(o_color.rgb, vec3(0.0)), vec3(2.2))) * nits);
 #endif
 }
diff --git a/packages/ludic.render3d/shaders/spv/a4683767.frag.spv b/packages/ludic.render3d/shaders/spv/a4683767.frag.spv
index 00a755fa..2ecfde12 100644
Binary files a/packages/ludic.render3d/shaders/spv/a4683767.frag.spv and b/packages/ludic.render3d/shaders/spv/a4683767.frag.spv differ
diff --git a/packages/ludic.render3d/shaders/spv/e86f78e8.frag.spv b/packages/ludic.render3d/shaders/spv/e86f78e8.frag.spv
index 24e28a71..91f127f8 100644
Binary files a/packages/ludic.render3d/shaders/spv/e86f78e8.frag.spv and b/packages/ludic.render3d/shaders/spv/e86f78e8.frag.spv differ
diff --git a/packages/ludic.render3d/shaders/spv/manifest.txt b/packages/ludic.render3d/shaders/spv/manifest.txt
index fcc70708..a76f578e 100644
--- a/packages/ludic.render3d/shaders/spv/manifest.txt
+++ b/packages/ludic.render3d/shaders/spv/manifest.txt
@@ -578,7 +578,7 @@ T 725523d9 u_shadow 9
 T 725523d9 u_tershadow 10
 T 725523d9 u_ts_height 11
 P a4683767 fullscreen.vert tonemap.frag #define HDR10;
-B a4683767 frag 1 852
+B a4683767 frag 1 864
 U a4683767 frag u_cascade_vp 0 mat4 5 64
 U a4683767 frag u_cascade_split 320 float 5 16
 U a4683767 frag u_cascade_range 400 float 5 16
@@ -618,6 +618,9 @@ U a4683767 frag u_bloom_strength 836 float 1 0
 U a4683767 frag u_vignette 840 float 1 0
 U a4683767 frag u_saturation 844 float 1 0
 U a4683767 frag u_contrast 848 float 1 0
+U a4683767 frag u_hdr_paper 852 float 1 0
+U a4683767 frag u_hdr_peak 856 float 1 0
+U a4683767 frag u_hdr_black 860 float 1 0
 T a4683767 u_adapt 2
 T a4683767 u_ao 3
 T a4683767 u_bloom 4
@@ -1932,7 +1935,7 @@ U e86f78e8 vert u_screen 0 vec2 1 0
 I e86f78e8 a_pos 0 vec2
 I e86f78e8 a_uv 1 vec2
 I e86f78e8 a_col 2 vec4
-B e86f78e8 frag 0 764
+B e86f78e8 frag 1 772
 U e86f78e8 frag u_cascade_vp 0 mat4 5 64
 U e86f78e8 frag u_cascade_split 320 float 5 16
 U e86f78e8 frag u_cascade_range 400 float 5 16
@@ -1961,6 +1964,8 @@ U e86f78e8 frag u_ts_on 748 float 1 0
 U e86f78e8 frag u_force_cascade 752 int 1 0
 U e86f78e8 frag u_cloud_shadow 756 float 1 0
 U e86f78e8 frag u_time 760 float 1 0
+U e86f78e8 frag u_hdr_paper 764 float 1 0
+U e86f78e8 frag u_hdr_scale 768 float 1 0
 T e86f78e8 u_brdf 2
 T e86f78e8 u_font 3
 T e86f78e8 u_irradiance 4
diff --git a/packages/ludic.render3d/shaders/tonemap.frag b/packages/ludic.render3d/shaders/tonemap.frag
index dac0127a..cf11f5ca 100644
--- a/packages/ludic.render3d/shaders/tonemap.frag
+++ b/packages/ludic.render3d/shaders/tonemap.frag
@@ -22,9 +22,11 @@ vec3 aces(vec3 x) {
 }
 float hash(vec2 p) { return fract(sin(dot(p, vec2(12.9898, 78.233))) * 43758.5453); }
 #ifdef HDR10
-// HDR10 output: nits in BT.2020 primaries, encoded with the SMPTE ST 2084 (PQ) curve
-const float HDR_PAPER = 200.0;   // nits the SDR picture's white sits at
-const float HDR_PEAK = 1000.0;   // nits the brightest highlight rolls on to
+// HDR10 output: nits in BT.2020 primaries, encoded with the SMPTE ST 2084 (PQ) curve. The three
+// numbers are the player's calibration of their display (r3d_hdr_calibrate).
+uniform float u_hdr_paper;        // nits the SDR picture's white sits at
+uniform float u_hdr_peak;         // nits the brightest highlight rolls on to: what the display reaches
+uniform float u_hdr_black;        // nits the darkest shade is lifted to, fading out toward paper white
 vec3 bt709_to_2020(vec3 c) {
   return mat3(0.6274, 0.0691, 0.0164, 0.3293, 0.9195, 0.0880, 0.0433, 0.0114, 0.8956) * c;
 }
@@ -57,9 +59,16 @@ void main() {
   float vig = 1.0 - u_vignette * dot(q, q) * 0.5;
   c *= vig;
 #ifdef HDR10
-  // up to paper white the SDR picture as it is; past it, what ACES clipped runs on to the peak
-  vec3 hi = max(pre - 1.0, vec3(0.0));
-  vec3 nits = (c + hi / (hi + 1.0) * (HDR_PEAK / HDR_PAPER - 1.0) * vig) * HDR_PAPER;
+  // up to paper white the SDR picture as it is; past it, the whole graded colour is brightened by one
+  // factor from its brightest channel. Extending each channel on its own boosted a bright yellow's red
+  // far more than its green, and yellow read as red on an HDR display.
+  float paper = max(u_hdr_paper, 80.0);
+  float peak = max(u_hdr_peak, paper);
+  float over = max(max(pre.r, max(pre.g, pre.b)) - 1.0, 0.0);
+  float lift = 1.0 + over / (over + 1.0) * (peak / paper - 1.0);
+  vec3 nits = c * lift * paper;
+  // the black level: the shadows' floor raised for a display that crushes them, gone by paper white
+  nits += max(u_hdr_black, 0.0) * (1.0 - clamp(nits / paper, 0.0, 1.0));
   vec3 e = pq_encode(bt709_to_2020(nits));
   e += (hash(gl_FragCoord.xy) - 0.5) / 1023.0;
   o_color = vec4(e, 1.0);