Albedo to Normal and MER for Blockbench

PBR channels are derived, not painted: albedo → height field → tangent-space normal, then metalness, emissive and roughness inferred from the albedo, the height and the normal's curvature and packed into one MER image. Two scripts share one CLI and the same maths; pick by runtime. Load blockbench-use first for discovery and verification, and blockbench-pbr-materials to assign the results. This skill produces the image files only.

Both write <name>_height.png (grayscale, light = high), <name>_normal.png (RGB, opaque) and <name>_mer.png (R metalness, G emissive, B roughness) and print a JSON report. Runtime setup, API notes and troubleshooting: references/python-pypbr.md, references/node-vgpu.md. Node needs the script's scripts/ folder reachable from a project that has the dependencies installed; Python only needs the packages.

Workflow

1. Get the color texture as a file

Run list_textures and note the target texture's UUID, bitmap_size and uv_size; it does not report a file path. If the texture was imported from a file you wrote (for example the downscaled atlas from the GPT image workflow), use that file. Otherwise fetch the image with get_texture and save the returned PNG to disk, or have Blockbench save the texture. Work on the atlas at its native texel size, not on an upscaled generation canvas, so the maps share the texel grid with the color map.

Check the atlas before deriving anything: relief scale must be consistent across faces, so apply UV scale and distortion guidance to the color map first. A normal map inherits every stretch in the UV layout.

2. Choose the height source

Depth estimation sees a photo, not a tile: it returns a foreground-to-background ramp that breaks tiling. The script keeps --flatten 1 and normalize on for depth; add --high-pass <texels> (about a quarter of the tile width) for non-linear bias and --seam offset for seamless tiles. Small textures are nearest-neighbour upscaled to at least 1024 px before the model and block-averaged back, so 16× art keeps its edges. Details: references/height-processing.md.

3. Run

# tiling 16x block, pronounced pixel relief
python scripts/albedo_to_normal.py block.png --out ./pbr --wrap --strength 1
node   scripts/albedo_to_normal.mjs block.png --out ./pbr --wrap --strength 1

# entity/prop atlas with transparent gutters (islands isolated automatically)
python scripts/albedo_to_normal.py goal_atlas.png --out ./pbr --strength 0.5

# HD tile from a painterly texture, depth-estimated, softened for smooth relief
node scripts/albedo_to_normal.mjs planks.png --out ./pbr --height-source depth --high-pass 32 --seam offset --wrap --soften 1

MER inference is heuristic. Read references/mer-inference.md before tuning it: bright desaturated colours read as metal and bright saturated colours read as glow, which is wrong for wool, bone, snow, pale skin, yellow beaks and painted signs. Decide the material first, then choose auto, a uniform value or palette overrides per channel.

4. Read the report

The JSON on stdout ends with report and merReport. For the normal, require verdict: "ok" and classification: "standard"; meanXYBias near 0 and negativeZCount 0. A heightfield classification means the albedo argument was a grayscale image; warn with a large bias on a tile means an unflattened ramp in the height. flatPct is informational (high on flat art and on atlases with big gutters).

For the MER, compare metalPct and emissivePct with what the material actually is, and roughnessMean with how matte it should look. A wooden crate with metalPct 0.4 means the pale planks were misread as steel: rerun with --metal 0 or a palette. paletteTexels 0 with a palette means the colour did not match exactly. The report says the encodings are sound, not that the relief direction, scale or material assignments are right; that is step 6.

5. Import and assign in Blockbench

create_texture: name="<name>_normal", data="<absolute path to <name>_normal.png>"
create_texture: name="<name>_mer",    data="<absolute path to <name>_mer.png>"
create_pbr_material: name="<material>", color_texture="<albedo>", normal_texture="<name>_normal", mer_texture="<name>_mer"
# or on an existing material:
assign_texture_channel: material="<material>", texture="<name>_normal", channel="normal"
assign_texture_channel: material="<material>", texture="<name>_mer", channel="mer"
get_material_info: material="<material>"

Bedrock texture sets take normal or heightmap, never both. Assign the _height.png as height_texture instead when the target is 16× vanilla-style pixel art and the pack convention prefers heightmaps; otherwise use the normal. A MER texture requires the color texture on the same material; when the whole surface shares one metal/emissive/roughness value, mer_value on the material is simpler than a map (generate with --no-mer). Match uv_width/uv_height on create_texture to the color texture in formats with per-texture UV sizes. Channel rules, uniform MER values and save_material_config are in blockbench-pbr-materials.

6. Verify direction and scale

Look at the lit model with capture_screenshot from at least two angles and at the intended viewing distance:

• Raised features must read as raised. Inverted top-to-bottom shading means the wrong green convention: regenerate with the other --convention. Everything reading inverted (pits as bumps) means the height sense is wrong: regenerate with --invert-height.
• Relief must look the same size on every face. Adjust --strength globally; fix uneven results in the UV layout or the color atlas, not by hand-editing the normal.
• Tiling blocks: place several copies and check the seams; --wrap and --seam offset on the height are the fixes, not painting over the seam.
• No rim around atlas islands. If one appears, the albedo alpha was not clean; raise --alpha-threshold or clean the gutters and regenerate.
• Metal regions must be the parts that are metal (they turn dark and reflective under RTX), glow must sit only on light sources, and roughness must not make cloth or paint shiny. Fix with uniform values, palette overrides or the roughness terms, and regenerate the MER rather than painting it.
• The rendered preview only proves Blockbench's shading; confirm in the target game or renderer before delivery.

What to expect

• Luminance height is an artistic proxy: painted highlights become bumps and painted shadows become pits. It is the right choice for stylised and pixel art, and wrong for photo-sourced textures.
• Depth estimation on textures is relief-plausible, not measured. Expect per-run variation between the PyTorch and ONNX model conversions and treat --flatten / --high-pass / --seam as required cleanup for tiles.
• Both runtimes produce byte-identical heights from the same luminance input, normals within two levels of each other from the same height, and MER within three levels on roughness with identical metal masks.
• MER inference is colour and shape heuristics, not material recognition. Expect false metal on pale desaturated areas and false glow on bright saturated ones; the report makes both visible and the overrides fix them without painting.
• PyPBR's own compute_normal_from_height (0.1.0b5) zero-pads borders and flips X, so the Python script derives the normal itself and uses PyPBR for the material object, folder I/O and follow-up operations.
• Node resolves vgpu, pngjs and the shaders from the script's location; without a GPU, run npx vgpu install-software-renderer once and pass --gpu software.

Resources

• references/height-processing.md: the height and normal pipeline stage by stage, depth shaping, kernel maths, conventions, report fields, runtime parity.
• references/mer-inference.md: how metalness, emissive and roughness are inferred, every MER flag, overrides, the MER report and the checks to run.
• references/python-pypbr.md: install, PyPBR material API and quirks, Depth Anything through transformers.
• references/node-vgpu.md: install, vgpu compute/texture API used by the script, WGSL notes, transformers.js depth in Node.
• scripts/albedo_to_normal.py: Python pipeline (torch + PyPBR, optional transformers).
• scripts/albedo_to_normal.mjs: Node pipeline (vgpu + Dawn, pngjs, optional transformers.js).
• scripts/shaders/height-map.wgsl, normal-map.wgsl, mer-map.wgsl: the GPU passes; also readable as the reference maths.