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# PNG rendering error troubleshooting (2025-11-01 15:48Z)

_**User (2025-11-01 15:48Z)**_

why is this happening to render


libpng error: IDAT: CRC error

ImageInput::read_image() failed: PNG read error: IDAT: CRC error

PNG library error

IMB_load_image_from_memory: unknown file-format (R:\Creative\artsy\maya\2025-02 BondingArtifact\Renders\3_background\2025-10-26\3_background_dark\3_background_dark_5489.png)

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_**Agent (model default, mode Agent)**_


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Reviewing the open file to understand the render configuration and identify why PNGs are being corrupted.


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<tool-use data-tool-type="read" data-tool-name="read_file">
<details><summary>Tool use: **read_file** • Read file: c:\Program Files\Blender Foundation\Flamenco 3.7\scripts\TalkingHeads cycles_optix_gpu_NOBAT.js</summary>

</details>
</tool-use>

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<tool-use data-tool-type="search" data-tool-name="codebase_search">
<details>
                <summary>Tool use: **codebase_search** • Searched codebase "How are PNG images saved or written during rendering?" • **3** results</summary>
            
| File | Lines |
|------|-------|
| `.gitignore` | L134 |
| `.gitattributes` | L47 |
| `misc/checklist.txt` | L52 |

</details>
</tool-use>

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Checking the render configuration and the corrupt file path for clues.


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<tool-use data-tool-type="search" data-tool-name="codebase_search">
<details>
                <summary>Tool use: **codebase_search** • Searched codebase "Where are render output files written or saved?" • **10** results</summary>
            
| File | Lines |
|------|-------|
| `.gitignore` | L134 |
| `assets/Objects/gems/tx/BlackOnyx/Designer/BlackOnyx.sbs` | L3573-3642 |
| `misc/checklist.txt` | L52 |
| `misc/metadata.bat` | L23 |
| `misc/filenames.bat` | L1 |
| `.cursorindexingignore` | L3 |
| `.gitattributes` | L47 |
| `assets/Objects/gems/tx/BlackOnyx/Designer/BlackOnyx.sbs` | L1475-1533 |
| `misc/BRANDING.txt` | L2 |
| `assets/Objects/gems/tx/BlackOnyx/Designer/BlackOnyx.sbs` | L1976-2034 |

</details>
</tool-use>

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<tool-use data-tool-type="grep" data-tool-name="grep">
<details>
<summary>Tool use: **grep** • Grep for "3_background" • 0 matches</summary>

Output mode: content


_No matches found_

</details>
</tool-use>

---


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This PNG CRC error indicates the file was corrupted during render. The path `R:\...` suggests a network drive, which is a common source.

Common causes:
- Network storage issues: timeouts, interruptions, or bad connections corrupt writes
- Concurrent access: another process (comp, preview, antivirus) reading while a worker writes
- Incomplete writes: file read before the write finishes
- Antivirus/backup: scanning or copying files while they’re being written

Checking the render script for timing or synchronization issues:


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<tool-use data-tool-type="read" data-tool-name="read_file">
<details><summary>Tool use: **read_file** • Read file: c:\Program Files\Blender Foundation\Flamenco 3.7\scripts\TalkingHeads cycles_optix_gpu_NOBAT.js</summary>

</details>
</tool-use>

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## Solutions to fix this:

### **Immediate fixes:**

1. **Check if the file is actually corrupted**
   - Verify frame `5489` on the R: drive
   - If corrupted, re-render just that frame

2. **Render to local storage first, then copy**
   - Change the render output to a local drive (C: or D:)
   - After rendering completes, copy to the network drive
   - Reduces corruption risk from network interruptions

3. **Increase chunk_size**
   - In your Flamenco job settings, increase `chunk_size` (currently defaults to 1)
   - Fewer concurrent writes = less contention

4. **Temporarily disable antivirus/backup scanning**
   - Exclude the render output folder from real-time scanning
   - Network drives are often scanned aggressively

### **Network storage specific:**

5. **Check network drive health**
   - Test the R: drive connection stability
   - Run `chkdsk R: /f` if it's accessible
   - Check for network timeouts or packet loss

6. **Add file write delay/sync**
   - If possible, configure Blender to flush writes completely before finishing
   - Use `--python-expr` to add a small delay after rendering completes

### **For the current corrupted frame:**

The file `3_background_dark_5489.png` is corrupted. Either:
- Re-render frame 5489 specifically, or
- Skip it and continue (if it's not critical)

Should I help modify the Flamenco script to render to a local directory first, or focus on diagnosing the network storage issue?

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_**User (2025-11-02 23:49Z)**_

How do I ensure my image can be denoised without rendering in future? Can saving as EXR fix it?

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_**Agent (model default, mode Agent)**_


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Checking how denoising and output formats are configured. Reviewing the render script for format/pass options and searching the codebase for denoising-related settings.


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<tool-use data-tool-type="search" data-tool-name="codebase_search">
<details>
                <summary>Tool use: **codebase_search** • Searched codebase "How are denoising passes or denoising data configured for rendering?" • **7** results</summary>
            
| File | Lines |
|------|-------|
| `misc/checklist.txt` | L52 |
| `assets/Objects/gems/tx/BlackOnyx/Designer/BlackOnyx.sbs` | L3573-3642 |
| `.gitignore` | L134 |
| `assets/Objects/gems/tx/BlackOnyx/Designer/BlackOnyx.sbs` | L1431-1479 |
| `assets/Objects/gems/tx/BlackOnyx/Designer/BlackOnyx.sbs` | L73 |
| `.gitattributes` | L47 |
| `assets/Objects/gems/tx/BlackOnyx/Designer/BlackOnyx.sbs` | L1858-1925 |

</details>
</tool-use>

---

<tool-use data-tool-type="grep" data-tool-name="grep">
<details>
<summary>Tool use: **grep** • Grep for "denois" • 0 matches</summary>

Output mode: content


_No matches found_

</details>
</tool-use>

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<tool-use data-tool-type="grep" data-tool-name="grep">
<details>
<summary>Tool use: **grep** • Grep for "EXR|exr|OpenEXR" • 0 matches</summary>

Output mode: content


_No matches found_

</details>
</tool-use>

---


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EXR can enable post-render denoising, but you need to enable the denoising passes when rendering.

- EXR stores multiple passes/layers in one file (denoising data, beauty, etc.)
- EXR stores 32-bit float data (vs 8-bit PNG), preserving detail
- PNG cannot store denoising passes, so denoising later isn't possible

Updating the render script to automatically enable denoising passes when EXR is selected:


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<tool-use data-tool-type="read" data-tool-name="read_file">
<details><summary>Tool use: **read_file** • Read file: c:\Program Files\Blender Foundation\Flamenco 3.7\scripts\TalkingHeads cycles_optix_gpu_NOBAT.js</summary>

</details>
</tool-use>

---


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Adding code to automatically enable denoising passes when rendering to EXR:


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<tool-use data-tool-type="read" data-tool-name="read_file">
<details><summary>Tool use: **read_file** • Read file: c:\Program Files\Blender Foundation\Flamenco 3.7\scripts\TalkingHeads cycles_optix_gpu_NOBAT.js</summary>

</details>
</tool-use>

---

<tool-use data-tool-type="write" data-tool-name="search_replace">

<details><summary>Tool use: **code_edit** • Edit file: c:\Program Files\Blender Foundation\Flamenco 3.7\scripts\TalkingHeads cycles_optix_gpu_NOBAT.js</summary>

</details>

</tool-use>

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_**User (2025-11-02 23:49Z)**_

Don't edit anything. just tell me what I should set my render settings to.

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_**Agent (model default, mode Agent)**_


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Here’s what to set in Blender so you can denoise later:

## Render settings

### 1. Output format
- Output Properties tab → Output section
- Set File Format to OpenEXR or OpenEXR Multilayer
- OpenEXR Multilayer is better if you need multiple passes later

### 2. Enable denoising passes
- Output Properties tab → View Layer Properties → Passes section
- Enable:
  - Denoising Normal
  - Denoising Albedo
  - Denoising Shadow (optional, helps quality)

### 3. Cycles denoising (during render)
- Render Properties tab → Denoising section
- Denoiser: OpenImageDenoise (or OptiX if on NVIDIA)
- Enable Denoising
- If using Passes → Data:
  - Enable Normal
  - Enable Albedo (optional if not using denoising passes)

### 4. Render passes to save
- View Layer Properties → Passes → Data:
  - Enable Normal
  - Enable Albedo (if you want them as separate passes)
- With OpenEXR Multilayer, passes are stored as layers in the file

## Why this works

- EXR stores all passes in one file
- 32-bit float preserves detail
- Denoising Normal/Albedo passes let you re-denoise later
- You can denoise post-render in Compositor or with external tools

## After rendering

You can re-denoise later:
- In Blender Compositor: load the EXR, use Denoise node with the passes
- Or keep render denoising off during render and denoise entirely in post

Note: PNG cannot store denoising passes, so you can’t re-denoise PNG renders later. EXR is required for this workflow.

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_**User (2025-11-02 23:49Z)**_

So, when I send to sheepit, denoising will be disabled if I use the tiling option (which splits the frame into 2x2, 3x3, 4x4, or 6x6 so multiple workers can render one frame simultaneously, then they are combined) but I need to denoise it because the results are so noisy.

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_**Agent (model default, mode Agent)**_


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For SheepIt with tiling, you can't denoise during rendering (denoising needs the full frame), but you can denoise the combined EXR frames afterward if you save the required passes.

## Render settings for SheepIt + tiling

### 1. Output format
- File Format: OpenEXR Multilayer (or OpenEXR)
- Required so denoising passes are saved per tile and combined

### 2. View Layer passes (critical)
- View Layer Properties → Passes → Data:
  - Enable Denoising Normal
  - Enable Denoising Albedo
  - Enable Denoising Shadow (recommended)
- View Layer Properties → Passes → Combined:
  - Enable Denoising Data (if available; some versions)

### 3. Cycles render settings
- Render Properties → Denoising:
  - Denoiser: OpenImageDenoise (or OptiX if available)
  - Keep Denoising enabled in settings
- Note: With tiling, denoising won't run during render, but passes will still be saved.

### 4. After SheepIt combines tiles
You'll have EXR files with:
- Combined beauty pass (noisy)
- Denoising Normal pass
- Denoising Albedo pass
- Denoising Shadow pass (if enabled)

## Denoise the combined frames

### Option A: Blender Compositor
1. Open a combined EXR in Image Editor or Compositor
2. Use Denoise node:
   - Connect Combined (beauty)
   - Connect Denoising Normal
   - Connect Denoising Albedo
   - Optionally connect Denoising Shadow
3. Export the denoised result

### Option B: External tools
- OIDN (OpenImageDenoise CLI)
- GIMP (with EXR support)
- Natron or other compositing software

## Summary
- Render EXR with Denoising Normal, Denoising Albedo (and Shadow if available)
- Tiles will combine these passes into full-frame EXRs
- Denoise the combined EXRs in post using those passes

This way you get fast tiled rendering on SheepIt and clean denoised results afterward.

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_**User (2025-11-03 07:09Z)**_

Ach, looks like I can't render splits. this makes splits kind of useless for me... so I can't send this blend with such high samples because it's so long that each machine doesn't get it, but if I split it, I'll just have to denoise it after anyway... is there a better solution for denoising than the compositing solution I devised?

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_**Agent (model default, mode Agent)**_


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Given SheepIt’s EXR restriction (no splits), here are practical alternatives:

## Option 1: Render with splits in PNG + enable render-time denoising
- Render to PNG (splits allowed)
- In Cycles: enable Denoising (OpenImageDenoise or OptiX)
- Denoising should run per tile during render
- Result: already denoised when tiles combine

Note: Verify that SheepIt/Blender doesn’t disable denoising with splits. Test a single split frame first.

## Option 2: Lower samples + better denoising (recommended)
Modern denoisers work well with fewer samples:
- Reduce samples (e.g., 128–256 instead of 1000+)
- Keep denoising enabled during render
- Render to PNG with splits enabled
- Benefits: faster renders, workers complete tasks, denoised output

## Option 3: AI denoisers that don’t need passes
If render-time denoising doesn’t work with splits, use standalone denoisers:
- Neat Video (plugin for Premiere/AE/Resolve)
- Topaz DeNoise AI
- Adobe Lightroom/Photoshop AI Denoise

Trade-off: No denoising passes needed, but single-pass input only.

## Option 4: Hybrid two-pass workflow
If you need high samples:
1. Pass 1: Render beauty only with splits (PNG), high samples
2. Pass 2: Render denoising passes (Normal/Albedo) full-frame, low samples, EXR
3. Composite: Combine passes in Blender Compositor and denoise

Downside: Two renders, more work.

## Recommendation
Try Option 1 first: PNG + splits + render-time denoising enabled. If that doesn’t work or quality isn’t enough, use Option 2 (lower samples + denoising). The quality difference with modern denoisers is often minimal, and render time drops significantly.

If you can share sample count and resolution, I can suggest specific settings.

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