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Upscaling for large format print - results and pitfalls

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(@davidh)
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Joined: 1 week ago
Posts: 142
Topic starter   [#18625]

A recent project required generating high-resolution artwork for large-format exhibition printing, pushing the boundaries of AI upscaling tools. The primary requirement was a final output of 120cm x 80cm at 150 DPI, which translates to a pixel dimension of approximately 7087 x 4724 (or ~33.5 megapixels). Starting from a standard Leonardo.ai canvas generation (typically 1024x1024 or similar), this necessitates a significant upscale factor, far beyond simple pixel doubling.

I conducted a comparative analysis of the available upscaling methods within Leonardo.ai, specifically focusing on the "AI Upscaler" options and their interaction with the platform's native "Alchemy" and "Prompt Magic" refinements. The goal was to quantify the trade-offs between detail generation, introduction of artifacts, and processing time. My workflow and findings are summarized below.

**Methodology & Comparative Results**

1. **Baseline Generation:** All tests originated from a single base image generated with Alchemy V2 (Refined) and Prompt Magic set to High. Resolution was 1024x1408, a common starting point for portrait-oriented pieces.
2. **Upscaling Pathways Tested:**
* **Method A:** Direct application of "Creative Upscale" (4x) on the base image.
* **Method B:** Two-step process: First, "General Upscale" (2x), followed by a second "General Upscale" (2x) on the intermediate result.
* **Method C:** "General Upscale" (2x) on the base image, followed by exporting the intermediate and using a dedicated external upscaling tool (Topaz Gigapixel AI) for the final 4x target.
* **Method D:** Using Leonardo's "Image2Image" at a higher resolution with a very low strength (0.2) and the original prompt, attempting to guide a re-generation at larger scale.

**Key Observations & Pitfalls**

* **Artifact Introduction:** The "Creative Upscale" (Method A) consistently introduced novel, undesirable textures in large, flat areas of the image (e.g., a smooth sky gradient developed a fibrous, cloth-like pattern). This is the most critical pitfall for print media, where such artifacts become glaringly obvious at close viewing distances.
* **Detail Hallucination:** While "Creative Upscale" added impressive detail to textured areas (foliage, stonework), the hallucinated details were not always coherent upon close inspection. "General Upscale" (Method B) was more conservative, but resulted in a perceptibly softer final image when viewed at 100%.
* **Resource Cost & Time:** The two-step internal upscaling (Method B) consumed significantly more tokens per operation than a single 4x upscale. The external software approach (Method C) yielded the highest subjective detail retention but obviously adds cost and step complexity outside the Leonardo ecosystem.
* **Resolution Limits:** A fundamental pitfall is hitting the platform's maximum output resolution cap (currently 2048x2048 in many modes, 3072x3072 with upscaling). This makes the native generation of a ~7000px image impossible in a single step, forcing a multi-stage workflow with potential generational loss.

**Optimal Workflow Derived**

Based on repeated tests, the most reliable workflow for my print-quality requirement was:

1. Generate the best possible base image with Alchemy and high Prompt Magic.
2. Perform an initial 2x "General Upscale" within Leonardo.ai. This provides a clean, artifact-minimized intermediate.
3. Export the 2x upscaled image and process it through a dedicated, offline upscaling engine (like Topaz Gigapixel AI or ESRGAN-based models) configured for photographic realism. This software is specifically tuned for this final step and offers more control over sharpening and artifact suppression.
4. Conduct a final manual inspection at 100% zoom for repeating patterns, smudging, or aberrant textures, particularly in smooth gradient areas.

The core conclusion is that while Leonardo.ai's upscalers are excellent for digital display and moderate enlargement, their stochastic nature can introduce print-critical artifacts. For large-format physical output, a hybrid approach leveraging Leonardo for the creative generation and initial scale, followed by a deterministic, fine-tuned external tool for the final enlargement, produced superior results. The community's insights on alternative multi-step prompting or fine-tuned models for upscaling within the platform would be highly valuable.


Data over dogma


   
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