Gemini 3 Pro Image Preview: softer vegetation / foliage detail degradation in 4K outputs, same behavior across apps

Gemini API
1

We are seeing a consistent quality degradation with gemini-3-pro-image-preview for real-estate image enhancement workflows.

The main issue is not overall resolution. The model is returning true 4K native PNG outputs, but foliage, bushes, and grass often look noticeably softer / blurrier / more painterly than before, while architecture remains relatively sharp.

What makes this notable:

  • Same source image
  • Same prompt
  • Same requested output size
  • Same model: gemini-3-pro-image-preview
  • Same behavior across two separate apps/integrations, including OpenArt and our own app

We initially suspected our pipeline, but our logging now confirms:

  • native output: image/png
  • final output: image/png
  • native size: 4800x3584
  • final size: 4800x3584

Example provider metadata from our app:

{
  "route": "/api/enhance",
  "provider": "gemini",
  "imageSize": "4K",
  "imageCount": 2,
  "modelsUsed": ["gemini-3-pro-image-preview"],
  "requestMode": "enhance",
  "fallbackUsed": false,
  "modelVersionsUsed": ["gemini-3-pro-image-preview"],
  "outputDiagnostics": [
    {
      "index": 0,
      "modelUsed": "gemini-3-pro-image-preview",
      "responseId": "2FL-afiiEKb_lOoPvPnW6QY",
      "modelVersion": "gemini-3-pro-image-preview",
      "nativeOutputWidth": 4800,
      "nativeOutputHeight": 3584,
      "requestedImageSize": "4K",
      "nativeOutputMimeType": "image/png",
      "normalizedOutputWidth": 4800,
      "normalizedOutputHeight": 3584,
      "normalizedOutputMimeType": "image/png"
    }
  ]
}
2

Hello @mikessian,
Can you share prompt details, model configuration, and a minimal code snippet to troubleshoot this issue?

3

Hi @Pooja_Kapse
The prompt is a request to convert a CGI image into a photorealistic one. Nothing too elaborate. In fact, I’ve tested several different prompts to get the same result, and the issue persists with all of them, so I’m pretty sure the prompt is not the problem.

Everything was working perfectly until 05/07/2026, when I started noticing a clear quality drop in 4K generations. Strangely, the 2K generations look better, although obviously at a lower resolution.

I got these results in my own app, using the Gemini 3 Pro Image Preview API key through Vertex. I also got the same results directly in the Vertex platform, and even on well-known sites like OpenArt — which I assume are also using Vertex for their API.

Before the date when the issue started, everything was working perfectly.

There isn’t really a code error I can share. This seems to be an issue with the 4K images currently being returned by this generation model.

4

Time Stamp; looks like the issue was fixed today.