Persistent quality regression: distortion and magenta tint in Gemini 3 Pro 4K (Vertex AI)

Gemini API
, , ,
1

Hi everyone,

I’m reporting a critical and persistent issue when generating and editing images with Gemini 3 Pro via the Vertex AI or Google Cloud API.

The Problem:

Following its launch in November 2025, the model produced excellent results. However, since late February 2026 (coinciding with the release of Gemini 3.1 / Nano Banana 2), the quality has degraded drastically despite using the exact same workflow and prompts.

The main symptoms are:

  1. Deformation: The model distorts shapes and proportions from the reference images.
  2. Cumulative magenta tint: A pinkish tone appears and worsens with each successive iteration or edit.
  3. Loss of micro-details: “Pasty” or plastic-looking textures that are unacceptable for high resolutions.

Environment:

  • API: Vertex AI
  • Model: gemini-3-pro-image-preview
  • Output Resolution: Always 4K

Project Constraint:

Our workflow demands maximum fidelity. We cannot migrate to the Gemini 3.1 family because its quality is noticeably lower for this use case. We depend on 3 Pro returning to its original quality.

Questions for the community:

  • Is anyone else experiencing this degradation specifically in 4K via Vertex AI?
  • Is there any known server capacity issue, an open official ticket, or any workaround to mitigate the distortion and magenta tint?
2

I’ve seen some magenta tint to dark colors but I find that its an exaggeration of tinting caused by the UV coating on a lens or polarizing filter. You may not notice it as much before giving it to Gemini but it will be exaggerated. Are you only noticing it on dark colors / black tones?

I’ve been unsuccessful at asking gemini to correct it and only replacing the content with more specific coloration details works. (Replace the mulch with dark matte charcoal black mulch).

3

In my experience, this issue consistently affects the entire image. It appears as though the initial rendering process prematurely applies a magenta tint to elements such as shirts and skin tones; furthermore, this distortion significantly alters the overall color profile of white backgrounds.

4

Hello All,
For issues related to the Vertex API, please contact your sales representative if you have one. Otherwise, you can find more relevant assistance on the Google Cloud Forum.