gemini-3-pro-image-preview (Image Edit) - GPTProto API Documentation

Authentication

Sign up for a GPTProto account at https://gptproto.com
Navigate to the API Keys section in your dashboard
Generate a new API key (sk-xxxxx)
Copy and securely store your API key For authentication details, please refer to the Authentication section.

Initiate Request

curl --location 'https://gptproto.com/v1beta/models/gemini-3-pro-image-preview:generateContent' \
--header 'Authorization: GPTPROTO_API_KEY' \
--header 'Content-Type: application/json' \
--data '{
  "contents": [
    {
      "role": "user",
      "parts": [
        {
          "text": "Put a hat on the cat"
        },
        {
          "fileData": {
            "mimeType": "image/png",
            "fileUri": "https://tos.gptproto.com/resource/cat.png"
          }
        }
      ]
    }
  ],
  "generationConfig": {
    "imageConfig": {
      "aspectRatio": "1:1",
      "imageSize": "4K"
    }
  }
}'

Response Example

{
  "candidates": [
    {
      "content": {
        "parts": [
          {
            "inlineData": {
              "mimeType": "image/jpeg",
              "data": "base64_encode_data"
            }
          }
        ],
        "role": "model"
      },
      "finishReason": "STOP",
      "index": 0
    }
  ],
  "usageMetadata": {
    "promptTokenCount": 7,
    "candidatesTokenCount": 1202,
    "totalTokenCount": 1347,
    "promptTokensDetails": [
      {
        "modality": "TEXT",
        "tokenCount": 7
      }
    ],
    "candidatesTokensDetails": [
      {
        "modality": "IMAGE",
        "tokenCount": 1120
      }
    ],
    "thoughtsTokenCount": 138
  },
  "modelVersion": "gemini-3-pro-image-preview",
  "responseId": "rUhKaeiQJceM-sAP5p7bsAo"
}

Parameters

Core Parameters

Parameter	Type	Required	Default	Range	Description
`contents`	array	✅ Yes	-	-	Content of the current conversation with the model. For single-turn queries, this contains one instance. For multi-turn queries (e.g., chat), this contains the conversation history and the latest request.
>`contents.role`	string	✅ Yes	-	`user` `model`	The role of the message sender.
>`contents.parts`	array	✅ Yes	-	-	The content parts of the message, which can contain different types of content (text, inlineData, etc.).
>>`contents.parts.text`	string	✅ Yes	-	-	The prompt for generating images. To include images or multiple images, refer to Multimodal Input.
`generationConfig`	object	❌ No	-	-	Configuration options for content generation.
>`generationConfig.imageConfig`	object	❌ No	-	-	Configuration for image generation. If set for models that don’t support these configuration options, the system will return an error. See Image Config for details.
>`generationConfig.responseModalities`	array	❌ No	-	`TEXT` `IMAGE`	The modalities of the response. If set for models that don’t support these configuration options, the system will return an error.
>`generationConfig.temperature`	number	❌ No	-	0.0-1.0	Controls the randomness of the output.

Multimodal Input

{
  "contents": [
    {
      "role": "user",
      "parts": [
        {
          "inlineData": {
            "mimeType": "image/jpeg",
            "data": "base64-encoded-image-data"
          }
        },
        {
          "text": "a cat"
        }
      ]
    }
  ]
}

parameter	Type	Required	Default	Range / Example	Description
`contents.parts`	array	✅ Yes	—	`text` `inlineData` `fileData`	The content parts of the message, which can contain different types of content .
>`contents.parts.inlineData`	object	❌ No	-	-	Inline media content. If used, `data` must be base64-encoded.
>>`contents.parts.inlineData.mimeType`	string	✅ Yes (if inline_data is used)	-	`image/png` `image/jpeg`	The IANA-standard MIME type of the source data. If the provided MIME type is not supported, the system will return an error.
>>`contents.parts.inlineData.data`	string	✅ Yes (if inline_data is used)	-	-	Base64-encoded media data.
>`contents.parts.fileData`	object	❌ No	-	-	File media content. If used, `fileUri` must be provided.
>>`contents.parts.fileData.mimeType`	string	✅ Yes (if file_data is used)	-	`image/png` `image/jpeg`	The IANA-standard MIME type of the source data. If the provided MIME type is not supported, the system will return an error.
>>`contents.parts.fileData.fileUri`	string	✅ Yes (if file_data is used)	-	-	The URI of the file to be processed.

Image Config

{
  "generationConfig": {
    "imageConfig": {
      "aspectRatio": "1:1",
      "imageSize": "1K"
    }
  }
}

parameter	Type	Required	Default	Range / Example	Description
`imageConfig`	object	❌ No	-	-	Configuration for image generation.
>`imageConfig.aspectRatio`	string	❌ No	-	`1:1` `2:3` `3:2` `3:4` `4:3` `9:16` `16:9` `21:9` `1:4` `4:1` `1:8` `8:1`	Aspect ratio of the generated image. If not specified, the model will select the appropriate aspect ratio based on the specified content. `1:4`, `4:1`, `1:8`, `8:1` are only supported by Gemini 3.1 Flash Image Preview.
>`imageConfig.imageSize`	string	❌ No	-	`0.5K` `1K` `2K` `4K`	Approximate size of the generated image. If not specified, the model will use the default value of 1K. `0.5K` is only supported by Gemini 3.1 Flash Image Preview; `2K` and `4K` are only supported by Gemini 3.1 Flash Image Preview and Gemini 3 Pro Image Preview.

Model Comparison

Feature	Gemini 2.5 Flash Image	Gemini 3.1 Flash Image Preview	Gemini 3 Pro Image Preview
Use case	Speed & efficiency	Speed & high-volume	Professional asset production
Supported sizes	1K	0.5K, 1K, 2K, 4K	1K, 2K, 4K
Max reference images	3	14	14
Max object images	—	10	6
Max portrait images	—	4	5
Extra aspect ratios	—	1:4, 4:1, 1:8, 8:1	—
Google Image Search Grounding	—	✅	—

Note:

Gemini 3.1 Flash Image Preview: Optimized for speed and high-volume use cases. Supports 0.5K resolution and extra ultra-wide/tall aspect ratios (1:4, 4:1, 1:8, 8:1). Also supports Google Image Search Grounding.
Gemini 3 Pro Image Preview: Optimized for professional asset production with advanced reasoning for complex creation tasks.
Gemini 2.5 Flash Image: Supports a maximum of 3 reference images and 1K resolution only.

Aspect Ratio & Image Size

By default, the model keeps the output image the same size as the input image; otherwise it produces a 1:1 square. You can control the aspect ratio of the generated image with the aspect_ratio field under image_config in your request, as shown below: Gemini 2.5 Flash Image

Aspect ratio	Resolution	Tokens
1:1	1024x1024	1290
2:3	832x1248	1290
3:2	1248x832	1290
3:4	864x1184	1290
4:3	1184x864	1290
4:5	896x1152	1290
5:4	1152x896	1290
9:16	768x1344	1290
16:9	1344x768	1290
21:9	1536x672	1290

Gemini 3.1 Flash Image Preview

Aspect ratio	512px resolution	0.5K tokens	1K resolution	1K tokens	2K resolution	2K tokens	4K resolution	4K tokens
1:1	512x512	747	1024x1024	1120	2048x2048	1120	4096x4096	2000
1:4	256x1024	747	512x2048	1120	1024x4096	1120	2048x8192	2000
1:8	192x1536	747	384x3072	1120	768x6144	1120	1536x12288	2000
2:3	424x632	747	848x1264	1120	1696x2528	1120	3392x5056	2000
3:2	632x424	747	1264x848	1120	2528x1696	1120	5056x3392	2000
3:4	448x600	747	896x1200	1120	1792x2400	1120	3584x4800	2000
4:1	1024x256	747	2048x512	1120	4096x1024	1120	8192x2048	2000
4:3	600x448	747	1200x896	1120	2400x1792	1120	4800x3584	2000
4:5	464x576	747	928x1152	1120	1856x2304	1120	3712x4608	2000
5:4	576x464	747	1152x928	1120	2304x1856	1120	4608x3712	2000
8:1	1536x192	747	3072x384	1120	6144x768	1120	12288x1536	2000
9:16	384x688	747	768x1376	1120	1536x2752	1120	3072x5504	2000
16:9	688x384	747	1376x768	1120	2752x1536	1120	5504x3072	2000
21:9	792x336	747	1584x672	1120	3168x1344	1120	6336x2688	2000

Gemini 3 Pro Image Preview

Aspect ratio	1K resolution	1K tokens	2K resolution	2K tokens	4K resolution	4K tokens
1:1	1024x1024	1120	2048x2048	1120	4096x4096	2000
2:3	848x1264	1120	1696x2528	1120	3392x5056	2000
3:2	1264x848	1120	2528x1696	1120	5056x3392	2000
3:4	896x1200	1120	1792x2400	1120	3584x4800	2000
4:3	1200x896	1120	2400x1792	1120	4800x3584	2000
4:5	928x1152	1120	1856x2304	1120	3712x4608	2000
5:4	1152x928	1120	2304x1856	1120	4608x3712	2000
9:16	768x1376	1120	1536x2752	1120	3072x5504	2000
16:9	1376x768	1120	2752x1536	1120	5504x3072	2000
21:9	1584x672	1120	3168x1344	1120	6336x2688	2000

Error Codes

Common Error Codes

Error Code	Error Name	Description
401	Unauthorized	API key is missing or invalid
403	Forbidden	Your API key doesn’t have permission to access this resource, or insufficient balance for the requested operation
429	Too Many Requests	You’ve exceeded your rate limit
500	Internal server error	An internal server error occurred
503	Content policy violation	Content blocked due to safety concerns (actual status code is 400)

API Reference

​Authentication

​Initiate Request

​Parameters

​Core Parameters

​Multimodal Input

​Image Config

​Model Comparison

​Aspect Ratio & Image Size

​Error Codes

​Common Error Codes