MiniMax-H3-Image-VAE

Experimental MiniMax H3 single-image VAE

An experimental image-specialized MiniMax H3 VAE that directly decodes a single temporal latent (T=1) into one image. It was made to provide a usable direct-one-latent image path, not as a claim of state-of-the-art or high-fidelity image reconstruction. It is distributed as a standard merged H3 VAE checkpoint: no custom node or separate decoder head is required.

[!IMPORTANT] This checkpoint is for images only. Do not use it as a replacement for the original H3 VAE in video workflows. Its image-specialized decoder materially regresses multi-frame video reconstruction and can introduce patch-grid ghosting and cross-frame mixing. Keep the original MiniMax H3 VAE for video.

[!NOTE] Reconstruction quality is limited. Outputs can remain soft and can lose fine text, thin contours, hair, foliage and microtexture; the example below is intended to show the actual result rather than imply a quality guarantee.

Example

Source images are shown on the left and reconstructions from this VAE on the right.

How it was trained

The original H3 encoder was frozen while the full decoder and post_quant_conv were fine-tuned to reconstruct the real source image directly from one H3 temporal latent. Training used a progressive 256→384 px curriculum and one pass over 51,083 unique images (41,259 Booru Essence images and 9,824 pseudo-camera photographs), with a decoder-aware objective combining Charbonnier reconstruction, edge, SSIM, and low-weight FDL/FDL-PIPS losses. The selected step-1597 decoder was merged back into the standard H3 VAE checkpoint, so it loads through normal H3 VAE tooling.

Validation

On a balanced unseen 512 px set containing 32 photographs and 32 art images, the selected checkpoint measured:

• 30.4425 dB PSNR
• 0.939257 SSIM
• 0.016817 MAE

The two live ComfyUI examples above reached 31.8420 dB / 0.898509 SSIM and 32.0064 dB / 0.940569 SSIM. Additional deployment checks from approximately 1 to 3 megapixels reached 31.55–33.43 dB PSNR.

ComfyUI usage

Download minimax_h3_t1_image_vae_step1597.safetensors into:

ComfyUI/models/vae/

Load it with ComfyUI's standard Load VAE node and use the normal VAE encode/decode nodes. The model expects MiniMax H3's 24-channel latent format and is intended for single-image (T=1) round trips.

Checkpoint

• Size: 5,207,808,784 bytes
• SHA-256: 6c3d0bfa055986a803a566a862fcde283a1e63db62829e5ef4a2a5aebf50bb86
• Training checkpoint: step 1597

Model usage remains subject to the applicable MiniMax H3 license and terms.