You don't need Midjourney. You don't need a $20/month subscription. You don't need to upload your prompts to anyone's server. Your iPhone can run Stable Diffusion entirely on device using the Neural Engine that Apple designed specifically for this kind of workload.
Off Grid is a free, open-source app that runs AI image generation on your iPhone's hardware through Apple's Core ML pipeline. 8 to 15 seconds per image on iPhone 15 Pro. Your prompts and your images never leave your phone.
What You Need
Minimum: iPhone 12 (A14 Bionic), iOS 17+. Palettized models (about 1GB) will run. Expect 20 to 35 seconds per image.
Recommended: iPhone 15 Pro or newer (A17 Pro). 8GB of RAM and a more powerful Neural Engine make a real difference. 8 to 15 seconds per image.
Storage: Palettized models are about 1GB. Full precision models are about 4GB. Start with palettized.
How It Works on iPhone
Off Grid uses Apple's ml-stable-diffusion pipeline to run image generation through Core ML, targeting the Neural Engine directly. The Neural Engine is a dedicated AI accelerator built into every Apple chip since the A11. It's separate from the CPU and GPU and specifically optimized for the kind of math that diffusion models depend on.
The model starts with random noise and refines it over multiple denoising steps into the image your prompt described. Off Grid shows a real-time preview during generation so you can watch it form. All computation happens on your phone's silicon. No server involved after the initial model download.
Image Generation
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Palettized vs Full Precision: Which to Download
This is an iOS-specific choice that matters.
Palettized models (6-bit, about 1GB): Designed by Apple specifically for memory-constrained devices. They use a compression technique called palettization that dramatically reduces file size. Quality is surprisingly good for the footprint. Best choice for iPhones with 6GB RAM or less.
Full precision models (fp16, about 4GB): Higher quality with finer detail. Faster on the Neural Engine because there's no depalettization overhead. But they need significantly more RAM. Best for iPhone 15 Pro and newer with 8GB.
Start with palettized. If the quality meets your needs (it probably will), save the storage.
Real World Performance
iPhone 16 Pro / 15 Pro (A17 Pro / A18 Pro, 8GB): 8 to 12 seconds at 512x512, 20 steps with full precision. 6 to 10 seconds with palettized.
iPhone 14 / 15 (A15 / A16, 6GB): 15 to 25 seconds with palettized models. Full precision may cause memory pressure. Stick with palettized.
iPhone 12 / 13 (A14 / A15, 4GB): 20 to 35 seconds with the smallest palettized models. Usable but not fast. Close all other apps first.
20+ Models to Choose From
Off Grid includes a model browser with over 20 Stable Diffusion models sorted by style and device compatibility:
Absolute Reality for photorealistic output. Faces, landscapes, product shots.
DreamShaper for a balanced artistic style. Good default choice.
Anything V5 for anime and illustration. Clean lines, vivid colors.
The browser shows which models work with your specific iPhone so you never download something that won't run.
The Feature That Changes Everything: AI Prompt Enhancement
This is what makes Off Grid different from a basic Stable Diffusion wrapper.
Type "a castle." Raw Stable Diffusion gives you a generic result. But Off Grid also runs LLMs on device, and it chains text generation with image generation.
Enable prompt enhancement and your simple prompt first goes through the loaded text model. It expands "a castle" into a detailed description with artistic style, lighting, mood, composition, and quality modifiers. That enhanced prompt then goes to Stable Diffusion, and the output quality difference is dramatic.
You see the enhanced prompt before generation starts. Cloud image generators do this behind the scenes. Off Grid does it transparently, on your phone, and you control every step.
Tips for Better Results
Always use prompt enhancement. The quality jump is immediately visible. A three-word prompt enhanced by the text model consistently produces better results than a manually crafted long prompt.
20 denoising steps is the sweet spot. Higher step counts improve quality marginally while increasing time linearly. 20 gives you clean, detailed images.
512x512 resolution. The standard for on-device Stable Diffusion. Higher resolutions multiply memory and time requirements. At phone screen distances, 512x512 looks sharp.
Negative prompts help. Adding "blurry, low quality, distorted, deformed" pushes the model away from common artifacts. Especially useful with palettized models.
Give your phone a break between batches. Sustained generation heats up the phone and triggers thermal throttling. A 30-second pause between images keeps performance consistent.
Privacy for Creative Work
Every image you generate on cloud services is stored on their servers. Your prompts are logged. Depending on the service, your generated images and the prompts that created them may be used to train future models.
With Off Grid, your prompts and images exist only on your phone. There's no server, no logging, no possibility of your creative process being used to improve someone else's product. The App Store privacy label says it directly: the developer does not collect any data from this app.
Open source. MIT licensed. Verify it yourself.
Getting Started
- Install Off Grid from the App Store
- Download a Stable Diffusion model from the in-app browser (start with palettized, about 1GB)
- Switch to image generation mode
- Type a prompt or let the AI enhance it for you
- Watch the real-time preview as your image forms
Off Grid also runs text generation, voice transcription, vision, tool calling, and document analysis. All offline, all in the same app. Check the GitHub for the latest updates.
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