Comment améliorer les images Flux AI jusqu'à une résolution prête pour l'impression

I switched to Flux about two months ago, mostly out of frustration with Midjourney's content filters rejecting half my prompts for no reason I could understand. The first thing I noticed was how photographic the outputs looked. Better lighting than Midjourney. Better depth of field. Colors that felt natural instead of stylized.

The second thing I noticed was that there is no upscale button. Midjourney at least gives you the U1 through U4 buttons and a few upscaling modes. They are not great, which I wrote about earlier, but they exist. Flux gives you nothing. Your image comes out at the generation resolution and that is it.

For the first few weeks I just accepted it. I was making images for social media and 1024x1024 was fine. Then I wanted to print a few of my favorite Flux generations. That was when I realized 1024 pixels at 300 DPI is 3.4 inches. Smaller than a postcard. I needed to figure out external upscaling fast.

What resolution you actually get from Flux

Flux.1 Pro, Dev, and Schnell all output at roughly the same base resolution. Usually 1024x1024 for square images, with some aspect ratio variations like 1024x768 or 768x1024. Some hosted versions of Flux Pro offer slightly higher maximums, but I have never seen one go past about 1440 pixels on the long edge.

Here is what those resolutions mean for actual use. At 1024x1024, you can print at 3.4 inches at 300 DPI. That is a coaster, not a print. Even at 1440 pixels, you are at 4.8 inches. Fine for a greeting card, not for framing. For a proper 8x10 print you need 2400x3000 pixels. For an 11x14 you need 3300x4200.

The math is simple. If you want to print Flux images at any standard frame size, you need to upscale them. There is no way around it.

Flux images upscale better than Midjourney images

Here is something interesting I noticed after upscaling about 60 Flux generations and comparing them to upscaled Midjourney outputs. Flux images tend to handle the upscaling process better. They come out cleaner.

I think the reason is that Flux generates more natural looking images to begin with. The lighting is more realistic, the textures are less stylized, the color grading is subtler. All of these characteristics align well with what external upscalers like Real-ESRGAN were trained on. The model was trained on real photographs, and Flux images look more like real photographs than Midjourney images do.

Midjourney images sometimes have a slightly painterly quality that the upscaler does not quite know how to handle. It tries to add realistic texture to what was supposed to be a stylized surface. Flux images do not have this problem as often. The base image already looks photographic, so the upscaler just enhances what is there instead of trying to reinterpret it.

My actual workflow for Flux images

I keep this extremely simple because I have found that fewer steps almost always produces better results with AI tools. Every additional processing pass is another chance for something to go wrong.

First, export as PNG. This is even more important with Flux than with Midjourney because some Flux interfaces default to JPEG. Check your settings. If your Flux provider only gives you JPEG, find a different provider. The compression artifacts in JPEG will be amplified when you upscale and you will not get clean results at 4K.

Second, upscale 4x using Real-ESRGAN. This takes about five to eight seconds and costs 4 credits. Your 1024x1024 image becomes 4096x4096. That prints at 13.6 inches at 300 DPI. Good enough for most standard frame sizes. If you only need it for web or screen display, a 2x upscale to 2048x2048 costs 2 credits and is sufficient.

Third, check for faces. Flux handles faces better than most generators at the base resolution, but after upscaling you might notice some softness around facial features. If there are people in the image, run a face restoration pass. That adds 4 credits. If the image has no faces or the faces look sharp enough, skip it.

That is three steps. Two if your image has no people. Four to eight credits total. Under 15 seconds of processing time. This is the simplest part of my entire Flux workflow.

Schnell vs. Pro for upscaling

I use Schnell a lot because it is fast and cheap. But I learned the hard way that Schnell images do not upscale as well as Pro images. Schnell trades some base quality for speed, and that quality gap gets wider when you upscale.

At the base 1024x1024 resolution, the difference between a Schnell output and a Pro output is noticeable but not dramatic. At 4096x4096 after a 4x upscale, it becomes obvious. Schnell images show more artifacts. Fine details are slightly less crisp. Smooth gradients sometimes develop subtle banding.

My rule now is that for anything I plan to print or sell, I use Flux Pro for the generation and then upscale 4x. For social media posts and quick experiments, Schnell at 2x upscale is fine. Match the quality of your source to how much the final output matters.

What about Flux Pro's higher resolution options?

Some hosted Flux Pro instances let you generate at slightly higher resolutions. I have seen up to about 1440 pixels on the long edge. This helps but it does not solve the fundamental problem. Even at 1440 pixels, you are still under 5 inches at 300 DPI. You still need to upscale for printing.

The higher base resolution does give the upscaler more data to work with, which produces marginally better results at 4x. But the difference is small. A 1024 source upscaled to 4096 looks maybe 90% as good as a 1440 source upscaled to 5760. For most people, the extra generation cost for higher base resolution is not worth the marginal improvement.

Flux is the best image generator I have used. But it is half a tool without external upscaling. If you are using Flux and have never upscaled your outputs, try running your favorite generation through a 4x upscale and look at them side by side at 100% zoom. You cannot unsee the difference.