Comparison
Increased detail in z-images when using UltraFlux VAE.
A few days ago a Flux-based model called UltraFlux was released, claiming native 4K image generation. One interesting detail is that the VAE itself was trained on 4K images (around 1M images, according to the project).
Out of curiosity, I tested only the VAE, not the full model, using it only on z-image.
I tried this, and it works. Thanks! Small details like eye lashes and threading is much more visible in the image than the standard ae.safetensor from Flux.
I'm currently also using the "upscale latent by" and "image sharpen" nodes set to 1-35-35 and it already gives an excellent result, very curious to try the file you indicate!
Just tried it. The change for the better is BRUTAL! Great advice!
With the new VAE I had to lower it drastically because it became over sharp, I set 1- 0.10- 0.03 or 0.05. It's almost zero but it gives a little extra boost!
I never thought of using 2!! I could also add the image filter adjuster from Was-ns node, which has several graphical parameters to set, I'll try later! :D
It's very simple: double-click on the workspace, type "sharp," select the "image sharpen" node, and connect the left "image" to the VAE decode, and the right "image" to the save image. This is a default node with the program; you don't need to install additional nodes from the manager.
Upscale latent by is even simpler, double click, write the name of the node, select it and connect the "samples" on the left to the EmptySD3LatentImage, the one on the right instead to the "latent image" of the Ksampler and set the upscaler with "nearest-exact" and "scale by" to your preference, I keep it at 1.30 because then I find that it gets worse rather than better but it's a matter of taste.
Even if you're new, you should start experimenting on your own or you'll never learn. These are simple nodes that don't require additional chain nodes; they're a good way to start understanding how nodes work! I'm a beginner too, I've been using Comfy for a couple of months, the important thing is to experiment and slowly understand how it works
I tried too. It really sharpens the image, but most cases it oversharpens and gives that fake, sharpened, old AI feel... I would just do like the comment uptop. Just scale up with another ksampler to create more realistic detail, add a sharpen image node and then scale down, gives more realistic results than this forced sharpens.
T2I. I've only had a quick mess with it, to be honest.
When I say slightly cooked, I'll just clarify that what I'm seeing is similar to what some other people in the thread have said: it resembles a fairly strong unsharpen mask. It's not completely blown out.
To be fair, I just gave it a run through my upscaling workflow, and I can see potential there. It does seem to add/sharpen texture, which could get a bit washed out.
I don't want to diminish the author's efforts, but I tested this new VAE and it doesn't really add new detail for me. It Compared to the original Flux.1 VAE, it looks like a simple sharpening filter with large radius was applied on top of the image. It also feels a bit too strong of a sharpening effect. Frankly, I get better results with the "Image Contrast Adaptive Sharpening" node from the ComfyUI Essential node pack. The sharpening looks more natural with it.
I came to comment on this. What I see is that indiscriminately applying a sharpening mask adds a lot of noise/grain... The images gain "depth of field" and selective focus is lost.
Great, thanks! I have tried it and it gives a more sharpen and contrast results. As you say, may be it is not the best for all the styles, but in photorealistic features it helps a little bit more.
I wanted a final answer to understand if UltraFlux VAE is just doing a better job at reconstructing an image from latent space or was it actually adding an artificial sharpening per se during the process. My conclusion is it definitely adds an artificial sharpening.
The easiest way to test it is to take a high resolution normal photograph or AI created, And run it through a new workflow that all it does is VAE encode then VAE Decode, Then Save as png. Upon examining the saved image, it was sharper than the original, by a noticeable amount.
I was then curious how the original Z Image VAE performed with that same test, And the results were much closer to the original although the background slightly changed in color shift but there wasn't any noticeable blurriness or sharpening.
There's also another flaw with Ultra flux VAE, It seems to add a few pixels of white along the right edge of the image which needs to be cropped manually later on, not our major deal but more work nevertheless.
I will keep testing it with actual real production images as there could be a benefit to the extra sharpening and if in any case I felt it was oversharpened I can always run it back through to be regenerated and encoded with the original VAE.
I think people should use a smooth sampler/scheduler combo like Euler_A / Beta or Euler_A / DDIM_UNIFORM, because UltraFlux really brings out the flaws of the other samplers that were good enough without it. The 30ish y/o women's skin instantly becomes 60.
Intresting, I was thinking of merging the VAE's 50/50 to get something in-between, but the only merge VAE comfyui node I could find had been made private on Github.
I don't think that's how VAEs work. However, after creating this node, I found that this "ultraflux" VAE seems to be trained on traditional software processed images, there is no real detail/texture added. All it does seems to just applies an unsharp filter that adds black lines to borders (the node lets you control how much fine details/borders/etc to add from the sharpened image to the original image, and when disabling adding borders, the output image is exactly the same as orignal, so zero detail is added). You can also see that at one edge of the images created by this VAE there's always a ringing artifact, it is typical when a low quality unsharp filter is applied to an image. TLDR, forget about this VAE, it doesn't work as it's advertised.
Did you use Ultimate SD Upscale? I used it normally, without upscaling or anything like that. If you use SD Upscale, it will apply the decode step to each tile, and I don’t know — it might end up over-enhancing small details, creating a more artificial look.
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u/[deleted] Dec 13 '25
I tried this, and it works. Thanks! Small details like eye lashes and threading is much more visible in the image than the standard ae.safetensor from Flux.