A social platform gag
The thumbnail is a landscape, and opening it full-screen on a dark interface reveals a different picture.
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Guide
Mirage Tank combines two images into one special PNG: in a thumbnail on a white background you see the surface image, and opened full-screen on a black background you see the hidden image. The principle is that a pixel has only two quantities, grey and opacity, and the displayed colour is grey × opacity + background × (1 − opacity); by compressing the surface image into the bright 0.5–1 range and the hidden image into the dark 0–0.5 range, a grey and an alpha can be solved for every pixel, reproducing the surface on white and the hidden image on black. The processing happens locally in the browser.
Updated 2026-09-093 min read
Mirage Tank combines two images into one special PNG: in a thumbnail on a white background you see the surface image, and opened full-screen on a black background you see the hidden image. The principle is that a pixel has only two quantities, grey and opacity, and the displayed colour is grey × opacity + background × (1 − opacity); by compressing the surface image into the bright 0.5–1 range and the hidden image into the dark 0–0.5 range, a grey and an alpha can be solved for every pixel, reproducing the surface on white and the hidden image on black. The processing happens locally in the browser.
It is the visual version of image steganography: steganography hides text invisibly, while a mirage tank hides another picture that appears when the background colour changes.
| Input | Output | Notes |
|---|---|---|
Surface: a photo of a white cat; hidden: a night scene; width 1200 |
A greyscale translucent PNG 1200 px wide by the surface ratio |
White background shows the cat, black shows the night scene |
Surface 16:9, hidden 1:1 |
The hidden image is centre-cropped to 16:9 before combining |
Cover cropping, never stretched |
A very dark surface and a very bright hidden image |
Both sides look grey and low in contrast |
The surface has to be bright and the hidden image dark for a clear effect |
The thumbnail is a landscape, and opening it full-screen on a dark interface reveals a different picture.
A web page shows a different greyscale illustration in light and dark mode.
Hide an answer in the hidden image so it only appears on a black background.
Use the white and black previews to show alpha compositing in a lesson.
The platform compressed the PNG into JPG and the alpha channel is gone. Send it as the “original” or as a file, or use a platform that keeps PNG transparency.
No, this version only outputs greyscale; a colour mirage tank needs a different algorithm.
The surface should be bright overall and the hidden image dark overall, and the two compositions should differ a lot; switch between the white and black previews a few times before downloading.
The two images are combined pixel by pixel locally in the browser and are never uploaded to any server; they are released from memory when the page is closed.
Updated 2026-09-09
Blend two images into one PNG that shows one picture on white and another on black
A phantom tank exploits how semi-transparent grey pixels look against different backgrounds: displayed colour = pixel grey × opacity + background colour × (1 − opacity). The surface image is compressed into the bright range and the inner image into the dark range, and each pixel gets a grey value and an opacity that restore the surface image on white and the inner image on black.
Note: send the original PNG or the effect is lost (the alpha channel must survive); if a platform re-compresses the image as JPG it stops working. The output is greyscale, so colour information is not kept.