4 ms·

There's another way to hide the image, and that is to exploit the nonlinearity of the response curves (gamma). I have an image I crafted a long time ago which

There's another way to hide the image, and that is to exploit the nonlinearity of the response curves (gamma). I have an image I crafted a long time ago which looks something like gray noise when you open it up, but when you downscale it, you see an image of Lt Cmdr Data from Star Trek. I wonder if I can dig it up. The technique itself was not novel when I did it, a more sophisticated version involving embedded gamma values (which you can make quite large or small) was routinely used on image boards some ten or fifteen years ago.

VMG 6y ago
is it like this? http://www.ericbrasseur.org/gamma.html?i=1 http://www.ericbrasseur.org/gamma.html?i=1
- TeMPOraL 6y ago
  The article links to this browser test page: http://www.ericbrasseur.org/gamma_dalai_lama.html http://www.ericbrasseur.org/gamma_dalai_lama.html On my machine, both Firefox and Chrome display grey rectangles when scaling down. Why do the browsers get this wrong?
  - tech2 6y ago
    Because resizing in a linear colorspace is more costly. JPEG can be resized without shifting colorspaces VERY cheaply, but requires loading into RAM if a change in colorspace (or gamma shift) is performed. The hit can be quite significant. On a phone or laptop it would hurt battery, on an online service (dynamic resizer service) it would impact latency.
    - bawolff 6y ago
      > on an online service (dynamic resizer service) it would impact latency. If its even possible at all. Sometimes users upload things like https://commons.wikimedia.org/wiki/File:“Declaration_of_victory_after_the_Battle_of_Leipzig_on_18_October_1813”.jpg https://commons.wikimedia.org/wiki/File:“Declaration_of_vict...
  - deleted 6y ago
    [deleted]
  - choppaface 6y ago
    Can also depend on the monitor? When I drag this page between monitors I see different effects.
kuschku 6y ago
It's ridiculous that so few websites actually handle this well. Even my own self-written imgur clone does it just fine: https://i.k8r.eu/i/F_XCMA https://i.k8r.eu/i/F_XCMA https://i.k8r.eu/F_XCMAm.png https://i.k8r.eu/F_XCMAm.png https://i.k8r.eu/F_XCMAt.png https://i.k8r.eu/F_XCMAt.png You just have to go into a linear colorspace and use an area filter.
- 05greg 6y ago
  Related, You can get an idea of what your browser display is doing in this shadertoy: https://www.shadertoy.com/view/Wd2yRt https://www.shadertoy.com/view/Wd2yRt
- bawolff 6y ago
  Fwiw, the reason why wikipedis doesn't do this when rescaling images (or at least didn't years ago when i was working on image resizing code for wikipedia) is that to do that (with off the shelf software) required keeping the entire image in memory, which was a big no no. I mean, i guess it would be fine for small images, but then you're using two different algorithms depending on image size, which seems bad.

VMG 6y ago

is it like this? http://www.ericbrasseur.org/gamma.html?i=1 http://www.ericbrasseur.org/gamma.html?i=1

TeMPOraL 6y ago
The article links to this browser test page: http://www.ericbrasseur.org/gamma_dalai_lama.html http://www.ericbrasseur.org/gamma_dalai_lama.html On my machine, both Firefox and Chrome display grey rectangles when scaling down. Why do the browsers get this wrong?
- tech2 6y ago
  Because resizing in a linear colorspace is more costly. JPEG can be resized without shifting colorspaces VERY cheaply, but requires loading into RAM if a change in colorspace (or gamma shift) is performed. The hit can be quite significant. On a phone or laptop it would hurt battery, on an online service (dynamic resizer service) it would impact latency.
  - bawolff 6y ago
    > on an online service (dynamic resizer service) it would impact latency. If its even possible at all. Sometimes users upload things like https://commons.wikimedia.org/wiki/File:“Declaration_of_victory_after_the_Battle_of_Leipzig_on_18_October_1813”.jpg https://commons.wikimedia.org/wiki/File:“Declaration_of_vict...
- deleted 6y ago
  [deleted]
- choppaface 6y ago
  Can also depend on the monitor? When I drag this page between monitors I see different effects.

kuschku 6y ago

It's ridiculous that so few websites actually handle this well. Even my own self-written imgur clone does it just fine: https://i.k8r.eu/i/F_XCMA https://i.k8r.eu/i/F_XCMA https://i.k8r.eu/F_XCMAm.png https://i.k8r.eu/F_XCMAm.png https://i.k8r.eu/F_XCMAt.png https://i.k8r.eu/F_XCMAt.png You just have to go into a linear colorspace and use an area filter.

05greg 6y ago
Related, You can get an idea of what your browser display is doing in this shadertoy: https://www.shadertoy.com/view/Wd2yRt https://www.shadertoy.com/view/Wd2yRt
bawolff 6y ago
Fwiw, the reason why wikipedis doesn't do this when rescaling images (or at least didn't years ago when i was working on image resizing code for wikipedia) is that to do that (with off the shelf software) required keeping the entire image in memory, which was a big no no. I mean, i guess it would be fine for small images, but then you're using two different algorithms depending on image size, which seems bad.