9 ms·

Although the article is dated 2007, the error it describes is still present in every implementation I've tested. There's a test page for browsers at: http://ww

Although the article is dated 2007, the error it describes is still present in every implementation I've tested. There's a test page for browsers at: http://www.4p8.com/eric.brasseur/gamma_dalai_lama.html http://www.4p8.com/eric.brasseur/gamma_dalai_lama.html

_delirium 17y ago
Are projects like Gimp and ImageMagick not yet aware of it, don't consider it a bug, just haven't gotten around to fixing it, or what? In some brief trawling through bugtrackers and mailing lists I haven't been able to find any discussion on the subject, but it's somewhat hard to search on variations of the widely used terms "gamma", "scaling", and "bug".
- petewarden 17y ago
  Part of the issue is that people have been trained by two decades of Photoshop and expect the results of the 8-bit algorithms. Gaussian blur for example looks very different in linear light, with light areas of the image blooming out over the darker. If you've spent years working with the 8 bit gamma space algorithms, that's a bug. Instead, I've ended up implementing both algorithms, usually with the more correct one labeled as 'defocus' or 'camera blur'. Rescaling and in general resampling is a lot simpler. These days it's pretty inexcusable not to do it in linear space. Here's my own exploration of that problem from a couple of years back: http://petewarden.typepad.com/searchbrowser/2008/08/why-fonts-need.html http://petewarden.typepad.com/searchbrowser/2008/08/why-font...
  - jacobolus 17y ago
    Because human visual response is non-linear, doing operations like gaussian blur (which is an artificial operation, unrelated to physical phenomena) in linear light space isn’t “more correct” in any absolute sense. Calling a gaussian blur “camera blur” or “defocus” (whatever the color space) is just inaccurate and confusing. Compositing and interpolating should definitely be done in linear space though.
    - petewarden 17y ago
      > Calling a gaussian blur “camera blur” or “defocus” (whatever the color space) is just inaccurate and confusing. Nonsense. When you defocus a camera, you get an effect that's comparable with a gaussian blur performed in linear space. Blurring is a well-understood operation that's existed for a long time in the analog world, before we ever did any digital processing.
      - jacobolus 17y ago
        Well, “comparable” insofar as you don’t care about the details, I suppose; you could also call a square or triangle blur kernel “defocus” if you wanted. A real lens blur doesn’t look much like a gaussian blur for someone who is familiar with both and paying attention. For explanation, see for instance http://en.wikipedia.org/wiki/Bokeh http://en.wikipedia.org/wiki/Bokeh
        petewarden 17y ago
        Yep, my 'camera defocus' also included arbitrary kernel geometry as an option! I'm not trying to be obnoxious about this, but I really did spend five years of my life coding this stuff for Apple.
    - scythe 17y ago
      >human visual response is non-linear Human visual response to color is also nonlocal, which has an array of interesting effects.
- jacobolus 17y ago
  You can make ImageMagick do quite sophisticated image interpolation, if you want. Pretty sure GIMP’s main goal is to just do what Photoshop does.

_delirium 17y ago

Are projects like Gimp and ImageMagick not yet aware of it, don't consider it a bug, just haven't gotten around to fixing it, or what? In some brief trawling through bugtrackers and mailing lists I haven't been able to find any discussion on the subject, but it's somewhat hard to search on variations of the widely used terms "gamma", "scaling", and "bug".

petewarden 17y ago
Part of the issue is that people have been trained by two decades of Photoshop and expect the results of the 8-bit algorithms. Gaussian blur for example looks very different in linear light, with light areas of the image blooming out over the darker. If you've spent years working with the 8 bit gamma space algorithms, that's a bug. Instead, I've ended up implementing both algorithms, usually with the more correct one labeled as 'defocus' or 'camera blur'. Rescaling and in general resampling is a lot simpler. These days it's pretty inexcusable not to do it in linear space. Here's my own exploration of that problem from a couple of years back: http://petewarden.typepad.com/searchbrowser/2008/08/why-fonts-need.html http://petewarden.typepad.com/searchbrowser/2008/08/why-font...
- jacobolus 17y ago
  Because human visual response is non-linear, doing operations like gaussian blur (which is an artificial operation, unrelated to physical phenomena) in linear light space isn’t “more correct” in any absolute sense. Calling a gaussian blur “camera blur” or “defocus” (whatever the color space) is just inaccurate and confusing. Compositing and interpolating should definitely be done in linear space though.
  - petewarden 17y ago
    > Calling a gaussian blur “camera blur” or “defocus” (whatever the color space) is just inaccurate and confusing. Nonsense. When you defocus a camera, you get an effect that's comparable with a gaussian blur performed in linear space. Blurring is a well-understood operation that's existed for a long time in the analog world, before we ever did any digital processing.
    - jacobolus 17y ago
      Well, “comparable” insofar as you don’t care about the details, I suppose; you could also call a square or triangle blur kernel “defocus” if you wanted. A real lens blur doesn’t look much like a gaussian blur for someone who is familiar with both and paying attention. For explanation, see for instance http://en.wikipedia.org/wiki/Bokeh http://en.wikipedia.org/wiki/Bokeh
      - petewarden 17y ago
        Yep, my 'camera defocus' also included arbitrary kernel geometry as an option! I'm not trying to be obnoxious about this, but I really did spend five years of my life coding this stuff for Apple.
  - scythe 17y ago
    >human visual response is non-linear Human visual response to color is also nonlocal, which has an array of interesting effects.
jacobolus 17y ago
You can make ImageMagick do quite sophisticated image interpolation, if you want. Pretty sure GIMP’s main goal is to just do what Photoshop does.