Color spaces, gamma and image enhancement

Question

Color space. Well, everybody knows about RGB: three values normalized in the range [0.0,1.0], which have the meaning of the intensity of the color components Red Green Blue; this intensity is meant as linear, isn't?

Gamma. As far I can understand, gamma is a function which maps RGB color components to another value. Googling on this, I've seen linear functions and non linear functions... Linear functions seems to scale RGB components, so it seems to tune image brightness; non linear functions seems to "decompress" darker/lighter components.

Now, I'm starting to implement an image viewer, which shall display different image formats as texture. I'd like to modify the gamma of these images, so I should build up a fragment shader and run over the textured quad. Fine, but how do I determine the right gamma correction?

OpenGL works using linear RGB color space, using floating point components. Indeed, I could compute gamma-corrected values starting from those values (with special floating point precision), so they are displayed after having clamped the gamma-corrected value.

First, I shall determine the gamma ramp. How could I determine it? (analitically or using lookup tables)

Then, I came up to investigate on the OpenGL extension EXT_framebuffer_sRGB, which seems very related with the extension EXT_texture_sRGB.

EXT_texture_sRGB introduce a new texture format which is used to linearize textel values into RGB linear space. (footnote 1) In this way, I'm aware of sRGB color space and use it as linear RGB color space.

Instead, EXT_framebuffer_sRGB extension allows me to encode linear RGB values onto the sRGB framebuffer, without worrying about it.

...

Wait, all this information for what? If I can use sRGB framebuffer and load sRGB textures, process that textures without sRGB conversions... why should I correct gamma?

Maybe can I correct gamma all the same, even on a sRGB buffer? Or I better not? And brightness and contrast: shall they applied before or after gamma correction?

That's a lot of information, I'm getting confused now. Hope that someone of you can explain me more all these concepts! Thank you.

...

There's another question. In the case the device gamma is different from the "standard" 2.2, how do I "accumulate" different gamma corrections? I don't know if it is clear: in the case image RGB values are already corrected for a monitor with a gamma value of 2.2, but the monitor has a gamma of value 2.8, how to I correct gamma?

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(1) Here is some extract to highlight what I mean:

The sRGB color space is based on typical (non-linear) monitor characteristics expected in a dimly lit office. It has been standardized by the International Electrotechnical Commission (IEC) as IEC 61966-2-1. The sRGB color space roughly corresponds to 2.2 gamma correction.

Does this extension provide any sort of sRGB framebuffer formats or guarantee images rendered with sRGB textures will "look good" when output to a device supporting an sRGB color space?

   RESOLVED:  No.

  Whether the displayed framebuffer is displayed to a monitor that
    faithfully reproduces the sRGB color space is beyond the scope
    of this extension.  This involves the gamma correction and color
    calibration of the physical display device.

    With this extension, artists can author content in an sRGB color
    space and provide that sRGB content for use as texture imagery
    that can be properly converted to linear RGB and filtered as part
    of texturing in a way that preserves the sRGB distribution of
    precision, but that does NOT mean sRGB pixels are output
    to the framebuffer.  Indeed, this extension provides texture
    formats that convert sRGB to linear RGB as part of filtering.

    With programmable shading, an application could perform a
    linear RGB to sRGB conversion just prior to emitting color
    values from the shader.  Even so, OpenGL blending (other than
    simple modulation) will perform linear math operations on values
    stored in a non-linear space which is technically incorrect for
    sRGB-encoded colors.

    One way to think about these sRGB texture formats is that they
    simply provide color components with a distribution of values
    distributed to favor precision towards 0 rather than evenly
    distributing the precision with conventional non-sRGB formats
    such as GL_RGB8.