more bitmap view controls

[milliewalky]

• Exposure: scales the brightness of the image before tonemapping (if any) by 2^(exposure value); could be controlled via a slider.
• Offset: added to the image after exposure has been applied; also, a slider
• Gamma: exponent used when applying gamma tonemapping; perhaps gamma correction is more of a correct term here, but is not wrong if a visualisation engine treats gamma as one of several tonemap operators; also, a slider
• Tonemap operators: options include sRGB, gamma, FC (false-colour visualisation), and ± (positive/negative values; green for positive, red for negative); a toggle
• HDR mode (or perhaps LDR mode?): visualised values are not clamped to [0, 1]; note that this requires a display that supports HDR; a toggle

Cheers. If this feature set looks reasonable, and contributions are welcome, I’d be happy to help out.

[GloriousPtr]

Can we also have more formats like: BC1-BC7, R11G11B10_FLOAT etc