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HDR is “High Dynamic Range”.
Most DSLR’s have a dynamic range of 5, maybe 6 stops; that is, they can record tones ranging from Black through to White over an F-stop range of say, F2.8 to F16.
So, if you were at a wedding where the bride was wearing a beautiful white dress with lots of lacy detail and delicate frills, but the groom was dressed in a black suit with a fine, dark grey pin stripe, a single exposure may not reveal both the texture of the black suit, its fine pin strip and the subtle tones in the lacy detail.
If you expose for the lacy detail, the grooms suit will look jet black, blocky with no detail.
If you expose for the black suit to show the fine pin stripe and the texture of the material, the brides’ dress will be blown out, a pure, dazzling white blob with no detail in the lace and frilly bits.
HDR is where you would take say, at least 3 shots. One correctly exposed for the black suit; one correctly exposed for the brides white dress and then one correctly exposed for the 18% grey mid tones.
The HDR process would then combine all three photos to reveal the detail available in the blacks, mid-tones and whites, provided no-one moved between the 3 exposures.
Cheers
Dennis
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