24 bits per pixel for a color image) are considered Low Dynamic Range.ġ6-bit images (i.e. However, the number of bits itself may be a misleading indication of the real dynamic range that the image reproduces - converting a Low Dynamic Range image to a higher bit depth does not change its dynamic range, of course. Most often, the distinction is made depending on the number of bits per color channel that the digitized image can hold. Whether an image may be considered High or Low Dynamic Range depends on several factors. In this sense, HDR images are scene-referred, representing the original light values captured for the scene. This means that the value of a pixel from an HDR image is proportional to the amount of light measured by the camera.
floating-point values stored with 32 bits per color channel.Īnother characteristics of an HDR image is that it stores linear values. Therefore, an HDR image is encoded in a format that allows the largest range of values, e.g. An HDR (High Dynamic Range) image stores pixel values that span the whole tonal range of real-world scenes. The Dynamic Range of real-world scenes can be quite high - ratios of 100,000:1 are common in the natural world. The scanline below represents the log base 10 of the luminance, so going from 0.1 to 1 is the same distance as going from 100 to 1000, for instance.Ī scene showing the interior of a room with a sunlit view outside the window, for instance, will have a dynamic range of approximately 100,000:1. To make it easier to represent values that vary so widely, it is common to use a logarithmic scale to plot the luminance. The human eye can accommodate a dynamic range of approximately 10,000:1 in a single view.
The luminance of the sun itself is approximately 1,000,000,000 cd/m2. While the luminance of starlight is around 0.001 cd/m2, that of a sunlit scene is around 100,000 cd/m2, which is a hundred millions times higher. The range of luminance human vision can handle is quite large. In photography and imaging, the dynamic range represents the ratio of two luminance values, with the luminance expressed in candelas per square meter. Dynamic range is a ratio and as such a dimensionless quantity.
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