
Photomatix Pro 5.0 User Manual 37
HDR Image
Strictly speaking, an HDR image is an intermediary image with 32 bits per color chan-
nel (96 bits per pixel)� An HDR image is the result of merging photos of the same
scene taken under dierent exposure settings and stored in special HDR image
format� The 32-bit intermediary HDR image must be processed with tone mapping
for proper display on standard monitors and prints� It has become very common to
dene "HDR image" as the result of processing the 32-bit HDR image with tone map-
ping, i�e� the tone mapped output, but this is not technically correct�
Histogram
Histograms represent brightness distribution in digital images� They help evaluate
correct exposure� The y-axis represents the amount of pixels and the x-axis represents
the brightness value�
JPEG
A common image le format with two primary strengths – a relatively small le size
and universal compatibility� JPEGs use a lossy compression scheme and should not
be edited and re-saved�
Noise
Statistical variations inherent in the sensor system cause noise� Noise is always pres-
ent, but higher sensitivities and smaller sensors usually generate more noise�
Pixel
Digital pictures consist of pixels, the smallest units� Each pixel has a color that can be
represented by 8 or 16 bits or as a oating-point number (32bit HDR)�
PPI
Pixels per Inch� Can be used to describe the actual pixels per inch of a print� Often
confused with DPI (Dots per Inch), used by color printers to print an image�
RAW File
A le containing the raw data from the camera sensor� RAW les do not have a color
prole or other stylistic preferences permanently applied�
TIFF
A comprehensive image format that oers lossless compression schemes for smaller
le sizes with higher quality� This format is suitable for editing and printing but not
publishing on the Web�
Tone Mapping
Processing a 32-bit HDR image into an image that can be properly viewed on
monitors and in prints�
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