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range
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... represents calibrated color information (if the cHRM chunk is
present) or uncalibrated device-dependent color (if cHRM is
absent). All color values range from zero (representing black) to
most intense at the maximum value for the sample depth. Note that
the maximum value at a given sample depth is (2^sampledepth)-1,
...
... The first entry in PLTE is referenced by pixel value 0, the
second by pixel value 1, etc. The number of palette entries
must not exceed the range that can be represented in the image
bit ...
... permissible to have fewer entries than the bit depth would
allow. In that case, any out-of-range pixel value found in the
image data is an error.
...
... PNG specifies that only certain sample
depths can be used, and further specifies that sample values
should be scaled to the full range of possible values at the
sample depth. However, the sBIT chunk is provided in order to
store the original number of significant bits ...
... Sub(x) = Raw(x) - Raw(x-bpp)
where x ranges from zero to the number of bytes representing the
scanline minus one, Raw(x) refers to the raw data byte at that
byte position in the scanline, and bpp is defined as the number of
...
... Up(x) = Raw(x) - Prior(x)
where x ranges from zero to the number of bytes representing the
scanline minus one, Raw(x) refers to the raw data byte at that
byte position in the scanline, and Prior(x) refers to the
...
... Average(x) = Raw(x) - floor((Raw(x-bpp)+Prior(x))/2)
where x ranges from zero to the number of bytes representing the
scanline minus one, Raw(x) refers to the raw data byte at that
byte position in the scanline, Prior(x) refers to the unfiltered
...
... Prior(x-bpp))
where x ranges from zero to the number of bytes representing the
scanline minus one, Raw(x) refers to the raw data byte at that
byte position in the scanline, Prior(x) refers to the unfiltered
...
... output = ROUND(input * MAXOUTSAMPLE / MAXINSAMPLE)
where the input samples range from 0 to MAXINSAMPLE and the
outputs range from 0 to MAXOUTSAMPLE (which is (2^sampledepth)-1).
...
... where the input samples range from 0 to MAXINSAMPLE and the
outputs range from 0 to MAXOUTSAMPLE (which is (2^sampledepth)-1).
A close approximation to the linear scaling method ...
... samples are being scaled up to 8 bits. If the source sample value
is 27 (in the range from 0-31), then the original bits are:
...
... image quality at the price of increasing file size.
In some applications the original source data may have a range
that is not a power of 2. The linear scaling equation still works
for this case, although the shifting methods ...
... recommended that an sBIT chunk not be written for such images,
since sBIT suggests that the original data range was exactly
0..2^S-1.
...
... A linear intensity level, expressed as a floating-point value in
the range 0 to 1, can be converted to a gamma-encoded sample value
by
...
... valid premultiplied data, the
sample values never exceed their corresponding alpha values, so
the result of the division should always be in the range 0 to 1.
If the alpha value is zero, output black (zeroes).
...
...
where alpha and the input and output sample values are expressed
as fractions in the range 0 to 1. This computation should be
performed with linear (non-gamma-encoded) sample values. For
color images ...
... output = input ^ gamma
where both input and output are scaled to the range 0 to 1.
Grayscale
...
... intensity range. An image gamma in the range 0.3 to 0.5
allocates sample values in a way that roughly corresponds to
the eye's response, so that 8 bits ...
... it is necessary to treat such images as having a file_gamma
value in the range 0.4-0.6, depending on the room lighting
level that the author was working in.
...
... power function.
By convention, "input" and "output" are both scaled to the range
0..1, with 0 representing black and 1 representing maximum white (or
red, etc). Normalized in this way, the power function is completely
...
... linear-sample image, we allocate fewer sample values to brighter
parts of the tonal range and more sample values to the darker
portions of the tonal range.
...
... parts of the tonal range and more sample values to the darker
portions of the tonal range.
Thus, for the same apparent image ...
... specific display condition. We are really using a power function
in the process of encoding an intensity range into a small integer
field, and so it is more correct to say "gamma encoded" samples
...
... Here we assume we are working with linear RGB floating point data
in the range 0..1. If the gamma is not 1.0, make it so on the
floating point data. Then convert source_RGB to XYZ by matrix
...
... on the destination device. The process of making the colors fit,
which can range from a simple clip to elaborate nonlinear scaling
transformations, is termed gamut mapping. The aim is to produce a
reasonable visual representation of the original image ...