EP0866608A2
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EP
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Method for correcting luminance gradation in an image pickup apparatus
Assignee: Panasonic Holdings Corp
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Filing: 1998-03-17
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Granted: —
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Expires: 2018-03-17
Abstract
Abstract A synthesized picture signal of a dynamic image is produced by combining a long-time picture signal representing a low luminance and a short-time picture signal representing a high luminance, pieces of histogram data corresponding to a plurality of luminance levels are detected from the synthesized picture signal, a sum of values of pieces of histogram data is repeatedly calculated as a summed value of a piece of summed histogram data while the number of pieces of histogram data is increased, and an inclination of a line indicated by a series of summed values is detected as a luminance gradation characteristic. Thereafter, the luminance gradation characteristic is corrected to a corrected luminance gradation characteristic according to a relationship between a maximum luminance level and an upper limit luminance level of a dynamic range, and a luminance gradation corrected signal composed of the pieces of histogram data corresponding to gradation corrected luminance levels is produced according to the corrected luminance gradation characteristic to make a maximum gradation corrected luminance level equal to or lower than the upper limit luminance level. Therefore, a low luminance object and/or a high luminance object can be clearly reproduced within the dynamic range.
Inventors
- 👤 Toshiyuki Sano
- 👤 Keiji Toyoda
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-09 11:47
CPC Classifications
H; H04; H04N; H04N23/00; H04N23/70; H04N23/73; H04N23/741; H04N23/76
Claims Analysis
Total Claims: 7
Claim 1
Independent Claim
226 words
A luminance gradation correcting method in an image pickup
apparatus having a dynamic range, comprising the steps of: detecting pieces of histogram data respectively indicating
the number of pixels of a luminance level from an input
picture signal produced in the image pickup apparatus, the
input picture signal indicating a particular image; detecting a maximum luminance level from the luminance
levels of the pieces of histogram data; detecting a luminance gradation characteristic of the
particular image indicated by the input picture signal from
the pieces of histogram data corresponding to the luminance
levels; producing a corrected luminance gradation characteristic of
the particular image from the luminance gradation
characteristic of the particular image according to the
maximum luminance level and the dynamic range of the image
pickup apparatus; correcting the luminance levels of the pieces of histogram
data to a plurality of gradation corrected luminance levels
according to the corrected luminance gradation characteristic
of the particular image to set the gradation corrected
luminance levels corresponding to the pieces of histogram data
within the dynamic range of the image pickup apparatus; and producing a luminance gradation corrected picture signal
composed of the pieces of histogram data corresponding to the
gradation corrected luminance levels to reproduce the
particular image, in which each of the pixels has one
corresponding gradation corrected luminance level, from the
luminance gradation corrected picture signal.
Claim 2
Dependent Claim
171 words
A luminance gradation correcting method according to claim
1 in which the step of producing a corrected luminance
gradation characteristic comprises the steps of: setting the corrected luminance gradation characteristic to
the luminance gradation characteristic in cases where the
maximum luminance level is lower than or equal to a standard
luminance level which is half an upper limit luminance value
of the dynamic range; setting the corrected luminance gradation characteristic to
make a maximum gradation corrected luminance level among the
gradation corrected luminance levels agree with the maximum
luminance level in cases where the maximum luminance level is
higher than the standard luminance level and is lower than or
equal to the upper limit luminance value of the dynamic range;
and setting the corrected luminance gradation characteristic to
make a maximum gradation corrected luminance level among the
gradation corrected luminance levels agree with the upper
limit luminance value of the dynamic range in cases where the
maximum luminance level is higher than the upper limit
luminance value of the dynamic range.
Claim 3
Dependent Claim
66 words
A luminance gradation correcting method according to
claim 1 or 2 in which the step of detecting a maximum
luminance level comprises the steps of: selecting one or more particular pieces of histogram data
respectively having a value not equal to zero from the
luminance levels; and detecting the maximum luminance level from one or more
luminance levels corresponding to the particular pieces of
histogram data.
Claim 4
Dependent Claim
133 words
A luminance gradation correcting method according to
claim 1, 2 or 3 in which the step of detecting a luminance
gradation characteristic comprises the steps of: repeatedly calculating a sum of values of pieces of
histogram data as a summed value of a piece of summed
histogram data while the number of pieces of histogram data is
increased one by one in the order of heightening a luminance
level corresponding to one piece of particular histogram data
added to the pieces of histogram data; and setting an inclination of a line indicated by the series of
summed values of the pieces of summed histogram data, which
are arranged in the order of increasing the number of pieces
of histogram data corresponding to each piece of summed
histogram data, as the luminance gradation characteristic.
Claim 5
Dependent Claim
280 words
A luminance gradation correcting method according to
claim 1, 2, 3 or 4 in which the step of detecting pieces of
histogram data comprises the steps of: detecting pieces of original histogram data respectively
indicating the number of pixels of one luminance level from
the input picture signal; preparing a limitation value in cases where the maximum
luminance level is lower than or equal to the standard
luminance level; preparing a low limitation value and an upper limitation
value higher than the low limitation value in cases where the
maximum luminance level is higher than the standard luminance
level; setting the pieces of original histogram data to the pieces
of histogram data having values equal to the limitation value
in cases where the maximum luminance level is lower than or
equal to the standard luminance level; setting each piece of original histogram data lower than
the low limitation value to one piece of histogram data having
a value equal to the low limitation value in cases where the
maximum luminance level is higher than the standard luminance
level; setting each piece of original histogram data higher than
the high limitation value to one piece of histogram data
having a value equal to the high limitation value in cases
where the maximum luminance level is higher than the standard
luminance level; and setting each piece of original histogram data equal to or
higher than the low limitation value and equal to or lower
than the high limitation value to one piece of histogram data
having the same value as that of the piece of original
histogram data in cases where the maximum luminance level is
higher than the standard luminance level.
Claim 6
Dependent Claim
104 words
A luminance gradation correcting method according to
claim 1, 2, 3, 4 or 5 in which the step of detecting pieces
of histogram data includes the steps of: producing a long-time picture signal indicating the
particular image in a long exposure time; producing a short-time picture signal indicating the
particular image in a short exposure time; and combining the long-time picture signal and the short-time
picture signal to produce the input picture signal in which an
image of a low luminance object is indicated by the long-time
picture signal and an image of a high luminance object is
indicated by the short-time picture signal.
Claim 7
Dependent Claim
18 words
An image pickup apparatus adapted to operate
according to the method of any one of the preceding claims.
References Cited (Backward Citations)
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