




版权说明:本文档由用户提供并上传,收益归属内容提供方,若内容存在侵权,请进行举报或认领
文档简介
数字图像处理-图像的表达Sampling&Quantisation采样和量化• 采样时要确定好空间分辨率,即DP
I• 量化时要确定好灰度分辨率,將采样影像转换为数值的过程称为量化。例如,白色是转化为“1”和黑色則转化为“0”。Digital
Image
AcquisitionA physical image, which may be visible orinvisible
to
the
human
eye,
is
normally
a
continuous-tone image with
various shades
blended togethersmoothly having no disruptions. Acquisition of adigital
image
from
a
continuous-tone
image
requiresdigitization
of
spatial
coordinates(Known
as
sampling)and
digitization
of
brightness(Known
as
quantisation).Image
DigitiserConsequently,
an
image
digitiserconsists
of
five
elements:Sampling
aperture
to
allow
the
digitiser
to
access
image
elementsindividuallyScanning
mechanism
to
move
the
sampling
aperture
over
the
image
ins
predetermined
patternLight
sensor
to
measure
the
brightness
of
the
image
at
each
pixelthrough
the
sampling
apertureA/D
converter
to
convert
the
continuous
output
of
the
light
sensor
intoan
integer
valueMemory
to
store
the
gray-level
values
produced
by
the
A/D
converterSamplingandSpatialResolution4If
a
continuous-tone
image
is
approximated
bya
N
lines*M
pixels
digital
image,thenit
requires
decisions
about
values
forN
and
M.
In
practice,N
and
M
arepredetermined
dueto
thelimited
choice
of
available
camerasandimage
acquisition
hardware
and
are
normallyset
to
integerpowers
of
2.As
N
and
M
are
decreased,the
number
of
pixels
in
a
digitalimage
decreased
rapidlygiving
worseapproximation
of
the
originalimage
dueto
lowerspatial
resolutionSamplingandSpatialResolutionHowever,for
a
given
application,
selecting
the
minimum
resolution
necessary
cansignificantly
reduce
storage
and
processing
requirements.
According
to
the
classicalsampling
theorem,
an
image
mustbe
sampled
at
a
rate
atleasttwice
as
fast
as
the
highest
spatial
frequency
(the
frequency
at
which
brightness
cycle
from
dark
to
light
andback
to
dark)
contained
in
theimage.Original
Image
LineSampled
at
a
rate
lessthanhalf
the
spatialfrequencyUndersampledImage
LineSpatial
aliasing
occurswiththe
high
frequency
detailbeing
translatedtoa
lowfrequency
due
to
some
of
itstransitionsare
missedIn
the
selection
of
a
suitable
spatial
resolution,
the
display-observer
distance
is
anotherfactor
for
consideration.As
the
distance
between
animage
and
observer
doublescorrespondingto
a
reduction
of
theimage
size
byon-half,
the
spatial
resolution
can
be
decreased
byon-halfwithout
causing
anyspatial
detail
loss
for
the
observer.Correctly
SampledImage
LineSampled
at
a
rate
2
times
thespatial
frequencyQuantisationandBrightnessResolutionIf
the
intensity
of
a
continuous-tone
image
ata
samplingpoint
isquantised
toaninteger
value
calledthe
gray-level,
thenthe
accuracy
of
the
gray-level
assigneddepends
on
the
numberofbitsusedtorepresent
the
number
of
gray-levels
in
animage.Asthe
number
ofbitsare
decreased,the
imageappearscoarser
due
tolower
brightnessresolutionwithaninsufficient
number
of
gray-levels
insmoothareas
of
theimage.Ex001.mLike
spatialresolution,
the
brightness
resolutionalso
dependsonimage-observer
distance.
Thesmaller
the
imageasitis
placedfurtheraway
from
theobserver,
the
lower
brightness
resolutionneeds
tobe.BrightnessResolution
分辨率• 電腦顯示器的解析度大約為
72dp
i
,印表機是從150
到1440dp
i
(高解析度機種)
,而掃瞄器的解析度是300dp
i
或更高。Pos
t
sc
r
i
p
t
的印表機使用一種解析度衡量方式,稱為每英吋線數(
l
p
i
),意思是指每一英吋中可以畫入的線條數量。這種方式的影用是基於要把半色調影像,例如相片,分解成點(
或圖素)
。在過去,這種半色調的顯示是由不同寬度的直線構成。在近年,轉變成以格子的方式來呈現,因此可以把影像分裂成點,每英吋線數的方式也就不適用了。報紙有
60
lpi的解析度,而雜誌有133-175
lpi的解析度。高品質的印刷原料可能會超過
200lpi。DigitalImageRepresentationA
digital
image
is
represented
mathematically
bythe
function
f(x,y),
where
x
and
y
areindependent
variables
denoting
spatialco-ordinates,and
the
value
of
fatspatial
co-ordinates
(x,y)
gives
the
intensityof
the
image
atthatpoint.
However,
there
are
threedifferent
spatialco-ordinate
systems
being
used
in
digitalimage
processing:Cartesian
co-ordinate
systemMatrix
co-ordinate
systemPixel
co-ordinate
systemxy0 12 3 4210xy12 3 4 5123111
2 3 4 51 0 1 1 1 02
0 1 0 3 1 0 111ColumnRowOriginalPixel8DigitalImageRepresentationinMatlab9Matlab
uses
a
rectangular
matrix
(two-dimensional
array)
to
represent
adigital
image.
There
are
four
basic
types
of
images
supported
by
Matlab,namely,intensity
(gray-level)
images,
binary
images,
RGB
imagesandindexed
images.IntensityImages
(Gray-ScaleImages)10Matlab
uses
a
single
matrix
to
represent
an
intensity
image
with
the
magnitude
value
ofeach
element
inthe
matrix
corresponding
tothe
gray-level
of
each
pixel
in
the
image.Two
differentdata
types
are
available
in
Matlab
to
represent
the
gray-level:double(double
precision):
the
gray-level
values
rang
from
0
(corresponding
to
black)
to
1
(corresponding
to
white),
and
it
is
used
forperforming
mathematical
operations.uint8(unsigned
8
bit
integers):
the
gray-level
values
range
from
0
(corresponding
to
black)
to
255(corresponding
to
white),
and
it
is
used
to
save
memory
as
it
requires
only1/8
the
memory
for
a
double
precision
array
(no
mathematical
operations
are
defined
forthis
data
type).Actual
gray-level
0
128
192
255
In
uint8
formatNormalised
gray-level00.5020
0.7529
1In
double
formatGray-ScaleImages11BinaryImagesMatlab
used
asingle
matrix
to
represent
a
binary
image
(aspecial
kind
ofintensity
image)
with
the
magnitude
valued
ofeach
element
in
the
matrixbeing
either
0
(black)
or
1(white).Binary
Image12Gray-ScaleImage13RGBImagesAll
colours
can
formed
by
various
combination
of
the
three
primary
colours,namely,
red(R),
green(G)
and
blue(B).In
Matlab,a
colour
image
isrepresented
by
three
separate
matriceswith
thesame
row
and
column
dimensions
to
represent
the
corresponding
red,
greenand
blue
components.0
.
75
0
.50
1 0 0 1 1 0 0
.50
0
01101010
.50010110
.50Red
Matrix 255002552550128255Green
Matrix025502550255128192
Blue
Matrix 002550255255128128
RGBImages14IndexedImages15In
the
indexed
image
representation,
Matlab
used
two
matrices,namely,
acolour
map
matrix
and
an
image
matrix,
to
represent
a
colour
image.
Thecolour
map
matrix
is
a
look-up
table
(LUT)
containing
n-row
by
3-columnelements,where
n
rowsspecify
the
number
of
possible
coloursand
3
columnsspecify
the
intensity
of
the
red,
green
and
blue
components
of
each
colour
(theintensity
of
each
colour
isspecified
on
the
interval
form
0
to
1).
The
value
ofeach
element
inthe
image
matrix
isused
as
an
index
to
look
up
the
desiredcolour
in
the
colour
map
for
each
image
pixel.
8 7 6 5 41 2 3 4 5G0101010.5020 0.5020
70.7925 0.5020
8B00
21
30 1
51
6
4Row
110.5020R100110ColorMap
MatrixImage
MatrixColor
ImageTutorialProblems(a)
For
digital
image
with
512x1024
pixels,
plot
the
memory
requirements
against
the
number
of
bits(from
1to
8)
usedtorepresent
a
pixel
value.If
c
computer
has
an
available
memory
of
1Mbyte,
determine
the
number
of
images
which
can
bestoredat
differentresolutions.(a)A
1024x1024
digita
温馨提示
- 1. 本站所有资源如无特殊说明,都需要本地电脑安装OFFICE2007和PDF阅读器。图纸软件为CAD,CAXA,PROE,UG,SolidWorks等.压缩文件请下载最新的WinRAR软件解压。
- 2. 本站的文档不包含任何第三方提供的附件图纸等,如果需要附件,请联系上传者。文件的所有权益归上传用户所有。
- 3. 本站RAR压缩包中若带图纸,网页内容里面会有图纸预览,若没有图纸预览就没有图纸。
- 4. 未经权益所有人同意不得将文件中的内容挪作商业或盈利用途。
- 5. 人人文库网仅提供信息存储空间,仅对用户上传内容的表现方式做保护处理,对用户上传分享的文档内容本身不做任何修改或编辑,并不能对任何下载内容负责。
- 6. 下载文件中如有侵权或不适当内容,请与我们联系,我们立即纠正。
- 7. 本站不保证下载资源的准确性、安全性和完整性, 同时也不承担用户因使用这些下载资源对自己和他人造成任何形式的伤害或损失。
最新文档
- 2025年5G网络通信设备采购合同标准
- 2025年醋酸乙烯酯项目建议书
- 2025年掺混肥项目合作计划书
- 2025年本地网传输系统项目合作计划书
- 强化法治教育促进遵纪守法计划
- 学习困难学生支持方案计划
- 水库管理与调度方案计划
- 选择合适的理财工具计划
- 2025年金属门窗及类似制品项目发展计划
- 2025年中国显控系统行业供需态势、竞争格局及投资前景分析报告(智研咨询)
- NB/T 11526-2024煤矿微震监测系统通用技术条件
- 2025年福建长汀金龙稀土有限公司招聘笔试参考题库含答案解析
- 2024年济南护理职业学院高职单招职业技能测验历年参考题库(频考版)含答案解析
- 四川省绵阳市2025届高三第二次诊断性考试英语试题(含答案无听力原文及音频)
- 贵州省贵阳市普通中学2024-2025学年高二上学期期末监测历史试题(含答案)
- 2025年八省适应性 历史试卷(西北卷)
- Python金融数据挖掘与分析实战课程教案教学教案
- 《企业偿债能力存在的问题及优化建议:以S地产公司为例》9500字(论文)
- 2025年上半年水利部长江水利委员会事业单位招聘68人(湖北武汉)重点基础提升(共500题)附带答案详解
- (2024)云南省公务员考试《行测》真题及答案解析
- 地方政府专项发债项目培训课件
评论
0/150
提交评论