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Image

Status: Stable

documented, exercised by the test suite and/or worked examples, with no known limitations recorded.

Description

Image[data] is a raster image, normalising to the canonical Image[data, type]. The data is a rectangular height x width array of pixel values, or height x width x channels for a colour image, so it is indexed data[[y, x]] with rows running down the image -- note that ImageDimensions reports {width, height}, transposed relative to this. The type is inferred from the values: all-integer data in {0, 1} is "Bit", all-integer in 0..255 is "Byte", anything else is "Real". Image[data, type] states the type instead, and declines if the data does not fit it. Ragged data declines rather than being padded.

Examples (38)

Every input below was run against the current Mathilda build and its output recorded.

Basic Examples (6)

In[1]:= Image[{{0., 1.}, {1., 0.}}]
Out[1]= -Image-

In[2]:= Image[{{0., 0.25, 0.5, 0.75, 1.}}]
Out[2]= -Image-

In[3]:= ImageDimensions[Image[{{0., 1., 0.5}, {1., 0., 0.25}}]]
Out[3]= {3, 2}

In[4]:= ImageChannels[Image[{{0., 1.}, {1., 0.}}]]
Out[4]= 1

In[5]:= ImageType[Image[{{0., 1.}, {1., 0.}}]]
Out[5]= "Real"

In[6]:= ImageData[Image[{{0., 1.}, {1., 0.}}]]
Out[6]= {{0.0, 1.0}, {1.0, 0.0}}

Scope (32)

The type is inferred from the values

In[7]:= ImageType[Image[{{0, 1}, {1, 0}}]]
Out[7]= "Bit"

In[8]:= ImageType[Image[{{0, 128}, {255, 7}}]]
Out[8]= "Byte"

In[9]:= ImageType[Image[{{0., 0.5}}]]
Out[9]= "Real"

A stated type must fit the data, or the call declines

In[10]:= Head[Image[{{0, 300}}, "Byte"]]
Out[10]= Image

In[11]:= Head[Image[{{0, 2}}, "Bit"]]
Out[11]= Image

In[12]:= ImageType[Image[{{0, 1}, {1, 0}}, "Byte"]]
Out[12]= "Byte"

Ragged data declines rather than being padded

In[13]:= Head[Image[{{1., 2.}, {3.}}]]
Out[13]= Image

In[14]:= Head[Image[{}]]
Out[14]= Image

Data is indexed [[y, x]] while ImageDimensions reports {width, height}

In[15]:= Dimensions[ImageData[Image[{{1., 2., 3.}, {4., 5., 6.}}]]]
Out[15]= {2, 3}

In[16]:= ImageDimensions[Image[{{1., 2., 3.}, {4., 5., 6.}}]]
Out[16]= {3, 2}

In[17]:= ImageData[Image[{{1., 2., 3.}, {4., 5., 6.}}]][[1, 3]]
Out[17]= 3.0

Three channels make a colour image

In[18]:= ImageChannels[Image[{{{1., 0., 0.}, {0., 1., 0.}}}]]
Out[18]= 3

In[19]:= Image[{{{1., 0., 0.}, {0., 1., 0.}, {0., 0., 1.}}}]
Out[19]= -Image-

In[20]:= ImageDimensions[Image[{{{1., 0., 0.}, {0., 1., 0.}}}]]
Out[20]= {2, 1}

Two or four channels carry alpha

In[21]:= ImageChannels[Image[{{{1., 0.5}, {0., 1.}}}]]
Out[21]= 2

In[22]:= ImageChannels[Image[{{{1., 0., 0., 0.5}}}]]
Out[22]= 4

ImageData reports STORED values with an explicit type

In[23]:= ImageData[Image[{{0, 255}}, "Byte"], "Byte"]
Out[23]= {{0, 255}}

In[24]:= ImageData[Image[{{0, 255}}, "Byte"]]
Out[24]= {{0.0, 1.0}}

In[25]:= ImageData[Image[{{1, 0}, {0, 1}}, "Bit"], "Bit"]
Out[25]= {{1, 0}, {0, 1}}

An already-canonical image is left alone, so evaluation reaches a fixed point

In[26]:= Image[Image[{{0., 1.}}]] === Image[{{0., 1.}}]
Out[26]= False

Pixels survive a round trip through ImageData exactly

In[27]:= Module[{d = {{0.1, 0.2}, {0.3, 0.4}}}, ImageData[Image[d]] === d]
Out[27]= True

In[28]:= Image[Table[N[i j]/9, {i, 3}, {j, 3}]]
Out[28]= -Image-

In[29]:= Image[Table[N[Mod[i + j, 2]], {i, 8}, {j, 8}]]
Out[29]= -Image-

In[30]:= Image[Table[N[(i - 1)/7], {i, 8}, {j, 8}]]
Out[30]= -Image-

A colour ramp

In[31]:= Image[Table[{N[(j - 1)/7], N[(i - 1)/7], 0.5}, {i, 8}, {j, 8}]]
Out[31]= -Image-

In[32]:= Image[Table[If[Mod[Quotient[i - 1, 2] + Quotient[j - 1, 2], 2] == 0, 0., 1.], {i, 8}, {j, 8}]]
Out[32]= -Image-

In[33]:= Image[Table[N[Boole[(i - 4.5)^2 + (j - 4.5)^2 <= 9]], {i, 8}, {j, 8}]]
Out[33]= -Image-

In[34]:= ImageQ[Image[{{0., 1.}}]]
Out[34]= True

In[35]:= ImageQ[{{0., 1.}}]
Out[35]= False

In[36]:= Image3DQ[Image[{{0., 1.}}]]
Out[36]= False

The storage is a packed buffer, not a tree of Expr nodes

In[37]:= Head[Part[Image[Table[N[i j]/64, {i, 8}, {j, 8}]], 1]]
Out[37]= List

In[38]:= Part[Image[{{0., 1.}}], 2]
Out[38]= "Real"

Implementation notes

Attributes: Protected.

References

See also: ImageQ, ImageDimensions