Skip to content

ColorConvert

Status: Stable

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

Description

ColorConvert[image, "Grayscale"] (or "Gray") reduces an image or an Image3D to a single channel using the Rec. 601 luminance weights 0.299 R + 0.587 G + 0.114 B, the same weights every filter here uses when it needs brightness. An image that is ALREADY GREY is returned unchanged, bit for bit, since no weighting happens. An image whose three channels are merely EQUAL is returned only to within an ulp, and whether it is exact depends on the value: those weights sum to 0.9999999999999999 when added in the order they are applied, though to exactly 1.0 in any order beginning with 0.114, so the final rounding lands on the input for some values and one ulp below it for others. The weights are the standard's and are not adjusted to compensate; a triple hand-tuned to sum to exactly 1.0 in double would no longer be Rec. 601.

Examples (30)

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

Basic Examples (6)

In[1]:= ImageData[ColorConvert[Image[{{{1., 0., 0.}, {0., 1., 0.}}}], "Grayscale"]]
Out[1]= {{0.299, 0.587}}

In[2]:= rgb = Image[Table[{N[i/16], N[j/16], 0.5}, {i, 1, 16}, {j, 1, 16}], "Real"];

In[3]:= sky = Image[Table[{N[0.15 + 0.7 (16 - i)/16], N[0.35 + 0.45 (16 - i)/16], N[0.85 - 0.35 (16 - i)/16]}, {i, 1, 16}, {j, 1, 24}], "Real"];

In[4]:= ColorConvert[rgb, "Grayscale"]
Out[4]= -Image-

In[5]:= ImageChannels[ColorConvert[rgb, "Grayscale"]]
Out[5]= 1

In[6]:= ColorConvert[sky, "Grayscale"]
Out[6]= -Image-

Scope (13)

In[7]:= chk = Image[Table[If[Mod[Quotient[i - 1, 2] + Quotient[j - 1, 2], 2] == 0, 0., 1.], {i, 1, 16}, {j, 1, 16}], "Real"];

In[8]:= zone = Image[Table[N[(1 + Cos[((i - 16)^2 + (j - 16)^2)/40.])/2], {i, 1, 32}, {j, 1, 32}], "Real"];

In[9]:= rgb = Image[Table[{N[i/16], N[j/16], 0.5}, {i, 1, 16}, {j, 1, 16}], "Real"];

In[10]:= sky = Image[Table[{N[0.15 + 0.7 (16 - i)/16], N[0.35 + 0.45 (16 - i)/16], N[0.85 - 0.35 (16 - i)/16]}, {i, 1, 16}, {j, 1, 24}], "Real"];

In[11]:= byte = Image[Table[Mod[i*13 + j*7, 256], {i, 1, 16}, {j, 1, 16}]];

In[12]:= vol = Image3D[Table[N[Mod[z*7 + y*13 + x*3, 97]]/97, {z, 1, 8}, {y, 1, 10}, {x, 1, 12}], "Real"];

In[13]:= ColorConvert[chk, "Grayscale"]
Out[13]= -Image-

In[14]:= ColorConvert[zone, "Grayscale"]
Out[14]= -Image-

In[15]:= ColorConvert[byte, "Grayscale"]
Out[15]= -Image-

In[16]:= ColorConvert[vol, "Grayscale"]
Out[16]= -Image-

In[17]:= ColorConvert[rgb, "Gray"]
Out[17]= -Image-

In[18]:= ImageChannels[ColorConvert[sky, "Grayscale"]]
Out[18]= 1

In[19]:= ImageDimensions[ColorConvert[rgb, "Grayscale"]]
Out[19]= {16, 16}

Applications (4)

In[20]:= rgb = Image[Table[{N[i/16], N[j/16], 0.5}, {i, 1, 16}, {j, 1, 16}], "Real"];

In[21]:= sky = Image[Table[{N[0.15 + 0.7 (16 - i)/16], N[0.35 + 0.45 (16 - i)/16], N[0.85 - 0.35 (16 - i)/16]}, {i, 1, 16}, {j, 1, 24}], "Real"];

In[22]:= EdgeDetect[ColorConvert[sky, "Grayscale"]]
Out[22]= -Image-

In[23]:= Binarize[ColorConvert[rgb, "Grayscale"]]
Out[23]= -Image-

Properties & Relations (5)

In[24]:= chk = Image[Table[If[Mod[Quotient[i - 1, 2] + Quotient[j - 1, 2], 2] == 0, 0., 1.], {i, 1, 16}, {j, 1, 16}], "Real"];

In[25]:= rgb = Image[Table[{N[i/16], N[j/16], 0.5}, {i, 1, 16}, {j, 1, 16}], "Real"];

In[26]:= ImageData[ColorConvert[chk, "Grayscale"]] === ImageData[chk]
Out[26]= True

In[27]:= ImageData[ColorConvert[rgb, "Gray"]] === ImageData[ColorConvert[rgb, "Grayscale"]]
Out[27]= True

In[28]:= ImageChannels[ColorConvert[rgb, "Grayscale"]] === 1
Out[28]= True

Neat Examples (2)

In[29]:= zone = Image[Table[N[(1 + Cos[((i - 16)^2 + (j - 16)^2)/40.])/2], {i, 1, 32}, {j, 1, 32}], "Real"];

In[30]:= ColorConvert[zone, "Grayscale"]
Out[30]= -Image-

Implementation notes

Attributes: Protected.

References