お知らせ:
2025 年 4 月 15 日より前に Earth Engine の使用を登録したすべての非商用プロジェクトは、Earth Engine へのアクセスを維持するために
非商用目的での利用資格を確認する必要があります。
ee.Image.expression
コレクションでコンテンツを整理
必要に応じて、コンテンツの保存と分類を行います。
画像に対して演算式を評価します。追加の画像が関与する可能性があります。
メイン入力画像のバンドは、組み込み関数 b() を使用して、b(0) または b('band_name') として使用できます。
式内の変数は、opt_map で指定する必要がある追加の画像パラメータとして解釈されます。このような各イメージのバンドには、image.band_name や image[0] のようにアクセスできます。
b() と image[] の両方で複数の引数を使用して、複数のバンドを指定できます（例: b(1, 'name', 3)）。引数なしで b() を呼び出すか、変数自体を使用すると、画像のすべてのバンドが返されます。
式の結果が単一のバンドの場合、'=' 演算子を使用して名前を割り当てることができます（例: x = a + b）。
指定された式で計算された画像を返します。
| 用途 | 戻り値 |
|---|
Image.expression(expression, map) | 画像 |
| 引数 | タイプ | 詳細 |
|---|
これ: image | 画像 | Image インスタンス。 |
expression | 文字列 | 評価する式。 |
map | Dictionary<Image>、省略可 | 名前で利用可能な入力画像のマップ。 |
例
コードエディタ（JavaScript）
// The following expressions calculate the normalized difference vegetation
// index (NDVI): (NIR - Red) / (NIR + Red).
// NIR is Landsat 8 L2 band 'SR_B5', the 4th band index.
// Red is Landsat 8 L2 band 'SR_B4', the 3rd band index.
// A Landsat 8 L2 surface reflectance image.
var img = ee.Image('LANDSAT/LC08/C02/T1_L2/LC08_044034_20210508');
// Visualization parameters for NDVI.
var ndviVis = {min: 0, max: 0.5};
// Expression using image band indices.
var bandIndexExp = '(b(4) - b(3)) / (b(4) + b(3))';
var bandIndexImg = img.expression(bandIndexExp).rename('NDVI');
Map.setCenter(-122.14, 37.38, 11);
Map.addLayer(bandIndexImg, ndviVis, 'NDVI 1');
// Expression using image band names.
var bandNameExp = '(b("SR_B5") - b("SR_B4")) / (b("SR_B5") + b("SR_B4"))';
var bandNameImg = img.expression(bandNameExp).rename('NDVI');
Map.addLayer(bandNameImg, ndviVis, 'NDVI 2');
// Expression using named variables.
var namedVarsExp = '(NIR - Red) / (NIR + Red)';
var namedVarsImg = ee.Image().expression({
expression: namedVarsExp,
map: {
NIR: img.select('SR_B5'),
Red: img.select('SR_B4')
}
}).rename('NDVI');
Map.addLayer(namedVarsImg, ndviVis, 'NDVI 3');
// Expression using named variables with image band access by dot notation.
var namedVarsDotExp = '(ls8.SR_B5 - ls8.SR_B4) / (ls8.SR_B5 + ls8.SR_B4)';
var namedVarsDotImg = ee.Image().expression({
expression: namedVarsDotExp,
map: {ls8: img}
}).rename('NDVI');
Map.addLayer(namedVarsDotImg, ndviVis, 'NDVI 4');
// Expressions can use arithmetic operators (+ - * / % **), relational
// operators (== != < > <= >=), logical operators (&& || ! ^), the ternary
// operator (condition ? ifTrue : ifFalse), and a subset of JavaScript Math
// functions. Math functions are called by name directly, they are not accessed
// from the Math object (e.g., sqrt() instead of Math.sqrt()).
var jsMathExp = 'c = sqrt(pow(a, 2) + pow(b, 2))';
var jsMathImg = ee.Image().expression({
expression: jsMathExp,
map: {
a: ee.Image(5),
b: img.select('SR_B2')
}
});
Map.addLayer(jsMathImg, {min: 5000, max: 20000}, 'Hypotenuse', false);
Python の設定
Python API とインタラクティブな開発での geemap の使用については、
Python 環境のページをご覧ください。
import ee
import geemap.core as geemap
Colab（Python）
# The following expressions calculate the normalized difference vegetation
# index (NDVI): (NIR - Red) / (NIR + Red).
# NIR is Landsat 8 L2 band 'SR_B5', the 4th band index.
# Red is Landsat 8 L2 band 'SR_B4', the 3rd band index.
# A Landsat 8 L2 surface reflectance image.
img = ee.Image('LANDSAT/LC08/C02/T1_L2/LC08_044034_20210508')
# Visualization parameters for NDVI.
ndvi_vis = {'min': 0, 'max': 0.5}
# Expression using image band indices.
band_index_exp = '(b(4) - b(3)) / (b(4) + b(3))'
band_index_img = img.expression(band_index_exp).rename('NDVI')
m = geemap.Map()
m.set_center(-122.14, 37.38, 11)
m.add_layer(band_index_img, ndvi_vis, 'NDVI 1')
# Expression using image band names.
band_name_exp = '(b("SR_B5") - b("SR_B4")) / (b("SR_B5") + b("SR_B4"))'
band_name_img = img.expression(band_name_exp).rename('NDVI')
m.add_layer(band_name_img, ndvi_vis, 'NDVI 2')
# Expression using named variables.
named_vars_exp = '(NIR - Red) / (NIR + Red)'
named_vars_img = (
ee.Image()
.expression(
expression=named_vars_exp,
opt_map={'NIR': img.select('SR_B5'), 'Red': img.select('SR_B4')},
)
.rename('NDVI')
)
m.add_layer(named_vars_img, ndvi_vis, 'NDVI 3')
# Expression using named variables with image band access by dot notation.
named_vars_dot_exp = '(ls8.SR_B5 - ls8.SR_B4) / (ls8.SR_B5 + ls8.SR_B4)'
named_vars_dot_img = (
ee.Image()
.expression(expression=named_vars_dot_exp, opt_map={'ls8': img})
.rename('NDVI')
)
m.add_layer(named_vars_dot_img, ndvi_vis, 'NDVI 4')
# Expressions can use arithmetic operators (+ - * / % **), relational
# operators (== != < > <= >=), logical operators (&& || ! ^), the ternary
# operator (condition ? ifTrue : ifFalse), and a subset of JavaScript Math
# functions. Math functions are called by name directly, they are not accessed
# from the Math object (e.g., sqrt() instead of Math.sqrt()).
js_math_exp = 'c = sqrt(pow(a, 2) + pow(b, 2))'
js_math_img = ee.Image().expression(
expression=js_math_exp, opt_map={'a': ee.Image(5), 'b': img.select('SR_B2')}
)
m.add_layer(js_math_img, {'min': 5000, 'max': 20000}, 'Hypotenuse', False)
m
特に記載のない限り、このページのコンテンツはクリエイティブ・コモンズの表示 4.0 ライセンスにより使用許諾されます。コードサンプルは Apache 2.0 ライセンスにより使用許諾されます。詳しくは、Google Developers サイトのポリシーをご覧ください。Java は Oracle および関連会社の登録商標です。
最終更新日 2025-07-25 UTC。
[null,null,["最終更新日 2025-07-25 UTC。"],[[["\u003cp\u003e\u003ccode\u003eImage.expression()\u003c/code\u003e allows you to perform arithmetic calculations on images using expressions.\u003c/p\u003e\n"],["\u003cp\u003eYou can access image bands within the expression using \u003ccode\u003eb()\u003c/code\u003e with band indices or names, or by defining variables representing images.\u003c/p\u003e\n"],["\u003cp\u003eExpressions can incorporate arithmetic, relational, logical, and ternary operators, along with select JavaScript Math functions.\u003c/p\u003e\n"],["\u003cp\u003eNamed variables representing images can be used in the expression, and accessed by their names or through dot notation if they represent images.\u003c/p\u003e\n"],["\u003cp\u003eThe expression's result is a new image which can be assigned a name using the '=' operator if it is single-banded.\u003c/p\u003e\n"]]],[],null,["# ee.Image.expression\n\n\u003cbr /\u003e\n\nEvaluates an arithmetic expression on an image, possibly involving additional images.\n\n\u003cbr /\u003e\n\nThe bands of the primary input image are available using the built-in function b(), as b(0) or b('band_name').\n\nVariables in the expression are interpreted as additional image parameters which must be supplied in opt_map. The bands of each such image can be accessed like image.band_name or image\\[0\\].\n\nBoth b() and image\\[\\] allow multiple arguments, to specify multiple bands, such as b(1, 'name', 3). Calling b() with no arguments, or using a variable by itself, returns all bands of the image.\n\nIf the result of an expression is a single band, it can be assigned a name using the '=' operator (e.g.: x = a + b).\n\nReturns the image computed by the provided expression.\n\n| Usage | Returns |\n|-----------------------------------------|---------|\n| Image.expression`(expression, `*map*`)` | Image |\n\n| Argument | Type | Details |\n|---------------|-------------------------------|------------------------------------------|\n| this: `image` | Image | The Image instance. |\n| `expression` | String | The expression to evaluate. |\n| `map` | Dictionary\\\u003cImage\\\u003e, optional | A map of input images available by name. |\n\nExamples\n--------\n\n### Code Editor (JavaScript)\n\n```javascript\n// The following expressions calculate the normalized difference vegetation\n// index (NDVI): (NIR - Red) / (NIR + Red).\n// NIR is Landsat 8 L2 band 'SR_B5', the 4th band index.\n// Red is Landsat 8 L2 band 'SR_B4', the 3rd band index.\n\n// A Landsat 8 L2 surface reflectance image.\nvar img = ee.Image('LANDSAT/LC08/C02/T1_L2/LC08_044034_20210508');\n\n// Visualization parameters for NDVI.\nvar ndviVis = {min: 0, max: 0.5};\n\n// Expression using image band indices.\nvar bandIndexExp = '(b(4) - b(3)) / (b(4) + b(3))';\nvar bandIndexImg = img.expression(bandIndexExp).rename('NDVI');\nMap.setCenter(-122.14, 37.38, 11);\nMap.addLayer(bandIndexImg, ndviVis, 'NDVI 1');\n\n// Expression using image band names.\nvar bandNameExp = '(b(\"SR_B5\") - b(\"SR_B4\")) / (b(\"SR_B5\") + b(\"SR_B4\"))';\nvar bandNameImg = img.expression(bandNameExp).rename('NDVI');\nMap.addLayer(bandNameImg, ndviVis, 'NDVI 2');\n\n// Expression using named variables.\nvar namedVarsExp = '(NIR - Red) / (NIR + Red)';\nvar namedVarsImg = ee.Image().expression({\n expression: namedVarsExp,\n map: {\n NIR: img.select('SR_B5'),\n Red: img.select('SR_B4')\n }\n}).rename('NDVI');\nMap.addLayer(namedVarsImg, ndviVis, 'NDVI 3');\n\n// Expression using named variables with image band access by dot notation.\nvar namedVarsDotExp = '(ls8.SR_B5 - ls8.SR_B4) / (ls8.SR_B5 + ls8.SR_B4)';\nvar namedVarsDotImg = ee.Image().expression({\n expression: namedVarsDotExp,\n map: {ls8: img}\n}).rename('NDVI');\nMap.addLayer(namedVarsDotImg, ndviVis, 'NDVI 4');\n\n// Expressions can use arithmetic operators (+ - * / % **), relational\n// operators (== != \u003c \u003e \u003c= \u003e=), logical operators (&& || ! ^), the ternary\n// operator (condition ? ifTrue : ifFalse), and a subset of JavaScript Math\n// functions. Math functions are called by name directly, they are not accessed\n// from the Math object (e.g., sqrt() instead of Math.sqrt()).\nvar jsMathExp = 'c = sqrt(pow(a, 2) + pow(b, 2))';\nvar jsMathImg = ee.Image().expression({\n expression: jsMathExp,\n map: {\n a: ee.Image(5),\n b: img.select('SR_B2')\n }\n});\nMap.addLayer(jsMathImg, {min: 5000, max: 20000}, 'Hypotenuse', false);\n```\nPython setup\n\nSee the [Python Environment](/earth-engine/guides/python_install) page for information on the Python API and using\n`geemap` for interactive development. \n\n```python\nimport ee\nimport geemap.core as geemap\n```\n\n### Colab (Python)\n\n```python\n# The following expressions calculate the normalized difference vegetation\n# index (NDVI): (NIR - Red) / (NIR + Red).\n# NIR is Landsat 8 L2 band 'SR_B5', the 4th band index.\n# Red is Landsat 8 L2 band 'SR_B4', the 3rd band index.\n\n# A Landsat 8 L2 surface reflectance image.\nimg = ee.Image('LANDSAT/LC08/C02/T1_L2/LC08_044034_20210508')\n\n# Visualization parameters for NDVI.\nndvi_vis = {'min': 0, 'max': 0.5}\n\n# Expression using image band indices.\nband_index_exp = '(b(4) - b(3)) / (b(4) + b(3))'\nband_index_img = img.expression(band_index_exp).rename('NDVI')\nm = geemap.Map()\nm.set_center(-122.14, 37.38, 11)\nm.add_layer(band_index_img, ndvi_vis, 'NDVI 1')\n\n# Expression using image band names.\nband_name_exp = '(b(\"SR_B5\") - b(\"SR_B4\")) / (b(\"SR_B5\") + b(\"SR_B4\"))'\nband_name_img = img.expression(band_name_exp).rename('NDVI')\nm.add_layer(band_name_img, ndvi_vis, 'NDVI 2')\n\n# Expression using named variables.\nnamed_vars_exp = '(NIR - Red) / (NIR + Red)'\nnamed_vars_img = (\n ee.Image()\n .expression(\n expression=named_vars_exp,\n opt_map={'NIR': img.select('SR_B5'), 'Red': img.select('SR_B4')},\n )\n .rename('NDVI')\n)\nm.add_layer(named_vars_img, ndvi_vis, 'NDVI 3')\n\n# Expression using named variables with image band access by dot notation.\nnamed_vars_dot_exp = '(ls8.SR_B5 - ls8.SR_B4) / (ls8.SR_B5 + ls8.SR_B4)'\nnamed_vars_dot_img = (\n ee.Image()\n .expression(expression=named_vars_dot_exp, opt_map={'ls8': img})\n .rename('NDVI')\n)\nm.add_layer(named_vars_dot_img, ndvi_vis, 'NDVI 4')\n\n# Expressions can use arithmetic operators (+ - * / % **), relational\n# operators (== != \u003c \u003e \u003c= \u003e=), logical operators (&& || ! ^), the ternary\n# operator (condition ? ifTrue : ifFalse), and a subset of JavaScript Math\n# functions. Math functions are called by name directly, they are not accessed\n# from the Math object (e.g., sqrt() instead of Math.sqrt()).\njs_math_exp = 'c = sqrt(pow(a, 2) + pow(b, 2))'\njs_math_img = ee.Image().expression(\n expression=js_math_exp, opt_map={'a': ee.Image(5), 'b': img.select('SR_B2')}\n)\nm.add_layer(js_math_img, {'min': 5000, 'max': 20000}, 'Hypotenuse', False)\nm\n```"]]
