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"cells": [
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Using parameters `norm`, `vmain`, `vmax` in `geomImshow()`\n",
"\n",
"You can use parameters `norm`, `vmain`, `vmax` when rendering grayscale images.\n",
"\n",
"A grayscale image is specified by 2D array where each element's value \n",
"represents the luminance of corresponding pixel in the image."
]
},
{
"cell_type": "code",
"execution_count": 1,
"metadata": {
"execution": {
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"source": [
"%useLatestDescriptors\n",
"%use lets-plot"
]
},
{
"cell_type": "code",
"execution_count": 2,
"metadata": {
"execution": {
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{
"data": {
"text/plain": [
"Lets-Plot Kotlin API v.4.12.0. Frontend: Notebook with dynamically loaded JS. Lets-Plot JS v.4.8.1.\n",
"Outputs: Web (HTML+JS), Kotlin Notebook (Swing), Static SVG (hidden)"
]
},
"execution_count": 2,
"metadata": {},
"output_type": "execute_result"
}
],
"source": [
"LetsPlot.getInfo()"
]
},
{
"cell_type": "code",
"execution_count": 3,
"metadata": {
"execution": {
"iopub.execute_input": "2025-12-03T16:08:14.958693Z",
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"source": [
"// Generate 2D arrays. \n",
"// First two arrays both contain float numbers but have different range of values.\n",
"// The 3rd array contains int-s.\n",
"fun linspace(start: Double, end: Double, count: Int): List {\n",
" val step = (end - start) / (count - 1)\n",
" return mutableListOf() + \n",
" start + (1 .. (count - 2)).map { i -> start + i * step } + end\n",
"}\n",
"\n",
"val arr_f0 = RasterData.create(listOf(linspace(0.3, 0.7, 30)))\n",
"val arr_f1 = RasterData.create(listOf(linspace(30.0, 170.0, 30)))\n",
"val arr_i = RasterData.create(listOf(linspace(30.0, 170.0, 30).map { it.toInt() }))"
]
},
{
"cell_type": "code",
"execution_count": 4,
"metadata": {
"execution": {
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"shell.execute_reply": "2025-12-03T16:08:15.292255Z"
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},
"outputs": [],
"source": [
"// Setup suitable plot options for the demo.\n",
"val p = (letsPlot() + ggsize(450, 60) + geomRect(xmin=-0.5, ymin=-0.5, xmax=29.5, ymax=0.5, color=\"black\", alpha=0) + \n",
"coordCartesian() + themeClassic() + theme(axis=\"blank\"))"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"#### Image normalization\n",
"\n",
"By default, `geomImshow()` applies a linear scaling to transform data values to range [0-255]."
]
},
{
"cell_type": "code",
"execution_count": 5,
"metadata": {
"execution": {
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"shell.execute_reply": "2025-12-03T16:08:15.417303Z"
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"data": {
"text/html": [
" \n",
" "
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{
"data": {
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" \n",
" "
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},
"metadata": {},
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],
"source": [
"(p + geomImshow(arr_f0)).show()\n",
"(p + geomImshow(arr_f1)).show()\n",
"(p + geomImshow(arr_i)).show()"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## \n",
"\n",
"You can disable image normalization using the `norm` parameter."
]
},
{
"cell_type": "code",
"execution_count": 6,
"metadata": {
"execution": {
"iopub.execute_input": "2025-12-03T16:08:15.419343Z",
"iopub.status.busy": "2025-12-03T16:08:15.419187Z",
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"shell.execute_reply": "2025-12-03T16:08:15.456719Z"
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"outputs": [
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"data": {
"text/html": [
" \n",
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],
"source": [
"(p + geomImshow(arr_f0, norm=false)).show()\n",
"(p + geomImshow(arr_f1, norm=false)).show()\n",
"(p + geomImshow(arr_i, norm=false)).show()"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"#### Define normalization range using `vmin, vmax` parameters"
]
},
{
"cell_type": "code",
"execution_count": 7,
"metadata": {
"execution": {
"iopub.execute_input": "2025-12-03T16:08:15.457896Z",
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"shell.execute_reply": "2025-12-03T16:08:15.496065Z"
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"source": [
"// Set upper limit less than the data max value.\n",
"(p + geomImshow(arr_f0, vmax=.5)).show()\n",
"(p + geomImshow(arr_f1, vmax=100)).show()\n",
"(p + geomImshow(arr_i, vmax=100)).show()"
]
},
{
"cell_type": "code",
"execution_count": 8,
"metadata": {
"execution": {
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"source": [
"// Set limits wider than the data entire range.\n",
"(p + geomImshow(arr_f0, vmin=.4, vmax=.6)).show()\n",
"(p + geomImshow(arr_f1, vmin=70, vmax=120)).show()\n",
"(p + geomImshow(arr_i, vmin=50, vmax=150)).show()"
]
}
],
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