{
"cells": [
{
"cell_type": "markdown",
"metadata": {},
"source": [
"### The `alpha` parameter in `geom_imshow()`"
]
},
{
"cell_type": "code",
"execution_count": 1,
"metadata": {
"execution": {
"iopub.execute_input": "2025-11-05T13:48:30.327226Z",
"iopub.status.busy": "2025-11-05T13:48:30.327133Z",
"iopub.status.idle": "2025-11-05T13:48:30.330425Z",
"shell.execute_reply": "2025-11-05T13:48:30.330239Z"
}
},
"outputs": [],
"source": [
"import numpy as np\n",
"\n",
"from lets_plot import *"
]
},
{
"cell_type": "code",
"execution_count": 2,
"metadata": {
"execution": {
"iopub.execute_input": "2025-11-05T13:48:30.331464Z",
"iopub.status.busy": "2025-11-05T13:48:30.331396Z",
"iopub.status.idle": "2025-11-05T13:48:30.333085Z",
"shell.execute_reply": "2025-11-05T13:48:30.332914Z"
}
},
"outputs": [
{
"data": {
"text/html": [
"\n",
" \n",
" \n",
" "
]
},
"metadata": {},
"output_type": "display_data"
}
],
"source": [
"LetsPlot.setup_html()"
]
},
{
"cell_type": "code",
"execution_count": 3,
"metadata": {
"execution": {
"iopub.execute_input": "2025-11-05T13:48:30.346409Z",
"iopub.status.busy": "2025-11-05T13:48:30.346310Z",
"iopub.status.idle": "2025-11-05T13:48:30.660077Z",
"shell.execute_reply": "2025-11-05T13:48:30.659610Z"
}
},
"outputs": [
{
"data": {
"text/plain": [
"(225, 225, 3)"
]
},
"execution_count": 3,
"metadata": {},
"output_type": "execute_result"
}
],
"source": [
"# Load an image\n",
"\n",
"from PIL import Image\n",
"import requests\n",
"from io import BytesIO\n",
"\n",
"response = requests.get('https://github.com/JetBrains/lets-plot-docs/raw/master/source/examples/cookbook/images/fisher_boat.png')\n",
"\n",
"image = Image.open(BytesIO(response.content))\n",
"im_arr = np.asarray(image)\n",
"im_arr.shape"
]
},
{
"cell_type": "code",
"execution_count": 4,
"metadata": {
"execution": {
"iopub.execute_input": "2025-11-05T13:48:30.661330Z",
"iopub.status.busy": "2025-11-05T13:48:30.661208Z",
"iopub.status.idle": "2025-11-05T13:48:30.717611Z",
"shell.execute_reply": "2025-11-05T13:48:30.717379Z"
}
},
"outputs": [
{
"data": {
"text/html": [
" \n",
" "
],
"text/plain": [
""
]
},
"execution_count": 4,
"metadata": {},
"output_type": "execute_result"
}
],
"source": [
"p = ggplot() + geom_point(x=112, y=112, color=\"dark-blue\", size=100, shape=15) + ggsize(450, 450)\n",
"p + ggtitle(\"The background blue square\") + ggsize(400, 300)"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"#### 1. `alpha` parameter and color image"
]
},
{
"cell_type": "code",
"execution_count": 5,
"metadata": {
"execution": {
"iopub.execute_input": "2025-11-05T13:48:30.718607Z",
"iopub.status.busy": "2025-11-05T13:48:30.718528Z",
"iopub.status.idle": "2025-11-05T13:48:30.747966Z",
"shell.execute_reply": "2025-11-05T13:48:30.747773Z"
}
},
"outputs": [
{
"data": {
"text/html": [
" \n",
" "
],
"text/plain": [
""
]
},
"execution_count": 5,
"metadata": {},
"output_type": "execute_result"
}
],
"source": [
"gggrid([\n",
" p + geom_imshow(im_arr) + ggtitle(\"no alpha (opaque image)\"),\n",
" p + geom_imshow(im_arr, alpha=0.7) + ggtitle(\"alpha=0.7\")\n",
"]) + ggsize(1000, 500)"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"#### 2. `alpha` parameter and grayscale image"
]
},
{
"cell_type": "code",
"execution_count": 6,
"metadata": {
"execution": {
"iopub.execute_input": "2025-11-05T13:48:30.749015Z",
"iopub.status.busy": "2025-11-05T13:48:30.748903Z",
"iopub.status.idle": "2025-11-05T13:48:30.750890Z",
"shell.execute_reply": "2025-11-05T13:48:30.750691Z"
}
},
"outputs": [
{
"data": {
"text/plain": [
"(225, 225)"
]
},
"execution_count": 6,
"metadata": {},
"output_type": "execute_result"
}
],
"source": [
"im_arr_gs = im_arr[:,:,0]\n",
"im_arr_gs.shape"
]
},
{
"cell_type": "code",
"execution_count": 7,
"metadata": {
"execution": {
"iopub.execute_input": "2025-11-05T13:48:30.752008Z",
"iopub.status.busy": "2025-11-05T13:48:30.751937Z",
"iopub.status.idle": "2025-11-05T13:48:30.770936Z",
"shell.execute_reply": "2025-11-05T13:48:30.770736Z"
}
},
"outputs": [
{
"data": {
"text/html": [
" \n",
" "
],
"text/plain": [
""
]
},
"execution_count": 7,
"metadata": {},
"output_type": "execute_result"
}
],
"source": [
"gggrid([\n",
" p + geom_imshow(im_arr_gs) + ggtitle(\"no alpha (opaque image)\"),\n",
" p + geom_imshow(im_arr_gs, alpha=0.7) + ggtitle(\"alpha=0.7\"),\n",
"]) + ggsize(1000, 500)"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"#### 3. `alpha` parameter and pseudo-color image"
]
},
{
"cell_type": "code",
"execution_count": 8,
"metadata": {
"execution": {
"iopub.execute_input": "2025-11-05T13:48:30.772172Z",
"iopub.status.busy": "2025-11-05T13:48:30.772098Z",
"iopub.status.idle": "2025-11-05T13:48:30.792966Z",
"shell.execute_reply": "2025-11-05T13:48:30.792694Z"
}
},
"outputs": [
{
"data": {
"text/html": [
" \n",
" "
],
"text/plain": [
""
]
},
"execution_count": 8,
"metadata": {},
"output_type": "execute_result"
}
],
"source": [
"gggrid([\n",
" p + geom_imshow(im_arr_gs, \"magma\") + ggtitle(\"no alpha (opaque image)\"),\n",
" p + geom_imshow(im_arr_gs, \"magma\", alpha=0.7) + ggtitle(\"alpha=0.7\"),\n",
"]) + ggsize(1000, 500)"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"#### 4. `alpha` parameter and grayscale image with transparent pixels (`NaN` values)"
]
},
{
"cell_type": "code",
"execution_count": 9,
"metadata": {
"execution": {
"iopub.execute_input": "2025-11-05T13:48:30.793959Z",
"iopub.status.busy": "2025-11-05T13:48:30.793884Z",
"iopub.status.idle": "2025-11-05T13:48:30.795388Z",
"shell.execute_reply": "2025-11-05T13:48:30.795214Z"
}
},
"outputs": [],
"source": [
"im_arr_gs_nan=im_arr_gs.copy()\n",
"im_arr_gs_nan=im_arr_gs_nan.astype(np.float64)\n",
"im_arr_gs_nan[im_arr_gs_nan < 80] = np.nan"
]
},
{
"cell_type": "code",
"execution_count": 10,
"metadata": {
"execution": {
"iopub.execute_input": "2025-11-05T13:48:30.795997Z",
"iopub.status.busy": "2025-11-05T13:48:30.795923Z",
"iopub.status.idle": "2025-11-05T13:48:30.812045Z",
"shell.execute_reply": "2025-11-05T13:48:30.811857Z"
}
},
"outputs": [
{
"data": {
"text/html": [
" \n",
" "
],
"text/plain": [
""
]
},
"execution_count": 10,
"metadata": {},
"output_type": "execute_result"
}
],
"source": [
"gggrid([\n",
" p + geom_imshow(im_arr_gs_nan, \"magma\", norm=False) + ggtitle(\"no alpha (opaque image)\"),\n",
" p + geom_imshow(im_arr_gs_nan, \"magma\", norm=False, alpha=0.7) + ggtitle(\"alpha=0.7\"),\n",
"]) + ggsize(1000, 500)"
]
}
],
"metadata": {
"kernelspec": {
"display_name": "Python 3 (ipykernel)",
"language": "python",
"name": "python3"
},
"language_info": {
"codemirror_mode": {
"name": "ipython",
"version": 3
},
"file_extension": ".py",
"mimetype": "text/x-python",
"name": "python",
"nbconvert_exporter": "python",
"pygments_lexer": "ipython3",
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