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{
"cell_type": "markdown",
"id": "50d58bcd",
"metadata": {},
"source": [
"# trans_graph\n",
"Demonstrates how to access and manipulate ARGB pixel values of an image +...\n",
" - how to make a part of an image to be transparent.\n",
" - how to merge/alphablend an image with transparent colors\n",
" with some background image.\n",
"\n",
"\n",
"\n",
"\n",
"**Author:** Valeriy Onuchin \n",
"This notebook tutorial was automatically generated with ROOTBOOK-izer from the macro found in the ROOT repository on Tuesday, May 19, 2026 at 08:38 PM."
]
},
{
"cell_type": "markdown",
"id": "611715e4",
"metadata": {},
"source": [
" Definition of a helper function: "
]
},
{
"cell_type": "code",
"execution_count": 1,
"id": "977de68d",
"metadata": {
"collapsed": false,
"execution": {
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"source": [
"%%cpp -d\n",
"\n",
"#include \"TColor.h\"\n",
"#include \"TImage.h\"\n",
"#include \"TImageDump.h\"\n",
"#include \"TVirtualPad.h\"\n",
"#include \"TROOT.h\"\n",
"#include \"TFrame.h\"\n",
"\n",
"UInt_t color2rgb(TColor *col)\n",
"{\n",
" // returns RGB value of color\n",
"\n",
" return ((UInt_t(col->GetRed() * 255) << 16) + (UInt_t(col->GetGreen() * 255) << 8) + UInt_t(col->GetBlue() * 255));\n",
"}"
]
},
{
"cell_type": "markdown",
"id": "0565a751",
"metadata": {},
"source": [
"remember if we are in batch mode"
]
},
{
"cell_type": "code",
"execution_count": 2,
"id": "22a6f27a",
"metadata": {
"collapsed": false,
"execution": {
"iopub.execute_input": "2026-05-19T20:38:47.300282Z",
"iopub.status.busy": "2026-05-19T20:38:47.300165Z",
"iopub.status.idle": "2026-05-19T20:38:47.630279Z",
"shell.execute_reply": "2026-05-19T20:38:47.629576Z"
}
},
"outputs": [],
"source": [
"Bool_t batch = gROOT->IsBatch();"
]
},
{
"cell_type": "markdown",
"id": "7b32f87a",
"metadata": {},
"source": [
"switch to batch mode"
]
},
{
"cell_type": "code",
"execution_count": 3,
"id": "92f6c394",
"metadata": {
"collapsed": false,
"execution": {
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"shell.execute_reply": "2026-05-19T20:38:47.843159Z"
}
},
"outputs": [],
"source": [
"gROOT->SetBatch(kTRUE);"
]
},
{
"cell_type": "markdown",
"id": "2370deb2",
"metadata": {},
"source": [
"execute gr001_simple.C macro"
]
},
{
"cell_type": "code",
"execution_count": 4,
"id": "ba8181b6",
"metadata": {
"collapsed": false,
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"shell.execute_reply": "2026-05-19T20:38:48.047850Z"
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"outputs": [
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"text": [
" i 0 0.000000 1.986693 \n",
" i 1 0.100000 2.955202 \n",
" i 2 0.200000 3.894183 \n",
" i 3 0.300000 4.794255 \n",
" i 4 0.400000 5.646425 \n",
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" i 6 0.600000 7.173561 \n",
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" i 9 0.900000 8.912074 \n",
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" i 11 1.100000 9.635582 \n",
" i 12 1.200000 9.854497 \n",
" i 13 1.300000 9.974950 \n",
" i 14 1.400000 9.995736 \n",
" i 15 1.500000 9.916648 \n",
" i 16 1.600000 9.738476 \n",
" i 17 1.700000 9.463001 \n",
" i 18 1.800000 9.092974 \n",
" i 19 1.900000 8.632094 \n",
" i 0 -3.000000 -0.989992 \n",
" i 1 -2.684211 -0.897212 \n",
" i 2 -2.368421 -0.715699 \n",
" i 3 -2.052632 -0.463406 \n",
" i 4 -1.736842 -0.165284 \n",
" i 5 -1.421053 0.149185 \n",
" i 6 -1.105263 0.448899 \n",
" i 7 -0.789474 0.704219 \n",
" i 8 -0.473684 0.889894 \n",
" i 9 -0.157895 0.987561 \n",
" i 10 0.157895 0.987561 \n",
" i 11 0.473684 0.889894 \n",
" i 12 0.789474 0.704219 \n",
" i 13 1.105263 0.448899 \n",
" i 14 1.421053 0.149185 \n",
" i 15 1.736842 -0.165284 \n",
" i 16 2.052632 -0.463406 \n",
" i 17 2.368421 -0.715699 \n",
" i 18 2.684211 -0.897212 \n",
" i 19 3.000000 -0.989992 \n"
]
}
],
"source": [
"gROOT->Macro(\"$ROOTSYS/tutorials/visualisation/graphs/gr001_simple.C\");"
]
},
{
"cell_type": "markdown",
"id": "369b3e99",
"metadata": {},
"source": [
"create gVirtualPS object"
]
},
{
"cell_type": "code",
"execution_count": 5,
"id": "6c728b36",
"metadata": {
"collapsed": false,
"execution": {
"iopub.execute_input": "2026-05-19T20:38:48.049632Z",
"iopub.status.busy": "2026-05-19T20:38:48.049499Z",
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"shell.execute_reply": "2026-05-19T20:38:48.256566Z"
}
},
"outputs": [],
"source": [
"TImageDump dmp(\"dummy.png\");\n",
"TImage *fore = dmp.GetImage(); // image associated with image_dump"
]
},
{
"cell_type": "markdown",
"id": "3c849cda",
"metadata": {},
"source": [
"resize canvas"
]
},
{
"cell_type": "code",
"execution_count": 6,
"id": "63d4a835",
"metadata": {
"collapsed": false,
"execution": {
"iopub.execute_input": "2026-05-19T20:38:48.258643Z",
"iopub.status.busy": "2026-05-19T20:38:48.258513Z",
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"shell.execute_reply": "2026-05-19T20:38:48.465545Z"
}
},
"outputs": [],
"source": [
"gPad->SetCanvasSize(400, 300);\n",
"gPad->Paint(); // paint gPad on fore image associated with TImageDump"
]
},
{
"cell_type": "markdown",
"id": "97bab7f0",
"metadata": {},
"source": [
"open background image"
]
},
{
"cell_type": "code",
"execution_count": 7,
"id": "b4c7d124",
"metadata": {
"collapsed": false,
"execution": {
"iopub.execute_input": "2026-05-19T20:38:48.468028Z",
"iopub.status.busy": "2026-05-19T20:38:48.467906Z",
"iopub.status.idle": "2026-05-19T20:38:48.670345Z",
"shell.execute_reply": "2026-05-19T20:38:48.669668Z"
}
},
"outputs": [],
"source": [
"TImage *back = TImage::Open(\"$ROOTSYS/tutorials/visualisation/image/rose512.jpg\");"
]
},
{
"cell_type": "markdown",
"id": "6e4c5cfc",
"metadata": {},
"source": [
"choose colors to be transparent"
]
},
{
"cell_type": "code",
"execution_count": 8,
"id": "f927bdcf",
"metadata": {
"collapsed": false,
"execution": {
"iopub.execute_input": "2026-05-19T20:38:48.672415Z",
"iopub.status.busy": "2026-05-19T20:38:48.672293Z",
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"shell.execute_reply": "2026-05-19T20:38:48.883890Z"
}
},
"outputs": [],
"source": [
"TColor *bk1 = gROOT->GetColor(gPad->GetFillColor());\n",
"TColor *bk2 = gROOT->GetColor(gPad->GetFrame()->GetFillColor());\n",
"UInt_t rgb1 = color2rgb(bk1);\n",
"UInt_t rgb2 = color2rgb(bk2);"
]
},
{
"cell_type": "markdown",
"id": "9fa52be2",
"metadata": {},
"source": [
"get directly accessible ARGB array"
]
},
{
"cell_type": "code",
"execution_count": 9,
"id": "78f79ded",
"metadata": {
"collapsed": false,
"execution": {
"iopub.execute_input": "2026-05-19T20:38:48.886296Z",
"iopub.status.busy": "2026-05-19T20:38:48.886173Z",
"iopub.status.idle": "2026-05-19T20:38:49.098532Z",
"shell.execute_reply": "2026-05-19T20:38:49.097799Z"
}
},
"outputs": [],
"source": [
"UInt_t *argb = fore->GetArgbArray();\n",
"UInt_t w = fore->GetWidth();\n",
"UInt_t h = fore->GetHeight();"
]
},
{
"cell_type": "markdown",
"id": "0165ffb8",
"metadata": {},
"source": [
"scan all pixels in fore image and\n",
"make rgb1, rgb2 colors transparent."
]
},
{
"cell_type": "code",
"execution_count": 10,
"id": "50f92eb4",
"metadata": {
"collapsed": false,
"execution": {
"iopub.execute_input": "2026-05-19T20:38:49.100566Z",
"iopub.status.busy": "2026-05-19T20:38:49.100444Z",
"iopub.status.idle": "2026-05-19T20:38:49.302767Z",
"shell.execute_reply": "2026-05-19T20:38:49.302089Z"
}
},
"outputs": [],
"source": [
"for (UInt_t i = 0; i < h; i++) {\n",
" for (UInt_t j = 0; j < w; j++) {\n",
" Int_t idx = i * w + j;\n",
"\n",
" // RGB part of ARGB color\n",
" UInt_t col = argb[idx] & 0xffffff;\n",
"\n",
" // 24..31 bits define transparency of the color in the range 0 - 0xff\n",
" // for example, 0x00000000 - black color with 100% transparency\n",
" // 0xff000000 - non-transparent black color\n",
"\n",
" if ((col == rgb1) || (col == rgb2)) { //\n",
" argb[idx] = 0; // 100% transparent\n",
" } else {\n",
" argb[idx] = 0xff000000 + col; // make other pixels non-transparent\n",
" }\n",
" }\n",
"}"
]
},
{
"cell_type": "markdown",
"id": "a2f6e573",
"metadata": {},
"source": [
"alphablend back and fore images"
]
},
{
"cell_type": "code",
"execution_count": 11,
"id": "f9c2a9b1",
"metadata": {
"collapsed": false,
"execution": {
"iopub.execute_input": "2026-05-19T20:38:49.304784Z",
"iopub.status.busy": "2026-05-19T20:38:49.304652Z",
"iopub.status.idle": "2026-05-19T20:38:49.517056Z",
"shell.execute_reply": "2026-05-19T20:38:49.516368Z"
}
},
"outputs": [],
"source": [
"back->Merge(fore, \"alphablend\", 20, 20);"
]
},
{
"cell_type": "markdown",
"id": "57e58003",
"metadata": {},
"source": [
"write result image in PNG format"
]
},
{
"cell_type": "code",
"execution_count": 12,
"id": "637b3b74",
"metadata": {
"collapsed": false,
"execution": {
"iopub.execute_input": "2026-05-19T20:38:49.519109Z",
"iopub.status.busy": "2026-05-19T20:38:49.518974Z",
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"shell.execute_reply": "2026-05-19T20:38:49.730870Z"
}
},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"*************** File trans_graph.png created ***************\n"
]
}
],
"source": [
"back->WriteImage(\"trans_graph.png\");\n",
"printf(\"*************** File trans_graph.png created ***************\\n\");\n",
"\n",
"delete back;"
]
},
{
"cell_type": "markdown",
"id": "f8296a1b",
"metadata": {},
"source": [
"switch back to GUI mode"
]
},
{
"cell_type": "code",
"execution_count": 13,
"id": "befe08db",
"metadata": {
"collapsed": false,
"execution": {
"iopub.execute_input": "2026-05-19T20:38:49.733092Z",
"iopub.status.busy": "2026-05-19T20:38:49.732967Z",
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"shell.execute_reply": "2026-05-19T20:38:49.944619Z"
}
},
"outputs": [],
"source": [
"if (!batch)\n",
" gROOT->SetBatch(kFALSE);"
]
},
{
"cell_type": "markdown",
"id": "8f14ae90",
"metadata": {},
"source": [
"Draw all canvases "
]
},
{
"cell_type": "code",
"execution_count": 14,
"id": "3efa83a7",
"metadata": {
"collapsed": false,
"execution": {
"iopub.execute_input": "2026-05-19T20:38:49.946935Z",
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"shell.execute_reply": "2026-05-19T20:38:50.158317Z"
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"source": [
"gROOT->GetListOfCanvases()->Draw()"
]
}
],
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