HDR to PNM API
POST a .hdr to /v2/convert/hdr/to/pnm and get a binary PPM with the magic number P6 and a maxval of 255. The shared-exponent pixels are decoded, clipped at 1.0 and stored as three plain bytes each, row by row from the top.
- Endpoint
- POST /v2/
convert/ hdr/ to/ pnm - Accepts
- hdr
- Sample timing
- 22 ms median of 5 runsHow we measure
- Request size
- Up to 10 MB on the Free plan or 100 MB on paid plans, all files together
Request and response
Every sample below ran against the API before this page was published. Set PDFCONVERSIONAPI_KEY to your key and run it as is.
curl -sS -X POST \
https://api.pdfconversionapi.com/v2/convert/hdr/to/pnm \
-H "Authorization: Bearer $PDFCONVERSIONAPI_KEY" \
-F File=@lakeside-sunset-sky.hdr \
-o response.json
# FileData is base64. Save the first file in converted/,
# or print the JSON error.
if jq -e '.Files' response.json > /dev/null; then
mkdir -p converted
name=$(jq -r '.Files[0].FileName' response.json)
jq -r '.Files[0].FileData' response.json \
| base64 --decode > "converted/$name"
else
cat response.json
fiimport base64
import os
import requests
key = os.environ["PDFCONVERSIONAPI_KEY"]
response = requests.post(
"https://api.pdfconversionapi.com/v2/convert/hdr/to/pnm",
headers={"Authorization": f"Bearer {key}"},
files=[("File", open("lakeside-sunset-sky.hdr", "rb"))],
timeout=180,
)
result = response.json()
if not response.ok:
raise SystemExit(f"{result['Code']}: {result['Message']}")
os.makedirs("converted", exist_ok=True)
for file in result["Files"]:
path = os.path.join("converted", file["FileName"])
with open(path, "wb") as out:
out.write(base64.b64decode(file["FileData"]))
print(path, file["FileSize"], "bytes")
import { mkdir, readFile, writeFile } from "node:fs/promises";
import { join } from "node:path";
const form = new FormData();
const file = "lakeside-sunset-sky.hdr";
form.append("File", new Blob([await readFile(file)]), file);
const url = "https://api.pdfconversionapi.com/v2/convert/hdr/to/pnm";
const key = process.env.PDFCONVERSIONAPI_KEY;
const response = await fetch(url, {
method: "POST",
headers: { Authorization: `Bearer ${key}` },
body: form,
});
const result = await response.json();
if (!response.ok) {
throw new Error(`${result.Code}: ${result.Message}`);
}
await mkdir("converted", { recursive: true });
for (const file of result.Files) {
const path = join("converted", file.FileName);
await writeFile(path, Buffer.from(file.FileData, "base64"));
console.log(path, file.FileSize, "bytes");
}
{
"ConversionCost": 1,
"ConversionTime": 0.022,
"Files": [
{
"FileName": "lakeside-sunset-sky.pnm",
"FileExt": "pnm",
"FileSize": 240015,
"FileData": "UDYKNDAwIDIwMCAyNTUKECFh…"
}
]
}Response from our test run on 2026-11-03. ConversionTime shows the median of 5 runs. FileData is shortened here; the real response carries the whole file as base64.
The sample, converted
The same file the code sends. Download the input and the output and compare them yourself.

- Input
- lakeside-sunset-sky.hdr (90 KB)
- Output
- lakeside-sunset-sky.pnm (234 KB)
- Source
- A sunset sky panorama we drew in code and saved as a 400 × 200 Radiance RGBE file with run-length scanlines; the sun disc is 60.0. (CC0-1.0). How it was made
- Made by
- 2026-11-04, API build
9eeeb0640aba
Parameters
Send these as form fields next to the file. Names are case-insensitive. If you set one of the documented options below that we don't support yet, the request fails with a 400 that names it instead of returning a file made without it.
| Parameter | What it does |
|---|---|
ImageWidthinteger | Target width. ImageWidth=120 gave a 120 60 255 header and 21,614 bytes.Values: 1–20000 |
ImageHeightinteger | Target height; ImageHeight=100 gave 200 × 100 in 60,015 bytes.Values: 1–20000 |
ScaleProportionsboolean, default true | false makes a 200 × 200 box exact, 120,015 bytes. |
ScaleIfLargerboolean, default false | true turns off upscaling, which otherwise writes 960,015 bytes for ImageWidth=800. |
ScaleImageboolean, default true | false crops a corner of the requested size instead of scaling. |
ColorSpaceenum, default default | gray and monochrome switch to a one-channel P5 file of 80,015 bytes; monochrome holds only 0 and 255.Values: default, rgb, gray, monochrome; cmyk returns 400 |
FileNamestring | Stem of the .pnm file name. |
StoreFileboolean, default false | Link valid for 3 hours instead of inline bytes. |
What carries over, and what doesn't
Kept
- The image in reading order: 400 × 200 RGB triplets right after the 15-byte header
- Values from 0 to 1 rounded to 8 bits: the zenith pixel is (16, 33, 97)
- A fully opaque picture, as in the source
Lost or not yet supported
- The shared exponent and all range above 1.0; the sun and the middle of its reflection are (255, 255, 255).
- 16-bit depth: the maxval is 255.
- Size: 240,015 bytes, 2.6 times the run-length coded .hdr.
Limits
- One .hdr per conversion.
- Total request size 10 MB on the Free plan or 100 MB on paid plans.
- Up to 100,000,000 pixels.
-Y … +X …orientation only.- Stops after 120 seconds.
Where teams use it
Datasets for vision research
Code that trains or tests on sky and lighting images can read raw RGB behind a text header. A PPM copy of each .hdr loads with a few lines of code.
Command-line pipelines
Netpbm-style tools chain on raw pixel files. Converting the Radiance image once lets the rest of a shell pipeline work without RGBE support.
Questions
What does the header look like?
Two short lines: P6, then 400 200 255 for width, height and maxval. The 240,000 pixel bytes follow directly.
Does AlphaColor do anything here?
No. PNM output is flattened onto AlphaColor, but a Radiance file has no transparent pixels, so the result is byte-identical with or without it.
Can I keep values above 1.0?
No. PPM stores integers up to its maxval, and this route clips the decoded light to 1.0 before writing 255. Keep the .hdr for the full range.
Convert your first HDR file in a minute.