Table of Contents

PBM / PGM / PPM

In ImageSharp, PbmFormat covers the Netpbm PNM family: PBM for black-and-white images, PGM for grayscale images, and PPM for RGB images. These formats are intentionally simple and are often used for straightforward interchange or tooling pipelines.

ImageSharp exposes PNM-specific APIs through PbmEncoder and PbmMetadata.

Format Characteristics

The PNM family is best thought of as a simple interchange family rather than a compact delivery format.

The family covers three related subformats. PBM stores black-and-white images. PGM stores grayscale images. PPM stores RGB images. Each can be useful for tests, examples, and simple tooling because the structure is easy to generate and inspect.

Plain-text encoding is human-readable, which can be valuable for debugging small fixtures. Binary encoding is more compact and more appropriate for larger files, but it is still not a modern compressed delivery format. The formats do not carry alpha transparency or rich metadata.

A few practical implications:

  • PbmColorType.BlackAndWhite maps to PBM output.
  • PbmColorType.Grayscale maps to PGM output.
  • PbmColorType.Rgb maps to PPM output.
  • PbmEncoding lets you choose plain-text or binary pixel encoding.
  • PbmComponentType lets you choose 1-bit black-and-white, 8-bit components, or 16-bit components depending on the target subformat.

Save as PBM / PGM / PPM

Use PbmEncoder when you want to choose the exact PNM subformat and encoding style:

using SixLabors.ImageSharp;
using SixLabors.ImageSharp.Formats.Pbm;

using Image image = Image.Load("input.png");

image.Save("output.ppm", new PbmEncoder
{
    ColorType = PbmColorType.Rgb,
    ComponentType = PbmComponentType.Byte,
    Encoding = PbmEncoding.Binary
});

Key PNM Encoder Options

The most commonly used PbmEncoder options are:

  • ColorType selects PBM, PGM, or PPM style output.
  • ComponentType selects 1-bit, 8-bit, or 16-bit component storage where that subformat allows it.
  • Encoding selects plain-text or binary pixel encoding.

Choose the subformat from the data model. A mask or thresholded image belongs in PBM, grayscale analysis output belongs in PGM, and ordinary RGB test data belongs in PPM. Choose plain text when inspection matters more than size.

Read PNM Metadata

Use GetPbmMetadata() to inspect PNM-specific metadata:

using SixLabors.ImageSharp;
using SixLabors.ImageSharp.Formats.Pbm;

using Image image = Image.Load("input.ppm");

PbmMetadata pbmMetadata = image.Metadata.GetPbmMetadata();

Console.WriteLine(pbmMetadata.ColorType);
Console.WriteLine(pbmMetadata.ComponentType);
Console.WriteLine(pbmMetadata.Encoding);

PbmMetadata includes values such as:

  • ColorType
  • ComponentType
  • Encoding

When to Use PBM / PGM / PPM

The Netpbm family is usually worth considering when:

  • You need a very simple interchange format.
  • Human-readable plain-text image data is useful for debugging or tooling.
  • You are working with existing Netpbm-style workflows.

It is usually a poor fit when:

  • File size matters.
  • You need richer metadata, transparency, or modern delivery characteristics.

For more compact or full-featured output, start with PNG, WebP, or QOI.

Practical Guidance

  • Use Netpbm formats for simple tooling, tests, and interchange workflows where readability matters.
  • Avoid them for public delivery or storage where compression, metadata, or alpha support matters.
  • Be explicit about plain versus binary encoding when files are consumed by external tools.
  • Prefer PNG when you need a simple lossless format with a much broader ecosystem.
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