Loading, saving, image types, and file formats

This page explains the difference between the library’s in-memory image types and the disk formats used to load and save them.

That distinction matters because:

image_t describes how pixels are stored while you work on them in memory.
JPEG, PNG, BMP, and TIFF describe how pixels are stored on disk.

In-memory image types

Low-bit monochrome outputs

image_mono1
image_mono2
image_mono4

These are primarily printer-style destination formats for dithering output.

Full monochrome

image_mono stores one greyscale channel per pixel and can be 8-bit or 16-bit when created in memory.

RGB and BGR

image_rgb
image_bgr

These store the same kind of colour data but in different channel order.

RGBA and BGRA

image_rgba
image_bgra

These add alpha for transparency and are ideal for compositing.

CMYK

image_cmyk stores four subtractive channels and is natural for print workflows.

Lab

image_lab stores CIE Lab* colour, which is useful for colour management and interchange.

Bit depth

When you create an image in memory you can choose 8-bit or 16-bit channels for the main full-colour formats.

Higher bit depth gives you more precision and smoother gradients, but it costs more memory, bandwidth, and processing time.

Supported file formats

TIFF

TIFF is the most capable format in this library. It supports monochrome, RGB, RGBA, CMYK, and Lab output; embedded ICC profiles; and both 8-bit and 16-bit channel data.

PNG

PNG is good for lossless RGB-oriented assets and transparent overlays. In this library, 16-bit PNG input is reduced to 8-bit on load, and CMYK/Lab save paths are not supported.

JPEG

JPEG is a compact photographic exchange format. It is useful for distribution but not ideal as a repeatedly edited master format.

BMP

BMP is the simplest supported format. It is useful for debugging and Windows interoperability, but it is not the strongest choice for serious interchange.

Embedded ICC profiles

Where the file format supports it, the library imports embedded ICC profiles on load and can write profile data on save.

Resolution metadata

Images also carry DPI metadata. This does not change the pixels; it tells downstream systems how large those pixels are intended to be physically.

Choosing a format

Choose TIFF when you need CMYK, Lab, 16-bit precision, or robust production storage.

Choose PNG when you need alpha transparency and the asset is RGB-oriented.

Choose JPEG when the source is photographic and file size matters more than exact pixel preservation.

Choose BMP when you need a simple compatibility or debugging format.