Skip to content

Images & DPI

Images in Tk are first-class objects with lifetimes independent of widgets. Understanding how images behave — especially under high-DPI displays — is essential for building correct and visually consistent bootstack applications.

This page explains how Tk handles images, common pitfalls, and how bootstack provides structure around image usage.

Images as objects

In Tk, images are not owned by widgets.

Instead:

  • images are created as named objects in the Tk interpreter
  • widgets reference images by name
  • images persist until explicitly destroyed or garbage-collected

If an image object is garbage-collected in Python, widgets that reference it may stop displaying it.

This behavior is a common source of bugs.

Image lifetime

Because images outlive widgets:

  • the image must be kept alive for as long as it is displayed
  • destroying a widget does not destroy its image
  • losing the last Python reference can invalidate the image

bootstack encourages treating images as application-level resources rather than widget-local objects.

DPI and scaling

Modern systems often use high-DPI displays.

Tk handles DPI scaling by:

  • scaling fonts automatically
  • scaling images only if explicitly configured

This means images that look correct on standard displays may appear blurry or incorrectly sized on high-DPI screens.

bootstack’s approach to images

bootstack introduces conventions and helpers to manage images consistently:

  • centralized image creation and caching
  • explicit DPI-aware sizing
  • reuse of images across widgets

This avoids duplicating image-loading logic and reduces memory usage.

Image caching

Creating images repeatedly is expensive.

Caching images:

  • improves performance
  • ensures consistent appearance
  • simplifies lifetime management

bootstack provides an Image abstraction to manage caching and reuse. See Guides → Icons for using framework-managed icons.

Image formats

Tk natively supports a limited set of image formats.

bootstack encourages using Pillow-backed images when broader format support is required, while still integrating with Tk’s image model.

This allows applications to use modern image assets without sacrificing compatibility.

Common pitfalls

  • creating images inside widget constructors
  • failing to keep a reference to an image
  • ignoring DPI scaling
  • loading the same image repeatedly

Understanding image behavior helps avoid these problems.

Next steps