Scale Bar

compute_scale_bar

compute_scale_bar

compute_scale_bar(um_per_pixel: float | None, screen_pixels_per_image_pixel: float, *, target_screen_px: float = 120.0, min_screen_px: float = 70.0, max_screen_px: float = 180.0) -> ScaleBarSpec | None

Choose a human-friendly scale bar size for the current zoom.

Parameters:

Name	Type	Description	Default
um_per_pixel	float | None	Physical pixel size in µm. Returns None if unavailable.	required
screen_pixels_per_image_pixel	float	Current zoom factor (screen pixels per image pixel).	required
target_screen_px	float	Desired on-screen length of the bar in pixels.	120.0
min_screen_px	float	Acceptable range of on-screen bar lengths.	70.0
max_screen_px	float	Acceptable range of on-screen bar lengths.	70.0

Returns:

Type	Description
ScaleBarSpec | None	Scale bar specification, or None if pixel size is unknown.

ScaleBarSpec

ScaleBarSpec dataclass

ScaleBarSpec(image_pixels: float, screen_pixels: float, label: str, physical_um: float)

Description of a scale bar to draw on screen.