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Issue of the Implementation # S0641

Brief

Images change when scaled 1:1 with GDK_INTERP_HYPER filter

Detailed Description

The GDK_INTERP_HYPER filter is described as follows in the documentation for gdk-pixbuf scaling functions:

This is the slowest and highest quality reconstruction function. It is derived from the hyperbolic filters in Wolberg's "Digital Image Warping", and is formally defined as the hyperbolic-filter sampling the ideal hyperbolic-filter interpolated image (the filter is designed to be idempotent for 1:1 pixel mapping).

It appears from the note in the brackets that if an image is scaled 1:1 with this filter applied, the image should remain the same.

The attached example code using gdk_pixbuf_scale_simple shows that this is not the case. This problem affects other scaling functions too:

• gdk_pixbuf_scale
• gdk_pixbuf_composite
• gdk_pixbuf_composite_color
• gdk_pixbuf_composite_color_simple

Problem location(s) in the standard

Gdk-pixbuf 2.6.2 API Reference, Scaling

Component

gtk-gdk-pixbuf 2.6.2 or later

Accepted

Gnome Bugzilla 496306

Status

Fixed in gtk-gdk-pixbuf 2.31

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