About Thredgeholder Pro v1.2

Thredgeholder Pro is an advanced edge detection plugin, simple in operation but extremely effective.

Using Thredgeholder Pro

Thredgeholder Pro selectively detects edges for a number of different 'channels' in the image, such as the red component, the degree of saturation, or the 'a' channel in the LAB colour model.

The image on the left shows the interface when the plugin is first run.

At the top of the controls are four buttons for selecting which page of controls you want to change; HSL, RGB, IUV or LAB filtering. Each page sets the parameters for a set of three channels. All sets of controls are active at the same time when filtering; the HSL/RGB/IUV/LAB selection is only for selecting the page of controls you want to change.

For each channel (HSL/RGB/IUV/LAB) there is an activation checkbox. If the checkbox is ticked, that channel is filtered. If not ticked, that channel plays no part in the filter's results. By default only the Luminance channel is enabled on filter startup.

Each channel has two sliders.

  • 'Threshold' determines the degree of sensitivity to edges. Low values will tend to show background noise. By increasing the threshold you can select only the more prominent edges in the image.
  • 'Brightness' specifies the lightness/darkness of the edges. Higher values give a softer image, whereas low values create higher contrast. Setting Brightness to the same value as Threshold gives an absolute threshold of black and white. Brightness cannot be set to a value lower than Threshold, and vice versa.

The following illustrates using Thredgeholder Pro to select the edges in this image...

 

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With only the Red channel active there's strong definition of the glass but the ribbons are less visible

 

 

Deactivating the Red channel and activating filtering on the V channel, the glass definition is virtually lost but the ribbons are clear and strong

 

 

 

By activating both the Red and V channels, we get the best of both worlds with clear glass edging and ribbon definition

 

 

 

Hints for use

Wherever possible, use high quality source images. JPEGs have low-level colour distortion created when the image is compressed. This introduces a lot of noise to sensitive edge detection, especially in the Hue channel, which appear as rectangular areas of edges.

The preview image shows a scaled down version of the Source data. The settings are applied to this downscaled image during the preview. For an accurate preview of the filter when applied, set the preview zoom to 100%.

The 'Luminance', 'i' and 'L' channels produce similar results, but with different areas of sensitivity. eg. The 'L' channel is effective at finding detail in areas of shadow.