Why Are My MaterialSkin TabSelector Icons Rendered in Low Quality in C# WinForms?

Below is a summary of what’s likely happening and some steps you can take:

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What’s Happening

Even though your image files are “properly sized” (e.g. 32×32) and your ImageList is configured with matching dimensions, once you add an image to an ImageList the control converts it to a bitmap of the configured size. When that bitmap is later drawn by the MaterialSkin TabSelector, it’s already been “pre‐scaled” (or cached) and might not use the full quality of your original file. In other words, the ImageList is essentially downscaling (or reformatting) your image under the hood and locking it into that quality—even when you later set the graphics properties (smoothing, interpolation, etc.) to high quality.

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Steps to Try

1. Double‑check the Actual Image Pixels
   Verify that your icon files are exactly 32×32 (or the size set in the ImageList). Any slight difference (or added padding) can force a rescaling operation.

2. ImageList Caching
   Realize that ImageList always caches images at the time they are added. If your images are added via a designer or code and then later drawn using high‑quality graphics settings, that cached low‑quality bitmap may not get improved by changing the interpolation mode. One workaround is to bypass the ImageList cache and draw directly from your high‑resolution source image if possible.

3. DPI Settings
   Check if the system or application DPI settings are influencing the final drawn size. You might want to ensure your form is set to use the appropriate DPI mode (for example, using

   CSHARPCopied
   Application.SetHighDpiMode(HighDpiMode.SystemAware);

   in .NET Core 3.0+).

4. MaterialSkin Source Code
   The MaterialSkin TabSelector explicitly draws the image into a fixed rectangle with a constant (ICON_SIZE) value. If the image stored in the ImageList is already “baked in” at a particular quality, then even the improved graphics modes (HighQualityBicubic, etc.) will only affect the scaling from that cached bitmap.

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What You Can Do Next

• Use the Original Image: Consider storing and drawing the original icon images rather than using the ImageList’s cached copies. You could manage your own image collection and change the drawing code to use these images in their “native” quality.

• Update the ImageList on Demand: If you must use ImageList, try removing and re‑adding the images after adjusting any DPI or quality settings. This may force ImageList to use your updated images rather than a cached version.

• Custom Draw Override: If modifying MaterialSkin’s code is an option, override the drawing behavior of TabSelector to retrieve and draw the original image or to perform a custom rescaling (e.g. using your own off‑screen high‑quality drawing routine).

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Conclusion

You aren’t “missing” a graphics mode setting as you’ve already attempted to change the smoothing/interpolation settings. The issue is more likely tied to how ImageList handles images internally (as a cached bitmap at a fixed size) and then how that bitmap is drawn by MaterialSkin. To work around the problem, consider bypassing or recreating the cached image so that your draw call uses a high‑quality source.

If you have control over the MaterialSkin source, you might experiment with drawing directly from a high‑quality image rather than from the ImageList’s copy. This change should give you better control over the end result.

Feel free to ask more questions if you need further clarification on any of these points!