Severe Moiré Pattern / Aliasing Artifacts When Downscaling High-Frequency Images

[vzsoft]

Hi,

When displaying an image files, and I've encountered a significant visual issue when resizing images that contain high-frequency, repeating patterns (like a fingerprint or fine-lined textures).

Problem Description
When the image is rendered at a smaller size than its original resolution (downscaling), it produces severe Moiré patterns and aliasing artifacts. The fine lines of the original image merge into large, distracting, wavy bands, completely distorting the image.

This appears to be a classic texture minification problem.

Visual Example
Expected Behavior (Original Image at 1:1 or properly filtered): The image should show clear, distinct lines. (

)

Actual Behavior (Downscaled Image): The image shows strong Moiré patterns and artifacts. (

)

Possible Cause
This strongly suggests that Mipmaps are either not being generated for the image texture, or the texture sampler is not using an appropriate filter (like Trilinear or Anisotropic) when downscaling. The sampler seems to be using a simple Bilinear or Nearest Neighbor filter, which is insufficient for high-frequency textures and causes this aliasing.

Thank you for looking into this.

[vzsoft]

Orginal Image File

[SuRGeoNix]

This is the same as #342
However, further testing (especially with the new upcoming renderer that will support d3d11 also for software decoded frames) shows that in order d3d11 scaler will work properly should feed it with NV12 format. This adds extra convert of RGBA in this case to NV12. I would like to confirm this if you could provide an NV12 format of it?

Also custom scalers such lanczos will not really improve the quality so adding extra scalers for FlyleafVP still does not make any sense. D3D11 should handle those by feeding it properly.

Another possible failure of proper downscaling is that the width is odd... require more testing to validate those...

This will require a different pixel shader to convert RGB(A) -> NV12 (different coeffs etc.) and probably that's the issue that it needs an NV12 input.

[vzsoft]

Thanks for the quick response.

1. Regarding NV12: You asked for an NV12 version. Do you mean you want me to manually convert the source PNG into a raw NV12 file for you to test? Or are you suggesting I should be doing this conversion in my code before passing the frame to Flyleaf?

2. Regarding Dimensions: I checked the image. The original dimensions are 381x2130 pixels.

3. I did this with 2 other programs and they had no problem (video file)
   https://github.com/user-attachments/assets/b387eb30-be9d-4db5-a9cf-57f93f68b00c

4. Maybe the problem is the odd number!

Since this is a static RGBA image, If this is the required solution, could Flyleaf's renderer handle this internal conversion automatically when it detects an RGBA input?

[SuRGeoNix]

An NV12 format (raw should be fine) would help to quickly test with the new renderer if it still has the issue. But no worries if you can't I will do it just later on.