CapturePreviewCSharp: Image quality is blocky

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  • Posts: 1
  • Joined: Tue Nov 27, 2018 6:12 am
  • Real Name: shinji satoh

CapturePreviewCSharp: Image quality is blocky

PostTue Nov 27, 2018 6:29 am

Hi all,

I am using Decklink Mini Recorder on Windows 10.

I used the sample program CapturePreviewCSharp.
Input from HDMI AppleTV (1280 x 720).
I changed the size of the previewWindow in the CapturePreview form to 1280x720.

but, it is displayed with rough image quality.
Bitmap acquired and saved by GetBytes() from theFrame was not a problem.

Can I use IDeckLinkDX9ScreenPreviewHelper to display on the form with the correct image quality?
Is the sample program working properly in your environment?
GetBytes() -> BMP
ok.jpeg (79.75 KiB) Viewed 91 times
Capture from form with m_previewHelper.Render(rect);
ng.jpeg (88.01 KiB) Viewed 91 times

Cameron Nichols

Blackmagic Design

  • Posts: 132
  • Joined: Mon Sep 04, 2017 4:05 am

Re: CapturePreviewCSharp: Image quality is blocky

PostWed Nov 28, 2018 3:13 am

Hi Shinji,

There are two reasons why you are observing this:
Firstly, the screen preview helpers (eg IDeckLinkDX9ScreenPreviewHelper) are by design for small screen rendering by dropping every second line. We have a FAQ posted on the developer site for developers who want to generate their own full-screen preview helpers. - Full screen preview with DeckLink screen preview helpers

Secondly, you may want to try resizing your preview window to 1 pixel less than the captured frame size (ie 1279 x 719). Because the Direct3D top-left vertices is from (-0.5,-0.5), it will try to render from a frame of size 1281 x 721, then you will see some aliasing due to non-integral upscaling.

There is a good reference on Windows Dev Center on Direct3D rasterization rules: ... tion-rules


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