Preview looks less noisy than the actual image

[njeevanjee]

I am new to narrow band imaging. For a test I took one 3 minute H-Alpha image of Rosette nebula from a light polluted sky using ASI1600MM camera and 1.25 Ha filter. I was amazed with amount of detail I could see.  Using histogram and STF process I did some stretching and applied it to the raw image. Preview looked pretty good but I was surprised to see that actual image look much more noisy than the preview. Is this normal or I am missing something?
Image attached below.

Nasir

[jwaters125]

The Preview was set to 'Smooth'.  Set it to 'Maximum'.  Lower right corner.

[njeevanjee]

I tried setting it to Maximum but it made very little difference. If I zoom into preview it does appear to be as noisy as the actual image but at full view preview definitely looks more clean.

[Juan Conejero]

The real-time preview interface and image windows use very different algorithms to generate screen renditions. The R-T preview aims at producing fast approximations, while image windows are much more accurate. As you have discovered, if you really want to see your data represented accurately, use zoom ratios of 1:2 or higher.

[njeevanjee]

Thanks Juan! Yes I noticed that if I zoom in to preview image then both the images appear quite similar at same zoom level.