Odd horizontal lines in real time preview

[Nocturnal]

Hi,

have a look at the screenshot here:

http://gallery.tungstentech.com/main.php?g2_itemId=1399 (may need to view the 1:1 version)

you'll notice that the white galaxy has faint black horizontal lines. Likely resizing artifacts but I don't remember seeing this before and I use this feature all the time. The lines are also visible when looking at the ACDR preview (ie. luminance mask preview unchecked). I see the same for histogramtransform so this appears to be generic to the RTP window.

Bonus bug: uncheck the RTP icon 'show transformed image' and then resize the RTP window. Poof! The preview shows the modified image again.

[Juan Conejero]

Hi Sander,

You've discovered a change and a bug

Those odd lines come from a change in 1.5: when the real-time preview image is being magnified with respect to the original, the smooth quality option is internally replaced by maximum quality. This is because smooth quality generates inaccurate/useless screen representations when the ratio screen_pixels:image_pixels is greater than one. For example, if you open a small image, say a 16x16 png icon and select it on the Real Time Preview window, you'll see it perfectly represented in PI 1.5, but in PI 1.4.x and older, the representation was terribly bad in smooth mode.

A side effect of this behavior change is the odd lines that occur sometimes. They happen when the real-time preview image is enlarging the original image by a factor slightly greater than one, and are due to small rounding errors. They are only visible sometimes, and not all LCD panels show them with the same intensity. They should disappear if you resize a bit the RT preview.

The other thing is actually a small bug. Yes, the state of the Show transformed image button should be preserved when the window is resized. Thanks for catching it!

[Nocturnal]

Hi Juan,

I'm not convinced, sorry. The lines should not appear with proper interpolation. Frankly I'm surprised you are so accepting of these artifacts I just tried it with quality set to 'maximum' and the same artifacts occur. I think it's related to the vertical scaling. The horizontal scaling is fine.

If the scale is so critical in this version then I think a 1:1 button should be added to the real time preview window or maybe you can tell me how to make it 1:1. I don't want any resizing done if I can avoid it.

[Juan Conejero]

Hi Sander,

Frankly I'm surprised you are so accepting of these artifacts

Aha, you know how to shake me

I have fixed this problem in 1.5.2. I was applying a too simplistic criterion (preview_image:actual_image pixel ratio >= 1) to block smooth bitmap interpolation. Now I have refined it: smoothing is allowed while the *screen* representation of an original pixel spans for less than 2 pixels. This works very well and doesn't hurt representation of small images.

Thanks for shaking

[Nocturnal]

Hi Juan,

I'm glad to have shaken you It's only because I know your standards are very high and I suspected in this case you weren't seeing the forest through the trees