How to smooth image after blurring?

[snibgo]

With Q16 IM, without "+depth", stair-stepping between areas is inevitable, as the output is 8 bits/channel/pixel and there are only 38 different tones.

With Q16 or better, with "+depth", we have more than 9000 tones, and I can't see any problem. Perhaps I don't understand the issue.

Using "-gaussian-blur" instead of "-blur" makes a slight difference, further reducing the number of adjacent pixels that are equal, and spreading them more evenly throughout the image.

Test script (Windows BAT syntax):

Code: Select all

%IM%convert ^
  before_blur.jpg -blur 0x50 ^
  +depth ^
  sm_blur2.png

%IM%convert ^
  sm_blur2.png ^
  -unique-colors info:

%IM%convert ^
  sm_blur2.png ^
  ( +clone ) ^
  -geometry +1+0 ^
  -compose Difference -composite ^
  -fill White +opaque Black ^
  -format %%[fx:mean] +write info: ^
  x0.png

%IM%convert ^
  sm_blur2.png ^
  ( +clone ) ^
  -geometry +0+1 ^
  -compose Difference -composite ^
  -fill White +opaque Black ^
  -format %%[fx:mean] +write info: ^
  x1.png

[rui_liu]

Thank you very much guys, probably I need to redesign my app to see which of the method fits my need.

Currently, I think probably using a light blur looks best (0x10), but since it will keep the original image recognised, I need to find a way to use it as background, since the background is not square, and I don't want to stretch the image.

Thanks~

[fmw42]

I need to find a way to use it as background, since the background is not square, and I don't want to stretch the image.

I do not understand why this is a problem? Blurring the image does not change its size. Can you explain further.

If your image is not the right size, use -resize (with the ^ option) to change the size such that on dimension fits perfectly and the other is slightly too large. Then crop to fit your overlay image.