Working with alpha channel

[lorents]

Good evening!
Tell me, please, in the next issue.

There is the original image with an alpha channel.



Beneath the alpha channel is here is a picture



Tell me, how do I do it like this, while preserving the alpha channel of the image.

[snibgo]

I don't understand what you want. Perhaps:

Code: Select all

convert alfThing.png -alpha off -fill White -opaque Black -alpha on a.png

[lorents]

Thank you so much!
I noticed this solution is not suitable for such images here



How can I fix it?

[snibgo]

What result do you want?

[lorents]

I need everything to black under the alpha channel turned white

[lorents]

I need to get out of this picture here is

[snibgo]

The following gives the coordinates of the "bird" image:

Code: Select all

convert bird.png -alpha off -format "%@" info:

From the result, a script can do the rest of the work.

[lorents]

Not quite understand you, if not difficult to please explain in detail.

[snibgo]

The result you want has some pixel colours smeared to the left and right (shown in red), and others are not smeared (shown in green).

What rules say which should be smeared, and which should not?

[lorents]

Here is an image without blurring with a white background



As can be seen the black is present there originally, and that's how to determine that relate to image blur, and what does not define apparently did not happen.

[snibgo]

This smearing effect could easily be done in a process module: loop through the lines; in each line, find the first non-white pixel, copy its values to the white pixels on the left, and similarly for the right-hand side.

I can't see an easy way of doing it at the command-line. It could be done with a complex script that used the same method.

Or a command might build a displacement map, as shown in http://im.snibgo.com/ckbkClut.htm#graph .

Or the white pixels could be made transparent, and a small blur would smear the visible pixels sideways. Repeat until no transparency remains. This method would be imprecise, and slow.

Someone else may have a better method.

[snibgo]

Or we can repeatedly compose over, shifting the bottom image slightly. Windows BAT syntax:

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convert ^
  birdBkW.png ^
  -transparent White ^
  -compose DstOver ^
  ( -clone 0 ) -geometry +1+0 -composite ^
  ( -clone 0 ) -geometry +2+0 -composite ^
  ( -clone 0 ) -geometry +4+0 -composite ^
  ( -clone 0 ) -geometry +8+0 -composite ^
  ( -clone 0 ) -geometry +16+0 -composite ^
  ( -clone 0 ) -geometry +32+0 -composite ^
  ( -clone 0 ) -geometry +64+0 -composite ^
  ( -clone 0 ) -geometry +128+0 -composite ^
  ( -clone 0 ) -geometry -1+0 -composite ^
  ( -clone 0 ) -geometry -2+0 -composite ^
  ( -clone 0 ) -geometry -4+0 -composite ^
  ( -clone 0 ) -geometry -8+0 -composite ^
  ( -clone 0 ) -geometry -16+0 -composite ^
  ( -clone 0 ) -geometry -32+0 -composite ^
  ( -clone 0 ) -geometry -64+0 -composite ^
  ( -clone 0 ) -geometry -128+0 -composite ^
  -background White -compose Over -layers flatten ^
  birdtw.png

birdBkW.png:

birdtw.png

[lorents]

Thank you for choosing
I for some reason is obtained as follows



And is it possible to preserve the transparency image

[snibgo]

What was your exact command? What version of IM are you using? I use v6.9.0-0.


The input file, birdBkW.png, has no transparency.

You could copy the transparency from an image that has transparency:

Code: Select all

convert ^
  birdBkW.png ^
  birdWithTrans.png ^
  -compose CopyOpacity -composite ^
  smearedWithTrans.png

[lorents]

Figured out, I just used, that this image



And you can use the above image, to obtain the same result



But at the same time that the layer alpha channel is preserved?