Legacy ImageMagick Discussions Archive

Hi,
I'm trying to create create an image with noise and do it with one combined command, but am having issues.

The image is simply text (i.e. ABCD) and I want to overlay black and white noise to obscure the letters

First creating the text on its own image...

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convert -size 100x100 xc:none  -pointsize 35 -gravity center -draw "text 0,0 'ABCD' " test.png

Next create the black and white noise...

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convert -size 100x100 xc: +noise random -channel G -threshold 25% -negate -channel RG -separate +channel -compose CopyOpacity -composite test2.png

If I want to draw the letters on the noise...

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convert -size 100x100 xc: +noise random -channel G -threshold 25% -negate -channel RG -separate +channel -compose CopyOpacity -composite -pointsize 35 -gravity center -draw "text 0,0 'ABCD' " test3.png

...but this isn't what I want as the noise is under the letters, not over them...

If I reverse the commands however the noise completely covers the letters (as there is no transparency) so I do not see them at all using the following command

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convert -size 100x100 xc:none  -pointsize 35 -gravity center -draw "text 0,0 'ABCD' " xc: +noise random -channel G -threshold 25% -negate -channel RG -separate +channel -compose CopyOpacity -composite test4.png

I tried using -transparent white, but this didn't help. I believe of the xc canvas creation for the noise is swamping the previously defined text. I imagine I need to use parenthesis to separate the layers while they are created and then somehow glue them back together...but I'm not sure how to do it properly.

Can someone please tell me how to correct this, or a better way of accomplishing my goal?

Ammendment: Running 6.9.1 Q16 (64 bit) via DOS command line

Paul.

Probably better approach exists, but following seems to work with 6.9.2-0 Q16 x86 on Windows.
(And also checked with 6.9.0-0 Q16 x86_64 on Mac after converted to proper syntax.)

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convert xc:none[100x100!] ^
 +noise random -channel G -threshold 25% -negate -channel RG -separate +channel ^
 -compose CopyOpacity -composite +write mpr:1 +delete ^
 xc:none[100x100!] -pointsize 35 -gravity center -draw "text 0,0 'ABCD'" ^
 mpr:1 -compose Over -composite test.png

Edit:
After looking a bit, it does not need to be so complex: following is enough (in Unix syntax)

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convert \( xc:none[100x100\!] +noise random -channel G -threshold 25% -negate -channel RG -separate +channel -compose CopyOpacity -composite \) \( xc:none[100x100\!] -pointsize 35 -gravity center -draw "text 0,0 'ABCD'" \) -compose DstOver -composite show:

or

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convert xc:none[100x100\!] \( -clone 0 +noise random -channel G -threshold 25% -negate -channel RG -separate +channel -compose CopyOpacity -composite \) \( -clone 0 -pointsize 35 -gravity center -draw "text 0,0 'ABCD'" \) -delete 0 -compose DstOver -composite show:

Edit 2:
if you want only letter part (like Fred's answer below), replace DstOver to DstIn.

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convert xc:none[100x100\!] \( -clone 0 +noise random -channel G -threshold 25% -negate -channel RG -separate +channel -compose CopyOpacity -composite \) \( -clone 0 -pointsize 35 -gravity center -draw "text 0,0 'ABCD'" \) -delete 0 -compose DstIn -composite show:

If you use gaussian noise, it will add to the base image. Random noise replaces the base image. See -attenuate X +noise gaussian

compare these three results:

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convert -size 500x200 xc:none  -font verdana -pointsize 100 -gravity center -draw "text 0,0 'ABCD'" result1.png

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convert -size 500x200 xc:none  -font verdana -pointsize 100 -gravity center -draw "text 0,0 'ABCD'" -attenuate 5 +noise gaussian result2.png

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convert -size 500x200 xc:none  -font verdana -pointsize 100 -gravity center -draw "text 0,0 'ABCD'" -attenuate 5 +noise gaussian -colorspace gray result3.png

Thank you,
This is just what I was after! As it turns out, I have use for both noise on just the letters and the letters plus the background so this is good and I understand the syntax of grouping operations better now.

Sincerely, Paul.

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