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Set alpha according to gradient with imagemagick

Imagemagick gradient from left and rightHow do I set a colour to be transparent in a GIF using ImageMagick?Changing a pixel's alpha value with imagemagickImageMagick: How to set transparency color of an opaque overlay before composite?Imagemagick: replace alpha pixel with color-shade pixelImageMagick convert - Label text over alpha backgroundConvert to gray 1-bit, alpha 8-bit with ImageMagickApply gradient mask on image that already has transparency with ImageMagick?imagemagick mean image sequence and ignore alpha channelImagick equivalent of the following ImageMagick code

.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty margin-bottom:0;

0

Is it possible to set the alpha channel of an image according to a gradient with ImageMagick?

I'd like the pixels on the left border of an image to be 100% transparent, and the ones on the right border to be 100% opaque, and with the ones in the middle having progressively lower transparency values.

Or in a more general case - given a grayscale image, set the alpha channel of another image as a function of the B&W values (black = 100% alpha, white 0% alpha).

imagemagick

share|improve this question

edited Mar 27 at 11:47

Salomon Zhang

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asked Mar 27 at 11:36

simonesimone

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add a comment | 

0

Is it possible to set the alpha channel of an image according to a gradient with ImageMagick?

I'd like the pixels on the left border of an image to be 100% transparent, and the ones on the right border to be 100% opaque, and with the ones in the middle having progressively lower transparency values.

Or in a more general case - given a grayscale image, set the alpha channel of another image as a function of the B&W values (black = 100% alpha, white 0% alpha).

imagemagick

share|improve this question

edited Mar 27 at 11:47

Salomon Zhang

1,20022 gold badges1717 silver badges2828 bronze badges

asked Mar 27 at 11:36

simonesimone

1,55911 gold badge1414 silver badges2828 bronze badges

add a comment | 

Is it possible to set the alpha channel of an image according to a gradient with ImageMagick?

I'd like the pixels on the left border of an image to be 100% transparent, and the ones on the right border to be 100% opaque, and with the ones in the middle having progressively lower transparency values.

Or in a more general case - given a grayscale image, set the alpha channel of another image as a function of the B&W values (black = 100% alpha, white 0% alpha).

imagemagick

share|improve this question

edited Mar 27 at 11:47

Salomon Zhang

1,20022 gold badges1717 silver badges2828 bronze badges

asked Mar 27 at 11:36

simonesimone

1,55911 gold badge1414 silver badges2828 bronze badges

share|improve this question

edited Mar 27 at 11:47

Salomon Zhang

1,20022 gold badges1717 silver badges2828 bronze badges

asked Mar 27 at 11:36

simonesimone

1,55911 gold badge1414 silver badges2828 bronze badges

share|improve this question

edited Mar 27 at 11:47

Salomon Zhang

1,20022 gold badges1717 silver badges2828 bronze badges

asked Mar 27 at 11:36

simonesimone

1,55911 gold badge1414 silver badges2828 bronze badges

edited Mar 27 at 11:47

Salomon Zhang

1,20022 gold badges1717 silver badges2828 bronze badges

edited Mar 27 at 11:47

Salomon Zhang

1,20022 gold badges1717 silver badges2828 bronze badges

asked Mar 27 at 11:36

simonesimone

1,55911 gold badge1414 silver badges2828 bronze badges

asked Mar 27 at 11:36

simonesimone

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2 Answers
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With ImageMagick you can use "-sparse-color" to apply a gradient only to the alpha channel to get the result you describe.

convert in.png -alpha set -background none -channel A 
 -sparse-color barycentric "0,0 none %[w],0 white" +channel out.png

That command starts by activating the alpha channel and setting the background color to transparent. Then it uses "-channel A" to apply the following operation only to the alpha channel. The "-sparse-color" operation tells it to start with transparent at the far left edge, pixel "0,0" and graduate to opaque at pixel "%[w],0". The "%[w]" means the width or far right edge.

Although there are many ways to accomplish the effect you've described, by using "-sparse-color" you can easily make the gradient start and end at any positions on the image without having to create any intermediate masking images.

share|improve this answer

edited Mar 27 at 14:58

answered Mar 27 at 14:44

GeeMackGeeMack

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2

Simple. You would use -composite CopyOpacity to set the alpha channel from a gradient mask.

Given I have the following images. image.png & transparent_mask.png

We can set the image transparency (where black is alpha, and white is opaque) by copying values from the mask image to the input image alpha channel.

convert image.png transparent_mask.png -compose CopyOpacity -composite output.png

share|improve this answer

answered Mar 27 at 12:37

emcconvilleemcconville

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0

With ImageMagick you can use "-sparse-color" to apply a gradient only to the alpha channel to get the result you describe.

convert in.png -alpha set -background none -channel A 
 -sparse-color barycentric "0,0 none %[w],0 white" +channel out.png

That command starts by activating the alpha channel and setting the background color to transparent. Then it uses "-channel A" to apply the following operation only to the alpha channel. The "-sparse-color" operation tells it to start with transparent at the far left edge, pixel "0,0" and graduate to opaque at pixel "%[w],0". The "%[w]" means the width or far right edge.

Although there are many ways to accomplish the effect you've described, by using "-sparse-color" you can easily make the gradient start and end at any positions on the image without having to create any intermediate masking images.

share|improve this answer

edited Mar 27 at 14:58

answered Mar 27 at 14:44

GeeMackGeeMack

1,62611 gold badge33 silver badges66 bronze badges

add a comment | 

0

With ImageMagick you can use "-sparse-color" to apply a gradient only to the alpha channel to get the result you describe.

convert in.png -alpha set -background none -channel A 
 -sparse-color barycentric "0,0 none %[w],0 white" +channel out.png

That command starts by activating the alpha channel and setting the background color to transparent. Then it uses "-channel A" to apply the following operation only to the alpha channel. The "-sparse-color" operation tells it to start with transparent at the far left edge, pixel "0,0" and graduate to opaque at pixel "%[w],0". The "%[w]" means the width or far right edge.

Although there are many ways to accomplish the effect you've described, by using "-sparse-color" you can easily make the gradient start and end at any positions on the image without having to create any intermediate masking images.

share|improve this answer

edited Mar 27 at 14:58

answered Mar 27 at 14:44

GeeMackGeeMack

1,62611 gold badge33 silver badges66 bronze badges

add a comment | 

With ImageMagick you can use "-sparse-color" to apply a gradient only to the alpha channel to get the result you describe.

convert in.png -alpha set -background none -channel A 
 -sparse-color barycentric "0,0 none %[w],0 white" +channel out.png

That command starts by activating the alpha channel and setting the background color to transparent. Then it uses "-channel A" to apply the following operation only to the alpha channel. The "-sparse-color" operation tells it to start with transparent at the far left edge, pixel "0,0" and graduate to opaque at pixel "%[w],0". The "%[w]" means the width or far right edge.

Although there are many ways to accomplish the effect you've described, by using "-sparse-color" you can easily make the gradient start and end at any positions on the image without having to create any intermediate masking images.

share|improve this answer

edited Mar 27 at 14:58

answered Mar 27 at 14:44

GeeMackGeeMack

1,62611 gold badge33 silver badges66 bronze badges

convert in.png -alpha set -background none -channel A 
 -sparse-color barycentric "0,0 none %[w],0 white" +channel out.png

share|improve this answer

edited Mar 27 at 14:58

answered Mar 27 at 14:44

GeeMackGeeMack

1,62611 gold badge33 silver badges66 bronze badges

answered Mar 27 at 14:44

GeeMackGeeMack

1,62611 gold badge33 silver badges66 bronze badges

answered Mar 27 at 14:44

GeeMackGeeMack

1,62611 gold badge33 silver badges66 bronze badges

2

Simple. You would use -composite CopyOpacity to set the alpha channel from a gradient mask.

Given I have the following images. image.png & transparent_mask.png

We can set the image transparency (where black is alpha, and white is opaque) by copying values from the mask image to the input image alpha channel.

convert image.png transparent_mask.png -compose CopyOpacity -composite output.png

share|improve this answer

answered Mar 27 at 12:37

emcconvilleemcconville

17.3k33 gold badges3535 silver badges4747 bronze badges

add a comment | 

2

Simple. You would use -composite CopyOpacity to set the alpha channel from a gradient mask.

Given I have the following images. image.png & transparent_mask.png

We can set the image transparency (where black is alpha, and white is opaque) by copying values from the mask image to the input image alpha channel.

convert image.png transparent_mask.png -compose CopyOpacity -composite output.png

share|improve this answer

answered Mar 27 at 12:37

emcconvilleemcconville

17.3k33 gold badges3535 silver badges4747 bronze badges

add a comment | 

Simple. You would use -composite CopyOpacity to set the alpha channel from a gradient mask.

Given I have the following images. image.png & transparent_mask.png

We can set the image transparency (where black is alpha, and white is opaque) by copying values from the mask image to the input image alpha channel.

convert image.png transparent_mask.png -compose CopyOpacity -composite output.png

share|improve this answer

answered Mar 27 at 12:37

emcconvilleemcconville

17.3k33 gold badges3535 silver badges4747 bronze badges

convert image.png transparent_mask.png -compose CopyOpacity -composite output.png

share|improve this answer

answered Mar 27 at 12:37

emcconvilleemcconville

17.3k33 gold badges3535 silver badges4747 bronze badges

answered Mar 27 at 12:37

emcconvilleemcconville

17.3k33 gold badges3535 silver badges4747 bronze badges

answered Mar 27 at 12:37

emcconvilleemcconville

17.3k33 gold badges3535 silver badges4747 bronze badges