Replace transparency in PNG images with white background

Question

I've got some PNG images with transparency, and I need to create versions with the image layer composed onto a white background. I've tried various things with Image Magick "convert" operations, but either nothing happens at all or I get an error. I don't want to go to an intermediate JPG form because I don't want the artifacts. Of course it's easy to do this in Gimp or Photoshop or whatever, but I'd really rather script it from the command line because there are many of these things.

An example of a non-working Image Magick command is:

convert img1.png -background white -flatten img1-white.png

That results in an error.

Thanks!

In my specific case the transparency layer in PNG conflicted when going through a (Apache) FO processor to create a PDF/A. PDF/A does not allow transparency. The hack I used is to turn to JPG instead. — Wivani, May 19 '14 at 12:03
That command should work fine. If it does not, then you may have a buggy install of Imagemagick or libpng or your versions of either are too old. What is your version of Imagemagick and libpng? — fmw42, Sep 12 '18 at 16:41

Rok Kralj · Answer 1 · 2019-03-27T22:48:09.133

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-background white -alpha remove -alpha off

Example:

convert image.png -background white -alpha remove -alpha off white.png

Feel free to replace white with any other color you want. Imagemagick documentation says this about the -alpha remove operation:

This operation is simple and fast, and does the job without needing any extra memory use, or other side effects that may be associated with alternative transparency removal techniques. It is thus the preferred way of removing image transparency.

edited Mar 27 '19 at 22:48

answered Dec 08 '11 at 20:53

Rok Kralj

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may be it doesnt work anymore on 2014? my transparent background png did not merge, it just got overwritten and I lost the background file (I had a backup btw) – Aquarius Power Jun 30 '14 at 18:28
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I have edited this answer on 2014-09-08. Feel free to try it again. – Rok Kralj Sep 08 '14 at 13:00
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Seems that `-background white` is not needed (it likely is for other colors though). – Skippy le Grand Gourou Oct 13 '15 at 15:23
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@SkippyleGrandGourou: It is needed, as the transparency fallback color for PNG is not always white. – Rok Kralj Oct 14 '15 at 11:35
How would you change that one-liner to batch-convert all *.png in a given folder? – nutty about natty Sep 25 '16 at 09:51
it is work on I convert pdf to tiff `convert file1.pdf -resize 1728x2255 -background white -alpha remove -monochrome -units PixelsPerInch -density 204x196 -compress Fax lsb img2.tiff` thank you – Tarek Kalaji Nov 01 '16 at 09:06
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@nuttyaboutnatty Try this: find /your/path -name "*.png" -exec convert {} -background white -alpha remove {}.white.png \; – MiniQuark Jan 27 '17 at 14:37
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better than the accepted answer (which in case of more than one layer doesn't do the right thing) – axkibe Sep 28 '17 at 13:01
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@nuttyaboutnatty, you could try the morgrify command (installed with imagemagic: mogrify -background white -alpha remove *.png – Allan Nienhuis Dec 07 '17 at 23:58
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The resulting image will still have an alpha channel. It will be empty but it will still be there. To completely remove the channel add `-alpha off`. – josch Mar 27 '18 at 06:46
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Doesn't work. I made a new PNG with a transparent background and a red dot in the middle. Always produced a black background, no matter what color I specified. `convert image.png -background white -alpha off white.png` produced an image with a black background. `convert image.png -background "#00ff33" -alpha off 00ff33.png` produced a black background – McNulty Dec 17 '18 at 04:38
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As an additional step I ran the "pngcrush" program on the results. This shaved the final file size back down to the same size as the original. – Dan Jacobson 積丹尼 Aug 06 '19 at 14:09
For available colours see here: https://imagemagick.org/script/color.php – holzkohlengrill Jan 21 '21 at 16:42
Potentially you would like a boder too: `-border 7 -bordercolor white` – holzkohlengrill Jan 21 '21 at 17:00
@mcnutty I had a similar problem. It seems that (as per the comment from @josch) you need `-alpha remove` before `-alpha off`. So your sequence should be `convert image.png -background white -alpha remove -alpha off white.png`. – Rhubbarb Apr 23 '21 at 22:39

score 292 · Accepted Answer · edited Sep 21 '16 at 16:34

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This works for me:

convert -flatten img1.png img1-white.png

Documentation references:

-flatten command-line option
-layers command-line option (-flatten is equivalent to -layers flatten)

edited Sep 21 '16 at 16:34

Flimm

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answered Feb 24 '10 at 00:27

remosu

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Somehow this doesn't work for me... I tried "-transparent-color white", but got an exception/warning. – William Niu Aug 09 '10 at 04:49
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It turns out that I need to set the -background to white as well. I also had to download the colors.xml, which was missing. – William Niu Aug 09 '10 at 04:59
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Check out my answer below. It was added 2 years after this one. – Rok Kralj Apr 03 '13 at 08:34
may be it doesnst work anymore on 2014? it overwrite the background with the main image one – Aquarius Power Jun 30 '14 at 18:32
On the Mac, open Automator, create a new 'Run Shell Script' action and then add this to it: for f in "$@" do /opt/local/bin/convert -flatten "$f" "$f" done Save this as a service and now you can simply right click on any file(s) to remove alpha. – strangetimes Mar 22 '15 at 14:48
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**DO NOT** try to convert multi-page documents with `-flatten`. It will flatten the pages into one page. – Tim S. May 28 '15 at 15:39
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If you want to do it on all files from your folder you can do it this way: `mogrify -flatten *.png` just in case, do not forget to do backup. More info here: https://www.imagemagick.org/script/mogrify.php – tro Jun 22 '17 at 17:28
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I tried `-flatten` in a batch command and all the images got super-imposed into 1 image. Next I tried `-background white -alpha remove` and it worked, in batch mode. – Yan King Yin Aug 17 '18 at 15:35
this does seem to reduce the quality of the image. – BraveHeart Feb 02 '20 at 12:37

score 46 · Answer 3 · answered Jun 06 '11 at 15:13

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Flattening image and applying background image is straight forward in ImageMagick

However, order of the commands is very important

To apply any background on a transparent image and flatten it, first apply the background than flatten it. The reverse doesn't work.

$ convert sourceimage.png -background BackgroundColor -flatten destinationimage.png

answered Jun 06 '11 at 15:13

acpmasquerade

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For whatever reason, this worked fine for me. Not sure why your original attempt didn't work. – Anthony Mar 26 '14 at 05:10

score 23 · Answer 4 · answered Feb 16 '15 at 03:51

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The only one that worked for me was a mix of all the answers:

convert in.png -background white -alpha remove -flatten -alpha off out.png

answered Feb 16 '15 at 03:51

db0

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Cool, that worked. I actually needed another color than white and you can use `... -background "#010203" ...` instead of using white. – Alexis Wilke May 01 '15 at 23:18
here's how to replace the same image in all folders in a directory `mogrify -background white -flatten */*.png` – Julian Sep 28 '16 at 01:53
`-alpha remove` was what did it for me – Stefan Dragnev Nov 15 '18 at 14:07

score 15 · Answer 5 · answered Sep 28 '16 at 04:04

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here's how to replace the same image in all folders in a directory with white instead of transparent:

mogrify -background white -flatten */*.png

answered Sep 28 '16 at 04:04

Julian

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score 10 · Answer 6 · answered Apr 21 '14 at 10:07

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Using -flatten made me completely mad because -flatten in combination with mogrify crop and resizing simply doesn't work. The official and for me only correct way is to "remove" the alpha channel.

-alpha remove -alpha off (not needed with JPG)

See documention: http://www.imagemagick.org/Usage/masking/#remove

answered Apr 21 '14 at 10:07

Tjarko Rikkerink

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so how would become the command? this did not work here: `convert imgWithTranspBkg.png -alpha remove -alpha off bkg.jpg resultImg.png` – Aquarius Power Jun 30 '14 at 18:39
I only wanted to remove alpha. Convert to JPG did it, nice and easy. Thanks for the tip. – Roger C S Wernersson Nov 14 '14 at 12:18
This is the only solution of the above that worked for me. Now the iTunes store is happy with my image. – Bill Cheswick Jan 02 '15 at 03:34

score 7 · Answer 7 · answered Jun 22 '16 at 16:37

The Alpha Remove section of the ImageMagick Usage Guide suggests using the -alpha remove option, e.g.:

convert in.png  -background white  -alpha remove  out.png

...using the -background color of your choosing.

The guide states:

This operation is simple and fast, and does the job without needing any extra memory use, or other side effects that may be associated with alternative transparency removal techniques. It is thus the prefered way of removing image transparency.

It additionally adds the note:

Note that while transparency is 'removed' the alpha channel will remain turned on, but will now be fully-opaque. If you no longer need the alpha channel you can then use Alpha Off to disable it.

Thus, if you do not need the alpha channel you can make your output image size smaller by adding the -alpha off option, e.g:

convert in.png  -background white  -alpha remove  -alpha off  out.png

There are more details on other, often-used techniques for removing transparency described in the Removing Transparency from Images section.

Included in that section is mention of an important caveat to the usage of -flatten as a technique for removing transparency:

However this will not work with "mogrify" or with a sequence of multiple images, basically because the "-flatten" operator is really designed to merge multiple images into a single image.

So, if you are converting several images at once, e.g. generating thumbnails from a PDF file, -flatten will not do what you want (it will flatten all images for all pages into one image). On the other hand, using the -alpha remove technique will still produce multiple images, each one having transparency removed.

score 5 · Answer 8 · answered Jul 01 '13 at 11:10

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It appears that your command is correct so the problem might be due to missing support for PNG (). You can check with convert -list configure or just try the following:

sudo yum install libpng libpng-devel

answered Jul 01 '13 at 11:10

Alastair

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Yes, thanks; this (old) issue was a bug in "graphicks magick", which is a fork/rewrite/whatever of "image magick'. – Pointy Jul 01 '13 at 13:40
@Pointy I see! Out of curiosity, what was the actual cause of the issue (that was only in one version)? – Alastair Jul 02 '13 at 02:24
Well I really don't know exactly; it was just a bug. I'm not a maintainer of Graphicks Magick so I have no insight into their code. I need to try again at some point I guess. – Pointy Jul 02 '13 at 03:11
ubuntu doesnt have it? here is libpng12-0 but still doesnt work :( – Aquarius Power Jun 30 '14 at 18:36
I'm using Ubuntu 13.04 with `libpng12-0` installed and working. Can you see png if you run this? `convert -list configure | grep \png` – Alastair Jul 08 '14 at 10:49

score 5 · Answer 9 · answered Apr 17 '15 at 08:22

This is not exactly the answer to your question, but I found your question while trying to figure out how to remove the alpha channel, so I decided to add this answer here:

If you want to remove alpha channel using imagemagick, you can use this command:

mogrify -alpha off ./*.png

Pointy · Answer 10 · 2013-05-17T20:42:57.667

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Welp it looks like my decision to install "graphics magick" over "image magick" has some rough edges - when I reinstall genuine crufty old "image magick", then the above command works perfectly well.

edit, a long time later — One of these days I'll check to see if "graphics magick" has fixed this issue.

edited May 17 '13 at 20:42

answered Feb 24 '10 at 00:21

Pointy

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McNulty · Answer 11 · 2018-12-17T05:32:28.053

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I needed either: both -alpha background and -flatten, or -fill.

I made a new PNG with a transparent background and a red dot in the middle.

convert image.png -background green -alpha off green.png failed: it produced an image with black background

convert image.png -background green -alpha background -flatten green.png produced an image with the correct green background.

Of course, with another file that I renamed image.png, it failed to do anything. For that file, I found that the color of the transparent pixels was "#d5d5d5" so I filled that color with green:

convert image.png -fill green -opaque "#d5d5d5" green.png replaced the transparent pixels with the correct green.

edited Dec 17 '18 at 05:32

answered Dec 17 '18 at 04:48

McNulty

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the proper command with current ImageMagick would be `convert image.png -background green -alpha background -alpha off green.png` or `convert image.png -background green -alpha background -alpha remove green.png` or `convert image.png -background green -flatten green.png` – fmw42 Dec 17 '18 at 06:35

Aquarius Power · Answer 12 · 2014-07-09T08:52:13.013

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this creates an image just placing the 1st with transparency on top of the 2nd

composite -gravity center ImgWithTransp.png BackgroundSameSizeOfImg.png ResultImg.png

originally found the tip on this post

edited Jul 09 '14 at 08:52

answered Jun 30 '14 at 18:46

Aquarius Power

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score 0 · Answer 13 · answered Sep 09 '14 at 15:41

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To actually remove the alpha channel from the file, use the alpha off option:

convert in.png -background white -alpha off out.png

answered Sep 09 '14 at 15:41

Nick Dowell

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Actually, the link you provided says: "It does not actually delete or destory the alpha channel attached to the image, it just turns off any effect that channel has on the image." To really remove the alpha channel, see my answer. – Rok Kralj Nov 06 '15 at 09:09

score 0 · Answer 14 · answered Sep 12 '18 at 15:52

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I saw this question and answers which really help me but then I was needed to do it for a lot of files, So in case you have multiple images (PNG images) in one folder and you want to do it for all:

find ./ -name "*.png" -exec convert {} -flatten {} \;

answered Sep 12 '18 at 15:52

talsibony

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score -1 · Answer 15 · answered Nov 13 '18 at 23:54

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It's -alpha off, NOT -alpha remove! iOS app store upload fails when there is an alpha channel in any icon!!

Here's how to do it: mogrify -alpha off *.png

answered Nov 13 '18 at 23:54

railsfanatic

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hbere · Answer 16 · 2021-04-14T13:46:36.557

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This does the job for me:

magick convert OLD.png -background white -alpha remove NEW.png

Here is a starter image with a transparent background in case it helps with testing:

Also, for one-offs on PC, you can always open the PNG file in Windows Paint and click Save. This will automatically turn the transparency to opaque white.

edited Apr 14 '21 at 13:46

answered Feb 12 '20 at 23:02

hbere

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Replace transparency in PNG images with white background

16 Answers16

Documentation references:

Linked