Signature Image with Transparent Background

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Joe Winograd
50+ years in computer industry •Everything from development to sales •CIO •Windows •Document Imaging •EE MVE 2015,2016,2018 •EE FELLOW 2017
This article is in response to a question here at Experts Exchange. The Original Poster has a scanned signature and wants to make the background transparent so that the signature may be placed on documents without obliterating the surrounding text. Here's an example of the problem, showing how the surrounding document is overlaid when the non-transparent signature is placed on a PDF (in this case, via the Custom Stamp feature in Adobe Acrobat):

Signing PDF in Acrobat with non-transparent stamp
The solution described in this article requires a product called IrfanView, excellent (and free!) imaging software:

At the URL above, click the Download link on the left to download IrfanView and click the PlugIns link on the left to download the PlugIns, which are needed to give you PDF capability. Installing the PlugIns is optional – required only if you want PDF support (and the other features that come with the PlugIns). Install IrfanView first, then install the PlugIns. Although I recommend adding the PlugIns to get PDF support, that's for general, future usage. For this situation, you don't need them, unless your scanned signature is in a PDF file, in which case you do need them.

Here are the steps for making your signature background transparent after installing IrfanView:

(1) Run IrfanView and open the file that has your scanned signature.

(2) I recommend cropping the signature by dragging the mouse from the upper left to the lower right and selecting the Edit menu, then Crop selection. At that point, you'll have something like this:
John Doe sig not transparent(3) Now save the image as a PNG file, which supports transparency. Click the File menu, then Save as. At the bottom of the Save Picture As dialog, tick the Show options dialog box:

Show options dialog
(4) In the Save as type drop-down, select PNG:

Save as type PNG
(5) You will see a separate window with the PNG/PNM/ICO save options, like this:

PNG save options
(6) I have experimented with various settings in the PNG section of the save options dialog, and I recommend the settings shown in the screenshot above. In particular, Compression level 1, which makes the file larger (but still a reasonable size) and the quality higher, is a good idea for a signature (Compression level 0, i.e. no compression, results in a very large file). Also, I've had success using the transparent signature in more products when Save Transparency as Alpha channel is ticked.

(7) Click Save in the main Save Picture As window. Now the critical step occurs – it will ask you to click in the image to set the transparent color:

Click to set transparent color
So click the mouse on the white background (this assumes, of course, that your scanned signature is dark ink on white paper). After you click the white area, it will be transparent!

(8) Exit IrfanView. The PNG file saved in the step above now has your signature with transparent background.

To show how this works, here is a screenshot of the transparent signature placed on a document, using the same PDF file and the same Custom Stamp feature in Adobe Acrobat that were used with the non-transparent signature at the beginning of this article:

Signing PDF in Acrobat with transparent stamp
If you are wondering how to create a Custom Stamp with your signature in Adobe Acrobat, this EE article explains it:
Create Signature Stamp in Adobe Acrobat

Happy document signing – without having to print it, sign it in ink, and then scan it back in.

If you find this article to be helpful, please click the thumbs-up icon below. This lets me know what is valuable for EE members and provides direction for future articles. Thanks very much! Regards, Joe
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