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When working with various software more or less related to graphics editing - be it map makers, CAD, 3D modellers or such, I often need to redraw certain contents of some image I have as a bitmap.

It would be extremely helpful if I could place the bitmap in question as overlay on top of the drawing canvas, set its opacity to 50% and then just use the tools of the software I use to replicate the shapes I need. Unfortunately in many cases the software I use doesn't provide ability to put overlays (or use a simple single low-res .jpg as overlay) In this case an external program to display the "overlay" on top of the canvas would be helpful - just drag the image display window over the editor, set the scale right, and edit away! (providing clicking over the image sends the click to the editor, not to the image viewer!)

Example: the newspaper published an infographics with the map of a planned new city car route in my city. I'd like to add it to OpenStreetMap, but the provided map is sketchy at best, denoting a few streets and keeping general proportions but no finer details. I'd be able to overlay it and scale to match street layout, then just draw the route where it's shown on the plan. Unfortunately, OSM editor allows only tileset server for overlays - no simple local file bitmaps.

Requirements:

  • Display image with partial opacity (either settable from the program/fixed or inherent - PNG alpha, I can add this to image myself)
  • pan and scale image to place it precisely (non-essential)
  • don't steal focus when the image is clicked, pass click to window below
  • stay on top, even when the window below is focused.

Note these apply just to the image displayed. What happens to the UI/window/whatever of the viewer application when a different application is focused is irrelevant. I'm open for both free and commercial solutions, Windows preferred but Linux acceptable too.

Is there a program to provide such functionality?

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    For an image: CThruView (Java, GPLv2), Custom Desktop Logo (.NET, Windows, GPLv3). For any window, can be used in conjunction with any image viewer: Peek Through (.NET, Windows, No license). – user Mar 5 '14 at 16:37
  • uh... why did you delete the answers? I couldn't decide which one to choose but it seems like at least CThruView does everything I need. – SF. Mar 6 '14 at 4:44
  • Unfortunately, there creation/content violates the Site Rules. Feel Free to enter discussion Here: meta.softwarerecs.stackexchange.com/questions/735/… – Lyndon White Mar 6 '14 at 8:22
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    If you have found one of these tools fits your needs then you could self answer. With your experience. That would be great. then when others have this problem in future they can read this post – Lyndon White May 29 '14 at 1:40
  • CThruView looks quite cool, but can it be modified to show the image on top of the full-screen apps? – Alexander Shcheblikin Apr 3 '19 at 20:50
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Have a look at OnTopReplica.

It allows you to have a window that is always-on-top. Although it does not let you directly select an image file, you can open the image that you want to work on in any image display program, select that window, and then select the subregion of the window/image that you want shown.

You can then set the opacity to multiples of 25% (Right Click -> Opacity), position the window wherever you want on your screen, then enable click through (Right Click -> Advanced -> Enable Click-Through). You can also scale the window however you like when setting up the capture, as well as save the region of the window you are working on as a "Template" of sorts for other images later.

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Give nomacs a try. It's a free and open-source image editor that does all you require and more!

You can adjust the opacity of the application with Ctrl+J and Ctrl+Shift+J and lock/unlock (to keep on top) the application window with Ctrl+Alt+Shift+B.

I quite like it!

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There is a list of other image transparency utilities on AlternativeTo.net. The list will appear if you search for e.g. CThruView, Image Overlay Utility, or Osiva. The problem is that at present most of the free apps (including these just mentioned) are discontinued - only OnTopReplica seems to be current (or was in 2018). This latter isn't ideal because it cannot rotate images (since it works by a different principle), and it is clumsy in how it turns 'click-through' on and off. But for now, it's the only real 'freeware' choice.

A good transparency viewer really needs to be able to open an image (e.g. jpeg, png) itself; allow manipulation of size, opacity, and rotation by both slider bars and numerical input (to one decimal place); be easy to turn click-through on and off; as well as being able to easily drop the app off the screen onto the taskbar when you want to work unimpeded on the underlying application, which might typically be 3D-CAD or an image editor.

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