images ported from odp to pptx dark

Often images in files ported from Libreoffice Impress 5.1 .odp to Powerpoint 2013 .pptx appear very dark. I’m running LibreOffice 5.1 on Ubuntu Linux 16.04, Powerpoint 2013 is running on Windows 10 Home. The Windows computer is old and slow, and I’d rather not use it unless forced.

If I open an .odp file with Powerpoint, then save-as pptx, the effect is worst. Save-as from LibreOffice Impress to pptx is better, but the effect is still there (along with the other usual mess that happens when you try to work with Powerpoint and Impress on the same file … which I’ve learned to live with.)

Currently, the best fix I could have come up with is to go to each slide, in Power point, and delete the images one-by-one, then re-insert the same image from the same file. Then the image appears normally bright in Powerpoint. This is of course tedious on a large presentation.

I’m getting ready to teach an 8 hour course, with a slide per minute, and I really don’t want to have to edit all those images. I’ve found old messages about this issue, and the recommendation was to upgrade, but I have experienced this issue with these two programs continuously since at least 2011.

In the past I’ve had to ditch LibreOffice Impress, and just work in clunky PowerPoint, to solve this problem, a non-ideal solution.

However, I’ve done several experiments and found the worst method is to open an .odp file with Powerpoint, which makes all the pictures much darker than the original, and with the current versions of these two software packages I have, Libreoffice exports (via Save-As) cleanly to .pptx and .ppt formats which can them be opened in Powerpoint. So it looks like the first fix is to NOT open anything with Powerpoint except in it’s native format. Use Libreoffice Save-as to export. This is at least acceptable for me.

But there might be a better solution. Does anyone else grapple with dark images in ported files?

I remember that there had been some differences between PowerPoint and LibreOffice about the meaning of the percent value in Brightness. But I have got PowePoint 2016 and LibreOffice 6 now and have no problems.

I’m running into the same problem with Powerpoint 2013 (desktop installation). The following effortless VBA solution works well (completely well, as far as I can tell).

From Dark pictures in ODT document from LibreOffice - Microsoft Community :

Public Sub CorrectAllPicsBrightness()
  Dim sld As Slide
  Dim i As Long
  For Each sld In ActivePresentation.Slides
   For i = sld.Shapes.Count To 1 Step -1
     If sld.Shapes(i).Type = msoPicture Then
       sld.Shapes(i).PictureFormat.Brightness = 0.5  'magic number after some trials.
     End If
End Sub