Minimize Presentation : further quality loss when applying several times?

[bidinou]

Hi everyone !

First post here I recently needed to use the “Minimize Presentation” wizard in Impress when creating a presentation containing many pictures. Obviously, I could have reduced them beforehand but…

The resulting file was several hundreds megabytes large, which, surprisingly, entirely filled the RAM of my computer (8 GB), leading to a system freeze.

→ I figured out using the “minimize presentation” wizard helped significantly reduce the presentation size, RAM usage and sped up the display.

My question is : if I apply the “Minimize presentation” feature several times, does it recompress the images which had been reduced (for ex. to 150 dpi & 75% jpeg quality) – eventually leading to an additional quality loss ?

(use case : after adding a dozen more slides to an already “minimized” presentation…)

Or is the wizard clever enough not to further reduce pictures which had already been reduced ?

Thanks a lot for your help,
best regards,
Bidinou

[Hrbrgr]

@bidinou

eventually leading to an additional quality loss ?

No, I just tested it.

Or is the wizard clever enough…

This has nothing to do with the wizard, but rather with the setting in the wizard.
And only as long as the value is not reduced further (for example 96 dpi, 70%).

[BenAtWork]

Hi @bidinou ,
Although I don’t know the answer to your question per se, another solution comes to mind, depending on what you want to do with it in the end. WHAT I know about the resizer though: you have to set your desired resolution for the images - so, once they are AT that resolution, no further gain can be expected. The only way would be to reduce the resolution further.

Ah - and: the DPI is only for “where to present this?”, it should not effect the size of an image. The only things that matter is the size / dimension of the picture (e.g.2048x… down to e.g. 320x…) and the jpg quality. Think as well about other formats than JPG, as jpg is nice and widely used, but e.g. WebP or AVIF are better for generating smaller sizes. You can convert your pictures with specialized programs (under Windows e.g. IrfanView or under both Windows and Linux consider ImageMagick or GIMP).

Also: do =NOT= simply do a “crop”, as this keeps the WHOLE picture in the presentation, even if only a part is visible. Do a true cut-to-size of the required part of a picture.
Another consideration is NOT to resize the image IN the presentation, but outside, to do a true reduction in size from e.g. 2048 something to e.g. 320 something that fits in the page.
If you insert a HiRes picture, it usually takes the whole page or even goes way outside the page size. Then you “pick” one of the border knots and resizes it to the desired size on the page, to get 2 or 10 picture on the page, right? Well - don’t do that, as, again, the picture SIZE remains within the presentation, only the view of that picture has changed.

Then, when it’s kinda static, with no fancy effects and all - you may consider storing it as PDF instead, as this reduces the size significantly.

And - yeah, it wouldn’t harm (and works better to start with) to go through all the pictures upfront and reduce the sizes. You may check out this for batch processing: Reduce File Size of Images in Linux - CLI and GUI methods | DigitalOcean.

[Hrbrgr]

@BenAtWork

Although I don’t know the answer

And why, then, are you writing in a solution box instead of in a comment?

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[BenAtWork]

Thank you for the RTFM hint. I do believe though that my answer is, in fact, the solution , or, as the button says, a SUGGESTED SOLUTION at least.

[EarnestAl]

If your presentation is intended to be seen on a projector screen and the projector has a maximum resolution of 1920 X 1080 then any extra pixels are wasted. An older projector at 800 X 600 allows for more reduction.
.
Generally, a lower resolution and a reasonable JPG compression will give a better image than high resolution and high JPG compression, especially when projected