Bug 107986

Created attachment 133430 [details]
Example file

Telesto: What kind of compression do you use? Which settings do you have made in the dialog?
The embedded image has no dpi information, therefore there exist no "original size" because the size of the pixels is unknown. If you click on "Original size" in step 2, LibreOffice uses an ersatz, likely your screen resolution. Calculate the dpi and use the same dpi in the compression dialog.

I have used:
1. JPG Quality 90:  Reduced image resolution checked set to width  400px, height 529 px and resolution 96 PPI (screen dimensions 10,58x14.00 cm)
2. JPG Quality 90 without reduced image resolution checked
both with same result; a very small image with an apparent dimensions of 0,40 cm x 0,53 cm at 2500 PPI

No issues with the png compression

Apparently LO sets 1px = 1/100 mm. For me LO chooses for the original png-image a size of 8,47cm × 11,22 cm at 120ppi for its 400 pixel × 530 pixel size.

Expected behavior for the jpg image:
 Either
    the same same ersatz value is used for the jpg image and dialog fields are disabled
 or
    the dpi value or width or height respectively, which the user sets in the dialog, is used.

I see this error already in Version: 5.1.6.1
Build ID: f3e25ec0581f5012f54d8810dcddd5824f4ee374
CPU Threads: 4; OS Version: Windows 6.1; UI Render: default; 
Locale: de-DE (de_DE); Calc: group

The image has no dpi set, and uses the same default as the ersatz as the png image and so shows the same size in Version: 4.5.0.0.alpha0+
Build ID: 40b1e8266e47792d354cd457c652bfb0f0a21e69
TinderBox: Win-x86@62-TDF, Branch:MASTER, Time: 2015-02-11_00:13:43
Locale: de_DE

Version: 5.0.0.0.alpha1+
Build ID: e9fbe1f7cd28de2a9da8089d89e903406165eb56
TinderBox: Win-x86@62-merge-TDF, Branch:MASTER, Time: 2015-04-25_00:22:55
Locale: de_DE
sets 96dpi although it is 120dpi for me and I set that is the dialog too.

The fixed for bug 65695 and bug 85761 are likely related.

Would a bibisect be helpful?

(The following is my very naive understanding after 3 days of playing with graphics - but seems to me like NOTABUG.)

I don't expect original size would be from "before a compression". It would be a comparison of the compressed "filesize" with the "display size", wouldn't it? Since the display size can stretch or shrink the actual view size, it is good to know the actual dimensions - particularly for cropping values which are calculations from the original size (if I understand correctly).

Created attachment 160192 [details]
Example2

1. Open the attached file
2. Open the compress Image dialog 
- Actual dimensions 16,93 x 12,70 cm (nothing 'actual'. It's based on my screen)
- The apparent dimensions: 16,93 cm c 12,70 ad 95 DPI (dimension suggest 96 dpi)
3. Reduce image resolution: default settings 2001 width x 1500 Height 300 dpi Lanczos. Jpg compression
4. Press Ok
5. Open the compress dialog again
- Actual dimensions 52,94 cm x 39,69 cm (2001 x 1500px)
- Apparent dimensions: 16,93 x 12,70 cm at 300 dpi
8. Format -> Image -> Properties -> Type Tab
9. Press Original size button (21,00 cm Height x 29,70) -> so limited page size, A4

So lacking DPI setting in file, it's based on screen DPI. However different monitors different DPI settings/image sizes. Corel Paint Shop Pro uses a 'default' settings at 200 DPI for images lacking a resolution. Instead of using the screen resolution as reference.

The different between actual dimensions (suggesting 'real measure') and apparent dimensions quite confusing at minimum. Also what's meant with "apparent" dimensions open for debate, IMHO. Increase the size of the image and the apparent dimensions change (of course) + DPI will be lower. Recompress the image with "Reduce image resolution" at default settings and you have an image of 300 DPI with the same dimensions. 

Always using the apparent resolution would solve a part of the problem. Except I'm not sure what happens on a high DPI screen.. Is there a difference on screen (Writer/Calc/Draw) between the size of the image on 96 dpi and 120 dpi screen?

Another solution would be some random - not screen based setting - at say 200dpi (and an option to change it in Expert configuration), if no resolution is set.

The "actual dimensions" are used the Image Properties Type tab (original size button) as the "original size' which is misleading at minimum.

Dear Telesto,

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