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CAD tip CAD tip # 8754:

Question CAD 
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Q - question

Thumbnail settings can influence AutoCAD DWG file size.

A - answer AutoCAD version 2013 has changed the method of storing raster thumbnail images (previews) inside DWG files. These thumbnails are now internally stored in better quality (PNG format) and they have higher default resolution. Windows Explorer or EDM systems working with document thumbnails can now quickly display better pictures of the contents of your DWG drawings.

Size of the thumbnails saved with a drawing is controlled by the THUMBSIZE variable (stored in Registry, default=3). Higher values than the default "3" are by default applied only on 3D drawings. This can be overridden with enabling the variable THUMBSIZE2D.

How does this setting influence the total size of DWG files?

Especially with simple smaller drawings, the increase of the total file size can be quite substantial - up to 2x of the size without any thumbnail (THUMBSAVE=0). The size is also influenced by other factors, e.g. by image compression or by incremental saving of changes into DWGs. The following sample is not influenced by these factors but still consider it an example only:

THUMBSIZEThumb
resolution
File
size
Size
increase
offN/A62 2760%
064 x 6463 555+2.1%
1128 x 12864 579+3.7%
2256 x 25665 603+5.3%
3512 x 51270 723+13.6%
41024 x 102483 011+33.3%
51440 x 144094 275+51.4%
61600 x 160099 395+59.6%
71920 x 1920108 611+74.4%
82560 x 2560132 163+112.2%

In complex DWGs, the total thumbnail (in the largest resolution) can add up to 10MB to the drawing file size.

ACAD2021ACAD2018ACAD2013LT2013DWG
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See also:
Tip 12753:"Local server is loading" when inserting a block in AutoCAD LT.
Tip 10397:How to disable switching drawings when hovering on the DWG tab thumbnail?
Tip 9807:Automatic elevation labels.
Tip 9739:Size of a saved DWG file grows unexpectedly.
Tip 9685:DWG thumbnail is not displayed with some files. Why?


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