#776 DWG Preview - DWG bitmap preview colors are very dull ( not vivid)

[jacob unkelman]

i am porting a VBA project to Lisp / open DCL. using a DWG preview object to display dwg's Tumbnail. Colors in VBA are very vivid. not so in OPENDCL.
looking how to improve image quality. see attached doc showing images and source code ( VBA <-> lisp/OPENDCL )

[Owen Wengerd]

How does the built-in file dialog display the preview? How were they created (i.e. from which version of AutoCAD)? Can you attach a small sample?

[jacob unkelman]

Hi Owen,

thanks for the fast respond.
please find attached 2 of the dwg blocks. they were generated by different
autocad version ( 2007 etc). saved as 2000 version.
hope it answered your question.
the problem is with the Thumbnail display. the dwg display is ok but much
more slower ( block object )

and again, thanks for you answer

[Owen Wengerd]

After some experimentation, I've concluded that the problem is primarily due to the algorithm used to shrink the thumbnail image to fit the control canvas. Perhaps you can remedy the situation by sizing the thumbnail images to fit your controls so that no shrinking is necessary. The THUMBSIZE system variable could be useful for that.

I did notice that a simple change in the stretching mode improved the resulting image in the black background case. The next build of OpenDCL will use a different stretch mode when it detects a black background (other background colors will see no change). That small change should improve the situation a little bit.

The thumbnail image processing currently uses the GDI library included with Windows. It's conceivable that third party image processing code could be added in the future, but for now I'm afraid my limited experience with image processing makes further enhancements unlikely.

[jacob unkelman]

Dear Owen.

Thanks for your detailed answer

Jacob Dunkelman
TBM Software Ltd.
Tel: 972-3-5617090 Fax: 972-3-5617093
www.tbm.co.il http://www.tbm.co.il/
Skype: tbm.tbmjacob
https://www.facebook.com/Tbmisrael?fref=ts

---

From: Owen Wengerd [mailto:owenwengerd@users.sf.net]
Sent: Tuesday, June 09, 2015 4:46 AM
To: [opendcl:bugs]
Subject: [opendcl:bugs] #776 DWG Preview - DWG bitmap preview colors are
very dull ( not vivid)

• status: open --> closed-fixed

• assigned_to: Owen Wengerd

• Comment:

After some experimentation, I've concluded that the problem is primarily due
to the algorithm used to shrink the thumbnail image to fit the control
canvas. Perhaps you can remedy the situation by sizing the thumbnail images
to fit your controls so that no shrinking is necessary. The THUMBSIZE system
variable could be useful for that.

I did notice that a simple change in the stretching mode improved the
resulting image in the black background case. The next build of OpenDCL will
use a different stretch mode when it detects a black background (other
background colors will see no change). That small change should improve the
situation a little bit.

The thumbnail image processing currently uses the GDI library included with
Windows. It's conceivable that third party image processing code could be
added in the future, but for now I'm afraid my limited experience with image
processing makes further enhancements unlikely.

---

[bugs:#776] http://sourceforge.net/p/opendcl/bugs/776 DWG Preview - DWG
bitmap preview colors are very dull ( not vivid)

Status: closed-fixed
Group: v 8.0
Labels: DWG Preview
Created: Fri Jun 05, 2015 11:41 AM UTC by jacob unkelman
Last Updated: Fri Jun 05, 2015 08:27 PM UTC
Owner: Owen Wengerd

i am porting a VBA project to Lisp / open DCL. using a DWG preview object to
display dwg's Tumbnail. Colors in VBA are very vivid. not so in OPENDCL.
looking how to improve image quality. see attached doc showing images and
source code ( VBA <-> lisp/OPENDCL )

---

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