#776 Official DCX sample file cannot be read from GraphicsMagick

[Jaroslav Fojtik]

Graphics Magick refuses to load official DCX sample image listed here:
http://justsolve.archiveteam.org/wiki/DCX

D:\temp\30>gm.exe identify SAMPLE.DCX 
gm.exe identify: Improper image header (SAMPLE.DCX).
gm.exe identify: Request did not return an image.

I have analyzed file and it looks fine without any problems. My own tool can read it without any problems. It looks that .DCX reader implementation is faulty.

D:\temp\30>gconvert SAMPLE.DCX SAMPLE.png
 <<< GCONVERT >>> Convert picture format (c)1997-2026 F&TSoft, version 2.85
Loading
OK

[Jaroslav Fojtik]

Converted .DCX from my utility as a reference.

Please note .DCX fileformat chart: https://formats.kaitai.io/pcx_dcx/

[Bob Friesenhahn]

I notice that latest ImageMagick 7 also cannot read this DCX file.

In GM, the (initial?) problem seems related to a bytes-per-line value which is computed based on multiplying columns and bits-per-pixel. This file computes 216, but the code requires at least 217.

[Bob Friesenhahn]

Where can we find the source code for your utility?

[Jaroslav Fojtik]

I do not understand this limit. I do not remember to implement something like this.

You can get my utility from here: https://ftsoft.com.cz/pictures/pictures.html
It can be compiled under Linux, but it was not so heavily tested.

[Bob Friesenhahn]

I discovered that many DCX files can no longer be read due to a problematic file size sanity check. I have committed a fix for that file size check. Unfortunately, the issue reported here is due to a different check.

[Jaroslav Fojtik]

Here you can find several DCX images to test: https://sembiance.com/fileFormatSamples/image/dcx/
PCX/DCX standard does not specify sanity checks.

[Bob Friesenhahn]

The link you referenced was where I found several very useful DCX files,
including some which suffer from the same bug you reported.

On Fri, Sep 11, 2026, 4:11 PM Jaroslav Fojtik fojtik@users.sourceforge.net
wrote:

Here you can find several DCX images to test:
https://sembiance.com/fileFormatSamples/image/dcx/
PCX/DCX standard does not specify sanity checks.

---

[bugs:#776] https://sourceforge.net/p/graphicsmagick/bugs/776/ Official
DCX sample file cannot be read from GraphicsMagick

Status: open
Group: v1.0_(example)
Created: Fri Sep 11, 2026 06:11 PM UTC by Jaroslav Fojtik
Last Updated: Fri Sep 11, 2026 10:05 PM UTC
Owner: nobody
Attachments:

• SAMPLE.DCX
  https://sourceforge.net/p/graphicsmagick/bugs/776/attachment/SAMPLE.DCX
  (sourceforge.net) (44.0 kB; application/octet-stream)

Graphics Magick refuses to load official DCX sample image listed here:
http://justsolve.archiveteam.org/wiki/DCX

D:\temp\30>gm.exe identify SAMPLE.DCX gm.exe identify: Improper image header (SAMPLE.DCX).gm.exe identify: Request did not return an image.

I have analyzed file and it looks fine without any problems. My own tool
can read it without any problems. It looks that .DCX reader implementation
is faulty.

D:\temp\30>gconvert SAMPLE.DCX SAMPLE.png
<<< GCONVERT >>> Convert picture format (c)1997-2026 F&TSoft, version 2.85
Loading
OK

---

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