![[GUIDE] How to Shrink GDI images for Dreamcast / Flycast @DemiGodX](https://i.ytimg.com/vi/kPNrJRBtS6E/maxresdefault.jpg)
Uploaded October 2025 | Updated September 2026, 2 weeks ago
πππ’π: after further testing it appears the chd issue was mainly a issue with my USB stick. I tested the CVS2 chd on my main ext4 USB and it plays it the same as gdi. Still the guide below is useful for those who want to shrink gdi.
As some of you know, Dreamcast GDI and CDI images are very large, they're usually always 1.10 GB or 700MB if it's in the CDI format. The reason is because they would pad the disc to expand it to the maximum size of the disc.
CHD compression is good at reducing the size but it can cause a performance hit on some games. In this video you'll notice frequent pauses in Capcom vs SNK 2 when it's compressed with chd. when it's uncompressed with GDI it plays much smoother.
A solution to this is to shrink the GDI to remove the dummy data. It won't be as small as chd but it's uncompressed and in the case of CVS2 it shunk it down to 226mb which is what it would be without the dummy data.
Here are the tools needed to shrink a GDI image
gditools: github.com/einsteinx2/gditools
Python 2.7: python.org/download/releases/2.7
Basically download gditools by clicking Code π‘ Download Zip, then extract the gditools-master.zip.
Next install Python 2.7, once that's done copy your Dreamcast game folder into the gditools-master folder, finally double click on shrink_all.bat and follow the on screen instructions and it'll automatically shrink your game
πππ’π: after further testing it appears the chd issue was mainly a issue with my USB stick. I tested the CVS2 chd on my main ext4 USB and it plays it the same as gdi. Still the guide below is useful for those who want to shrink gdi.
As some of you know, Dreamcast GDI and CDI images are very large, they're usually always 1.10 GB or 700MB if it's in the CDI format. The reason is because they would pad the disc to expand it to the maximum size of the disc.
CHD compression is good at reducing the size but it can cause a performance hit on some games. In this video you'll notice frequent pauses in Capcom vs SNK 2 when it's compressed with chd. when it's uncompressed with GDI it plays much smoother.
A solution to this is to shrink the GDI to remove the dummy data. It won't be as small as chd but it's uncompressed and in the case of CVS2 it shunk it down to 226mb which is what it would be without the dummy data.
Here are the tools needed to shrink a GDI image
gditools: github.com/einsteinx2/gditools
Python 2.7: python.org/download/releases/2.7
Basically download gditools by clicking Code π‘ Download Zip, then extract the gditools-master.zip.
Next install Python 2.7, once that's done copy your Dreamcast game folder into the gditools-master folder, finally double click on shrink_all.bat and follow the on screen instructions and it'll automatically shrink your game
![[GUIDE] How to Shrink GDI images for Dreamcast / Flycast](https://i.ytimg.com/vi/kPNrJRBtS6E/mqdefault.jpg "[GUIDE] How to Shrink GDI images for Dreamcast / Flycast
πππ’π: after further testing it appears the chd issue was mainly a issue with my USB stick. I tested the CVS2 chd on my main ext4 USB and it plays it the same as gdi. Still the guide below is useful for those who want to shrink gdi.
As some of you know, Dreamcast GDI and CDI images are very large, theyre usually always 1.10 GB or 700MB if its in the CDI format. The reason is because they would pad the disc to expand it to the maximum size of the disc.
CHD compression is good at reducing the size but it can cause a performance hit on some games. In this video youll notice frequent pauses in Capcom vs SNK 2 when its compressed with chd. when its uncompressed with GDI it plays much smoother.
A solution to this is to shrink the GDI to remove the dummy data. It wont be as small as chd but its uncompressed and in the case of CVS2 it shunk it down to 226mb which is what it would be without the dummy data.
Here are the tools needed to shrink a GDI image
gditools: https://github.com/einsteinx2/gditools
Python 2.7: https://www.python.org/download/releases/2.7/
Basically download gditools by clicking Code π‘ Download Zip, then extract the gditools-master.zip.
Next install Python 2.7, once thats done copy your Dreamcast game folder into the gditools-master folder, finally double click on shrink_all.bat and follow the on screen instructions and itll automatically shrink your game")
