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Do Graphics Look Bad When Compressed From ISO to CSO?

Compressing ISO files to CSO format was necessary in the early days of the Sony PlayStation Portable. Memory sticks for this device had a limitation of 1GB, while games were released on Universal Media Discs that were often much larger. To fit these games onto the memory stick, the user compressed them first using third-party software. Memory sticks of today have a much larger capacity, but by using CSO files, users are able to fit more games on one stick. Compressing the files from one format to the other has no impact on the visuals of the game, so the graphics look the same for both formats.

Running ISO Files From a Memory Stick
- PSP games on the original UMD are all saved in the ISO format. The ISO file contains all the game data that the PSP then reads from the UMD and displays on the screen. Unless you are running custom firmware on your PSP, it is not possible to access the ISO file on the UMD directly. With custom firmware, downloadable from sites such as PSP Custom Firmware, Dark Alex and Atma Xplorer, it is possible to copy the ISO file from the UMD to a computer or memory stick for backup purposes. A PSP reads an ISO file faster if it is saved on a memory stick, as it does not have to spin the UMD every time it loads new data. If you use the ISO from a memory stick, you not only get faster loading times but you also conserve battery power. Since ISO files are the native format of the PSP, there is no change to the graphics when you copy the file to the memory stick.
Why Use CSO Files?
- CSO files are compressed versions of ISO files that decrease the file size. The decrease in size can be significant, because in many cases ISO files contain blank spaces known as "dummy" files. This is an anti-piracy measure to artificially increase the size of the game. By stripping out these dummy files and compressing the data, CSO files are much smaller than the original ISO versions. Since the data is compressed and the PSP has to extract the data first, the device might take longer to read CSO files than ISO files but there are no changes to the graphics or audio. The graphics look exactly the same as they did in ISO format.
Compressing an ISO File to CSO Format
- You can only convert an ISO file to the CSO format with computer software and not on the PSP itself. Connect the PSP to a PC using a mini-USB cable before copying the ISO file from the UMD to the hard disk. Free software capable of performing this conversion includes ISO2CSO, ISO-DAX-CSO Converter and YACC. The conversion programs allow for up to nine levels of compression.The more compressed the file is, the slower the PSP reads it, which might introduce lag in the game. The level of compression has no effect on the quality of the graphics, however.
Playing a CSO File on PSP
- After you convert the file, copy it to the ISO folder in the root of the PSP's memory stick to play it. You will then be able to load and play the game as normal using the PSP. This only works on a PSP that is running custom firmware. If you try to open a CSO file on a PSP running official firmware, it displays as corrupted data. You can only legally use CSO files if you are the owner of the original UMD containing the ISO file that was converted. Downloading either ISO or CSO files from the Internet if you are not the original owner is considered software piracy.

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