using (PsdImage image = (PsdImage)Image.Load(sourcePsbFileName))
    {
	    // To open the PSB File as JPG just use this code
        image.Save(sourcePsbFileName + ".jpg",  new JpegOptions());
    }

    public static void convertReadOnlyPSBtoJpeg(String sourceFileName) {
        try {
            PsdLoadOptions loadOptions = new PsdLoadOptions();
            loadOptions.setReadOnlyMode(true);
            
            PsdImage image = null;
            try {
                image = (PsdImage) Image.load(sourceFileName, loadOptions);
                image.save(sourceFileName + ".jpg", new JpegOptions());
            } finally {
                if (image != null) {
                    image.dispose();
                }
            }
        } catch (Exception ex) {

        }
    }

• Examples of opening PSB files on Gists
• Tutorial how to open PSB files without Photoshop
• PSB files viewer as standalone service