Step 1 - Load the snapshot
Okay, before loading the Spellbound snapshot go to File/Preferences/Defaults and make sure you have the following settings: Offset=0, Width=256, Lines=192, Columns=1, Attribute=15 and the Graphics option selected. Once you've done that load the Spellbound snapshot and you should get the display shown in fig 1.1. What you're seeing here is a distorted view of how the screen looked when the snapshot was taken. In this case you can just make out that it's the Spellbound main menu. Why does it look like this? That's because you're seeing the information one byte after the next. This is not how the Speccy stores it screen so the image won't look correct.
fig 1.1
Step 2 - View the snapshot screen memory
Click on the Options button on the snapshot and select Screen Mode, then set the Offset value to 27. Now the view should change to that shown in fig 1.2. This is the screen memory viewed as it should be and thus the image looks fine. The offset is set to 27 to skip over the SNA header information which just so happens to be, you guessed it, 27 bytes long. So what you're seeing here is the memory from 16384 onwards, the screen area, as it was when the snapshot was taken. Note that when viewing in Screen Mode you'll get a colour display. That's because the screen attributes are also taken into account when viewing the memory in this way.
fig 1.2
Step 3 - All I can see is garbage
Set the mode back to Graphics and move back and forth through the snapshot. What you're doing here is altering the start address from where the graphic information is taken. A speccy snapshot is not made up entirely of graphics though. There's also code and data in there. Fig 1.3 shows you how the screen might look if you select an area of memory that is just code. Try moving the Spellbound offset to somewhere around 15000 and this is what you'll see. If you use the drawing tool to alter this type of memory you're snapshot will probably crash when you try and run it on your emulator. Beware before you save any changes.
fig 1.3
Step 4 - Locating graphics
Now let's track down some graphics. Change the offset to read 41167 and you should see the image shown in fig 1.4. At a first glance it appears to be more garbage, but look closer and you'll notice that there are clearly patterns emerging which aren't caused by random bytes of code. This is the first step to locating some graphics and with a little practice you'll reach this stage within seconds of loading the snapshot. So, what next?
fig 1.4
Step 5 - Viewing graphics
The width setting is the most important parameter when it comes to manipulating the display. All games have sprites/blocks of varying widths so it's usually just a case of adjusting this until something appears. Change the width on the Spellbound snapshot to 64 and you'll see two axes as in fig 1.5. Below the axes you can see what are clearly more graphics but as they are a different size you'll need to adjust the width again to view these.
fig 1.5
So that's how easy it is to locate graphics. Not all snapshots files will prove as easy and some you'll find are nigh on impossible. It's all down to how the programmers decided to store their graphics. SGE features five different modes to help you. In addition to the two mentioned above there's also:
Text mode - 8x8 fonts and tiles
Line masks - As in Costa Panayi games (eg. Highway Encounter)
Byte masks - As in Glider Rider
Don't forget that with the drawing tools you can zoom into the images and edit them. Chunks of graphics can be copied and pasted between snapshots although any section that is copied isn't stored on the Windows clipboard so you can't paste into other applications. Any changes you save will appear when you run the snapshot on your emulator.
And to finish with, I'd like to point out that SGE does not support the Z80 format. These snapshots are compressed and therefore any graphics contained within the file will be unrecognisable. SGE was written primarily for SNA files although it should work fine with any non-compressed format.
Have fun.