SCP file shrinking

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Radiorama
Posts: 8
Joined: Mon Jan 18, 2021 9:51 am

SCP file shrinking

Post by Radiorama »

Hello Jeff,

I'm more and more impressed every day by the power of the HxC Floppy Emulator software. Today I managed to repair a disk image that had a few bad sectors. I was able to reconstruct what the correct data should have looked like, so I wrote a simple script to convert those hex bytes to MFM, and using the direct editing function I was able to tweak a few flux reversals until the bad sectors turned from red to green. Brilliant!

I have a question, though. The original disk image with the bad sectors was acquired through Greaseweazle in SCP format, and I noticed that every time I saved a copy the file size would shrink. The original SCP was 17 MB, I edited a sector and saved it and got 13 MB, then loaded it again and edited another sector and got a 10 MB SCP. Does HxC Floppy Emulator discard some data, possibly redundant, whenever an image is saved?

To save I use the Export function, is there another way like a save button to save the exact file I'm editing with only the few modifications?

Thanks and all the best,
Radiorama

Jeff
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Re: SCP file shrinking

Post by Jeff »

Can you share the image ?

Radiorama
Posts: 8
Joined: Mon Jan 18, 2021 9:51 am

Re: SCP file shrinking

Post by Radiorama »

Jeff wrote:
Sun Dec 25, 2022 3:14 pm
Can you share the image ?
Sure! Here it is:
http://www.mediafire.com/?721ny04gmldnjsz

Tab.scp is the original, TabFix.scp has been fixed at the cell level in HxC to remove errors from 3 sectors and resaved in scp format.

What immediately catches the eye is that the resaved TabFix.scp has almost no red marks indicating non-flux areas. The tracks in TabFix.scp are also a bit shorter than the originals, resulting in slightly higher rpm. Nonformatted tracks, on the other hand, contain vastly less pulses, and these missing pulses are mostly responsible for the file size reduction.

All of the above seems to indicate that when an image is exported back to a scp many non-flux areas get stripped out, causing a contraction of the file size. Or, at least, this is my guess :)

Best regards,
radiorama.

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