Focusing using JPG compression

[Grant]

I was talking to my girlfriend dad the other day, he works in optics and I was saying how I sometimes struggle with focusing. I was telling him how DLSR focus was making this much easier and he said, one possible way of focusing is to take a jpg image and compare the file size of the resulting jpg file. Because of the way jpgs are compressed, a slightly blurred, out of focus image should be smaller than a perfectly focused image...

I've been accepted to the Canons developers network so I can now do stuff with canon cameras (much like dslr focus does) so I'm thinking of making a little program that takes exposures every X seconds and compares the file size, when its at its largest point your in focus....

Before I start building, are there any flaws to this logic?

Cheers,

Grant

[FLO]

... one possible way of focusing is to take a jpg image and compare the file size of the resulting jpg file. Because of the way jpgs are compressed, a slightly blurred, out of focus image should be smaller than a perfectly focused image...

That's how Nikon's BSS (Best Shot Selector) feature works. A sharp pic will have more detail so does not compress as well as a fuzzy pic. The photographer keeps his finger on the button to take a number of pix which are stored in a buffer where their jpeg file sizes are compared. The largest wins and is saved to the memory card - the rest are discarded.

[Grant]

Steve, did we talk about this the other day? If so, it may have been you that inspired this, not my girlfriends dad... I'm soooo confused

[Jamie]

Go for it Grant.

We i need something like that..

[FLO]

Steve, did we talk about this the other day?

Yes

[Grant]

Steve, did we talk about this the other day?

Yes

Sorry mate, I had talked to Karens dad about something similar!

I'll get building it then