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Photoshop and image sizes? Just wondering.

johnny99
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Last Modified: 2010-04-25
Hi,

I was just wondering: in PhotoShop 3.0, the preview box in the bottom left-hand corner shows my image sizes as twice what the finder says they are.

To be specific: 400 x 286 pixels x 3 channels: PhotoShop quite logically tells me I have a 400 x 286 x 3 / 1000 = 343K image. The finder tells me it's 170-odd.

Also the PhotoShop Bible tells me that the _second_ number in the box should be the same as the first, if there is only one layer. It isn't, it's slightly smaller: 315.

This isn't an actual problem, but I'm forever converting from RGB to indexed for the web and checking out the size, but the box is giving me weird information -- am I crazy, or what?

johnny99
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Commented:
You're not crazy - those numbers are *never* accurate in regard to the size the file will be when it's saved.  What's more, it's even worse for WWW formats.

When you save a GIF of JPEG, the file size is reduced algorithmically - and the precise degree of reduction depends on the actual content of the image.  (I've tried creating a "calculator" to no avail).

And so - the only answer to "how will I know" is  "experience" - after creating graphics for a while, you should get the "feel" for about how large a given image should be.

If you want to shoot for maximum optimization, I'd suggest using an automated tool: Debabelizer (if you can spare the cash) of GIF Wizard (http://www.gifwizard.com/) if you can't.

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Commented:
Thanks for reassuring me about my sanity at least -- what do you do?

Personally I just save, switch to the Finder, and look there: is that logical?

Or is the rule of thumb of roughly a half close enough?

My life is made harder at work by an NT server which tells Macs bizarre file sizes. Even the smallest GIF takes up over two gigabytes according to NT!


Commented:
Hiya...

There is also another factor to be considered, and thats the files size in the finder is dependant on the size of the drive. Especially for small files. this is because, due to the way disk space is allocated, If you have a big disc (2gig say), your smallest file size would be multiples of 64K. For a 300 meg disc the file size will be in multiples of 8K. This would mean that a 16K file on a small disk, would grow to occupy 128K once moved to your hard drive. This has become even more apparent to you because you are trying to get your files as small as poss for the net.

try this....
copy a floppy full to the brim with files of 8K to your hard drive. then copy them back to the same floppy, If you use a 1-2gig drive for this experiment, you will find that there is not enough room on the floppy to copy them back again.

regards
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