Next message: Leonard Rosenthol: "RE: [WinMac] Re: Rule of thumb"
Leonard,
Go back to the November 1995 (?Nov. 1994?) MacWorld magazine issue for an
excellent cover story description on the how's & why's of Photoshop memory
management.
In a nutshell, as long as the uncompressed image - And the first Undo - is in
RAM, then you don't have to hit the scratch disk at all. Virtual memory
management - No matter how sophisticated! - only comes into play when you run
out of free RAM on the Mac. As you drop from 3x down to 2.5x in free RAM, the
speed drops off slightly.
As you drop off from 2.5x down to 2.2x free RAM for the image, the speed
starts to drop off even more. As you get down below 2.2x, Photoshop's VM starts
to kick in, causing the scratch disk to be "hit" more and more; slowing down
operations to a (relative) crawl.
Image rotations require even more free RAM to execute totally in RAM: If you
have a 100 x 100 pixel image, and you rotate it 45 degrees, the new image grows
to 142 x 142 pixels in size. Note that a 45 degree (or multiple orthogonals of
45 degree) rotation will cause the image to expand the most, with concomitant
increase in RAM needs.
Happy New Year!
Dan
>-----Original Message-----
>From: Leonard Rosenthol [mailto:leonardr@lazerware.com]
>Sent: Friday, December 29, 2000 2:41 PM
>To: winmac@iffy.com
>Subject: [WinMac] Re: Rule of thumb
>
>
>At 1:16 PM -0500 12/29/00, Mark Workman wrote:
>>We use 350 pixel/inch CMYK images and the size in megs is pretty close to
>>half the size of the image in square inches. Makes for easy math.
>
> You could just use the actual numbers and do the math.
>
>Each pixel in an image is either 3 (RGB) or 4 (CMYK or RGB w/alpha)
>bytes in size. Multiple that times the number of columns (image
>width) and then that times the number of rows (image height).
>
>
>I missed Dan spouting drech again, didn't I...
>>Even using the 28 megabyte figure, that's 84 megabytes of free RAM
>>(installed RAM minus operating system minus Photoshop); which puts
>>what you need somewhere between 128 and 192 MB of installed RAM.
>>
> Dan seems to be forgetting that Photoshop does NOT
>NECESSARILY load an image entirely into RAM, it uses a VERY
>sophisticated virtual memory system of it's own to handle images.
>So any calculations involving images and Photoshop aren't guaranteed
>to be accurate. HOWEVER, I agree that more RAM is always better when
>working with Photoshop!
>
>
>Leonard
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