| From: | Oliver Roberts |
| Date: | 26 Sep 2001 at 22:26:16 |
| Subject: | Re: [amigactive] Re: JPEGTMP ???????? |
Hi Andrew,
On 26-Sep-01 22:09:49 BST, Andrew Crowe wrote:
>> > Andrew Crowe :
>> >Assign JPEGTMP: T:
>>
>> A not too smart thing to do, as you may run out of memory that way.
> Unlikely unless you have only 8 or less megs, after all, IIRC it is only
The whole idea of JPEGTMP is that it is used as temporary storage for
when there is not enough real memory to decode the image completely.
So, if you're running low on memory, the JPEG decoder will use disk buffers
to swap data into and out of real memory (much like virtual memory really).
> used to hold decoded jpeg information temporarally until it is moved from
> the location on disk into memory, so it ends up in RAM anyway.
True, but only small chunks at a time - once it's finished with one chunk,
the JPEG decoder removes it from memory and loads another from disk. The
classic case which triggers JPEGTMP to be used is with large progressive
JPEGs. With normal JPEGs, the JPEG decoder only needs to hold data in
memory for a few lines at a time and can be thrown away after those lines
have been decoded, whereas with progressive JPEGs the data (image and
decoder data) has to be kept until the image has been completely decoded,
which requires much more memory. So, using temporary disk storage to
buffer this data allows you to decode images you otherwise wouldn't be
able to if disk storage was disabled and/or you ran out of memory (which
assigning JPEGTMP: to somewhere on the ram disk will make more likely).
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