Welles

robt,

What specific data are you looking at in the Information bar? Scratch Sizes, Document Sizes? Bringing a 10mb RAW file into PS translates to a 25mb file PS easily (in fact that seems on the small side) but to get a 1gb file out of that you need to be increasing the image size dramatically and adding a zillion layers, I'd think. Can you tell us more info about a typical file (pixel size, layers, bit depth etc) and we can tell you what you are seeing.

lenny109,

Serious users of PS have always had to push the limits of technological advance. Five years ago a 40gb hard drive was large, 10 to 20 gb pretty normal. We were using PS5.5 (I think). Maybe PS 6 was on the horizon. Very few people worked wit files which were 1gb or better. A gigabyte of RAM was huge. At the time a 100mb file was pretty large.

In a single layer image the document size is read by PS as the pixel dimensions times the bit depth. So if you are working with an 8 bit file you multiply the pixel width x pixel height x 24. If you are working with 16 bit files you multiply by 48. Divide that figure by 1024 and you get the approximate file size of a flattened image.However there is some PSD overhead added to create a file so the number above isn't a precise figure for the file size that Explorer or Get Info is reporting.

When you are working on a file the working file size reflects every layer, channel, History state (all those Undos add up big time), snapshots, etc. Photoshop can basically use all the memory you can throw at it and then a dedicated scratch disk, not your boot disk, is advisable for keeping the program happily humming along.

Sark

lenny109

What is important to understand is, that a file that is saved as a jpeg is smaller than the same file saved as a psd file, but when you open that jpeg in Photoshop it reverts back to a psd file.

All open files in Photoshop are basically psd's. If you don't resave as a jpeg you won't gain much in file size, even though you have previously compressed the file by saving in the jpeg format.

Sark

Welles

However, If you do resave as a JPEG you are losing data on every resave. Your best bet is to save as a TIFF (with layers and channels if needed) and use either LZW or ZIP compression. Your net file size will be about 1/2 - 3/5's of the native PSD format and still contain all the same data.

Sark

What confuses some people, is the difference between an open image and an image file. A jpeg may be 2mb stored as an image file, but when it is an open image displayed on your screen, even displayed in a browser, its size increases considerably.

You can test this by opening a jpeg with Task Manager open, and watching how much the Memory usage jumps. On my system a 2mb jpeg uses about 20mb of Ram when opened in a browser and 26mb opened in Photoshop.

For a single layer image, and assuming the Photoshop colour mode is consistent. Image size, in pixels, determines memory usage when a file is open in Photoshop.

If you open an image in Photoshop, and save it as a psd and, as a jpeg. When both files are re-opened in Photoshop, they will be the same size.

If you now save them both as psd?s, the jpeg version will be only slightly smaller (due to the image being less complex, caused by the earlier jpeg compression). When a psd file is saved, the complexity of the image has an effect on stored file size.

Also, if you were to save the jpeg version as a jpeg again, the image would become even less complex, losing more and more information every time it was opened and saved as a jpeg. Hence, the reason this should be avoided.

As Welles suggests, if you?re going to work on a jpeg image over a number of sessions in Photoshop, save it as a psd (or layered tiff) each time. When you?re finished editing, only then should you save back to jpeg.

Sark

Welles

Nicely explained, Sark! [righton]