What format was your 1MB original file? A PSD or a TIFF? Saving either of these as a maximum quality Jpeg will always result in a smaller file size.
That’s the whole point of the Jpeg. To make a final destination save, whether for web use, screen display, or to send away for printing, in a more compact form.
Chris the origanal was jpeg too, this is what I cant understand
Maderic: I take it the original was a jeg off a digital camera. If this was at a higher compression then it would be smaller than a resaved Jpeg at minimum compression. Also there is the small matter of the added metadata which Photoshop will have added to the file.
The real issue here though is that every time you save and reopen a Jpeg you lose quality. If you must shoot Jpegs (even on the Fine setting) you should always save them as TIFF or PSDs on your computer.
The Jpeg compression process "throws away" pixel data to achieve such small file sizes. Upon reopening them this has to be "reinvented" – and this will at best be a good guess. Subsequent saving and reopening will have less and less "real" pixel information resulting in a dramatic lowering of quality.
If the camera can save out images as Tiffs this is preferable to Jpeg. Better still – shoot RAW files as these will contain so much more information for you to work with.
Reserve Jpegs for holiday snaps, and only ever save files in the Jpeg format if you are certain they are never going to need to be edited or resized again. eg: for web use, for on-screen display or for printing (at the saved size).
I hope this has been of some use.
Chris.
Yeah brilliant thanks. One more thing though. When doing the final save to jpeg from for example a .tiff file should I set the value to maximum quality (12)??
Thanks
Hi maderic
1 take one of your images
2 use Save As and change the filename ever so slightly, say <filename>001 but save it as JPEG with resolution 1
3 close then open <filename>001 then save as <filename>012 at JPEG resolution 12 (or max, you may use other programs for this test)
4 compare file sizes and Hey! What’s going on?
Ans: IT, digital stuff are so closely interwoven with method as well as output. These are not independent events and are probably wholly dependent (using independence in a scientific and/or math sense)
Try the same Save As options using TIFF, PNG, JPEG2000 then compare quality of the output with filesize and method used.
You can do all of the above with Photoshop – great innint!
Each file extension JPEG, TIF, PNG uses a different compression algorithm which will of course affect image size as well as image quality
should I set the value to maximum quality (12)??
Depends upon the use to which the Jpeg is to be put.
If I’m saving a Jpeg for the web or for emailing, I’ll generally use a setting of 6 or 8. When sending 300 ppi images by FTP (or on disk) to my laboratory for printing, I will save them at maximum quality (12). But I always, without exception, keep a high quality master on file in TIFF format.
Chris.
maderic:
Maybe it helps to think of TIFFs DNGs RAW as the image manipulation side of things. It’s better/best to have as much data there as possible.
Once the tweaking and post processing corrections or creative improvements have been completed then save as TIFF, PSD (I prefer PSD – the balance of algorithms seem to work better for me).
Once the image is in a finished state use Save As to define filetype, image quality, influence filesize and these will (usually) IMHO relate to the use that the image will be put to.
Remember that just 10 years ago -really!- modem speeds were in the order of jumping from 14k to 28k to 36k to 56kbm. A 1 meg file at the slowest download speed would be a real turn off especially if there were a few on, say, a website homepage.
Dunno if this helps at all…
