Problem - Saved JPG File Sizes

[FrankB]

I have 17 large files in .TIF and .PSD format (22 to 280 MB) – all scanned images. I have no problem cropping, resizing, and saving as .JPG (642 x about 428 pixels) using PSE 6. Twelve of the .JPG images range in size from 66 to 104 KB, and the other five are 858 to 915 KB. When I check the final .JPG file size, each has the desired number of pixels. What can cause the file size discrepancies? Does a 900 KB .JPG contain more information than a 90 KB image? How can I get 66 to 105 KB .JPGs from each original? (I believe my technique is the same for all images. I have repeated my process with the same results.)

[dj_paige]

JPG involves compression. At the time you go to save the result as a .jpg, you are asked what quality level you want to choose. THe higher the quality level number you choose, the bigger the file (and of course, the higher the quality).

Further, two photos, with identical pixel sizes, saved at the exact same .jpg quality level, will have different sizes depending on the content of the photo (very complex photos, like lots of tree branches in front of an ornate building, will take a lot more space than a simple photo, like a beach and water and blue sky).

[TonyW]

Hi Frank and welcome to the forum. That does sound like rather a big difference but it is normal for JPEGS to vary considerably in size. The reason is that JPEGS use compression based on the image content. (the JPEG quality slider controls the compression). I assume that the images you have downsized are destined for the web so you don't need to use a high quality so you may have it set too high. A JPEG of a blue sky will be very small because it contains no detail so can easily be compressed to a small file size. A JPEG of a detailed object on the other hand will be big if saved with low compression (high quality) because it preserves every little detail. Using the highest quality isn't needed and can be detrimental because it can save artifact detail that wasn't wasn't part of the original image.

Try using Save for Web on the images. You can then see exactly what the file size will be at different JPEG quality levels.

Tony

PS I see Paige got there first but we do agree :D

[FrankB]

Many thanks I knew that the file size varried considerably, but not by that much. Some of the small files seem to be about a complex (on a 19" monitor) as the larger files. As long as they do't contain more resolution, then I am satisifed. I will resave the files using quality 5 instead of 10. (Save As and Save for Web give essentially the same file sizes.) :)

My wife is a fine art photographer, and wants some of her images on the web.

[ricklepage]

Paige is correct about the JPEG compression scheme: two files, even ones seemingly close in composition, can have wildly different final file sizes due to a host of little things that we might not even see. The compression level can exacerbate this even more.

The important thing is that the final image looks satisfactory to you for your purposes; that's it.

One last note, people still recommend using Save As... as opposed to Save for Web..., although I'm not so sure that this is really as big an issue as it was in earlier versions of Elements/Photoshop.

Rick