Mac Version: Help Understanding JPEG File Sizes

KR
Posted By
Kelvin_Ritchie
Jul 19, 2004
Views
234
Replies
3
Status
Closed
Hello,
I post to a RC model airplane forum and often I attach photos. They have a file size limit of 100k. Up until lately I took my photos in 640×480 and medium quality on my digicam but lately I’ve been taking them at 2m and 3m and superfine quality so the file sizes are often over 1m in size.

I’ll duplicate the photos and resize to 640 x 480. Then I’ll "Save As" the photo in PSE using JPEG and I’ll adjust the quality slider such that the preview states around 90k since it’s only and estimate.

However when I look at the file in the folder using the list option to display the files the file size shows a value higher such as 145k.

I’m confused. The file size in the Save As JPEG dialog is smaller. Is that the compressed size and the Finder file size is the uncompressed size. Then there is the information in PSE, the document size in the Status area of the photo window, it’ll state a figure such like 900k.

Can someone explain this to me so I can look at a file size in the Finder folder listing and determine whether I need to optimize it more to be under that 100k limit.

Thanks for any help.

Kelvin
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SS
Susan_S.
Jul 19, 2004
Using save for web seems to give me a file size in the finder closer to that indicated in the save dialog box. I’m not sure why the saved size is bigger using save as. My guess is that it’s things like ICC profiles and other extra data (EXIF and other metadata) that get saved with a file that increases its size above the image information – save for web strips all the extra stuff off. The PSE figure of 900k or so would indeed be the uncompressed file size.
Susan S
JH
Joe_Henry1000
Jul 19, 2004
Kevin,

After you save do you get a thumbnail of the image as it’s icon? I know that when PSE adds the thumbnail icon it increases the file size by quite a bit.

I also post to a forum (photozo <http://www.photozo.com/forum/portal.php>)that has the exact same size limit as the one you’re posting to. Here’s what I do:
Image>Resize….I enter 640 in the long dimension and let PSE constrain the other dimension. I then Filter>Sharpen>Unsharp Mask with settings of Amount=400%, Radius=0.2 pixels, Threshold=1 levels, to bring back some detail. I then Save for Web, adjusting the quality slider until I get in 100k range.

This work flow (I think I actually got the instructions from the photozo site) works pretty well and seems to produce images that are sized correctly.

HTH,

Joe
KR
Kelvin_Ritchie
Jul 19, 2004
Thanks for everyone’s reponses. I see a thumbnail in the Finder folder so I guess it’s all the overhead adding to the file. I like to keep the thumbnail because it helps pick out a photo faster. I found that using "Save for Web" the thumbnail wasn’t present in the Finder folder. So it appears the the the quality slider is at least close to being accurate. I’ll set to 90k to give some lee way. I’ll try the Filter settings first.

I haven’t played with the Batch feature yet. Can it convert a folder of photos so that each photo is 640×480 or close to that size and then optimise all to be close to 90k?

Kelvin

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