Expert: Kevin Stohlmeyer - 6/23/2010

Question
Hi Kevin,

When I open a 3.8MB JPEG photo in photoshop CS4, the file becomes 28.8M. Why is this?

I checked the resolution under Image>Image Size and found that it's 72pxi. I read your other answer about resolution and was wondering if there's anyway to fix this so that I don't have to change the resolution for every image.

Also, when I'm ready to print, which extension and what size should I save the pictures under if I want to send it to a photolab?

Thanks for your time,

Answer
Hi Trang,

Jpeg are a compressed file format, which means when saved your 28.8MB file turns into a 3.8MB file. The problem with this is this format is a lossy format, it will eventually degrade if you keep saving as a Jpeg over and over. If you are working on a file, save out as a .psd until you are finished. Then you can resave the final as a jpeg if needed.

Most digital camera files will come in as 72 dpi at a very large w x h. You will have to change the resolution on every image, but you can automate this using an action. Open a document that is 72 dpi. Then open the actions panel (window>actions) and click the new action icon at the bottom of the panel. Name your action (72 to 300 dpi) and click the record button at the bottom of the panel.

Next, go to Image>Image Size and uncheck "Resample Image" at the bottom of the window. Then change your resolution to 300 dpi and hit ok. Then click the stop button in the actions panel.

You now have created an automated action that you can use on multiple files by going to File>Automate>Batch. This will allow you to run this action on large numbers of files at one time.

Thanks

Kevin