I will be showing you how to do it and I will show you real life examples I did so you can compare visual quality for yourself.
I use this process with all the pictures in my Instructables. The only ones I did not fully optimize are the three 1024x768 resolution DSC_0388_COMPx.jpg files I uploaded with different JPEG compression ratios, 90, 80 and 70, so you could see if it made a noticeable difference visually even though it did shrink the file size. The results can be seen in the table.
This instructable is not very technical and is not meant for professionals or graphic experts but for the ordinary joe (or joey) that wants to shrink some large pictures quickly without having to go to collage to learn how to do so.
Step 1: Getting the Program
You will need to download the program IRFANVIEW
"IrfanView is a very fast, small, compact and innovative FREEWARE (for non-commercial use) graphic viewer for Windows 9x, ME, NT, 2000, XP, 2003 , 2008, Vista, Windows 7".
After you have installed it, following the instructions, you are ready to start "shrinking" pictures.
NOTE: I am in no way affiliated with Irfanview. I earn no commission, kick backs, recognition or any other compensation from Irfanview for this instructable. I have worked with Irfanview for years and just love the program for its features, small size and simplicity.
Step 2: Cropping the Picture
The way to do this in Irfanview is to click somewhere on the picture and drag a rectangle around the part you want to keep. The rectangle can be adjusted after it is drawn so do not worry to much to be exact.
On the top menu click EDIT then CROP SELECTION or just press CTRL + Y
You should now only see the piece you wanted to keep.
Step 3: Resizing the Picture
I find the 1024 x 768 setting to be a good all round choice for most things but play around and decide for yourself.
Step 4: The Compression Ratio
Step 5: Test Results
The file DSC_0388_COMP1.JPG is at 1024x768 resolution with a 90 compression setting and delivers a 141 kb file size.
The file DSC_0388_COMP2.JPG is at 1024x768 resolution with a 80 compression setting and delivers a 113 kb file size.
The file DSC_0388_COMP1.JPG is at 1024x768 resolution with a 70 compression setting and delivers a 102 kb file size.
Look at the files and see if you can noticeably spot the difference.
Some have suggested that you can shrink file size even more if you reduce the amount of colours the picture uses, but I found, strangely enough, that the file sizes actually increased, so do not do that. The sizes you get with this method are small enough.
If you have a lot of picture you want to "shrink", Irfanview has a batch mode that can do 1000s of pictures in a few minutes.
To access the batch mode go to FILE then BATCH CONVERTION/RENAME and make your choices.
Now you know why I R FAN of Irfanview.