Originally written and owned by Carol Spears
You can make your jpegs smaller without changing the pixel width of the image. Actually you can change the weight of the image a lot. I used an(other) image from APOD. The original image is huge (3000 pixels wide) so I also made a smaller (pixel width) image available. To prepare this image for the web, you should first reduce the image to a better width and height for web viewing as described in the scale quickie. Right click on the properly scaled image and follow the menus<Image> File -> Save As…. The Save Dialog will pop up.
I generally type the filename I want into the text box, but the Extension drop menu can tell you the available file formats (depending on the libraries you have installed and the conditions of the image you are trying to save). If GIMP complains right now, or if “JPEG” is grayed out in the Extensions menu you should just cancel out of everything and step through theChange the Mode Quickie.
In the JPEG Save Dialog, you can opt for GIMP defaults which reduce the size quite a bit, without hurting the visual quality in a way that I can detect. This would be the safest and quickest thing to do.
If you would like to make it smaller still, make sure that the “Preview” toggle is on and then watch the image area and change the compression level by moving the “Quality” slider down. You can see the quality of the image changing, especially towards the leftmost end of the slider. Here is a screenshot of me doing this very thing. As you can see, very small is also very bad. I have a screenshot of me setting the Quality slider to a more acceptable level here.
I have not been showing the actual jpegs I created so that we could end this quickie with a race. Clicking this page should “race” these jpegs to a web page (the first time you see an image in most browsers, you are also waiting for it to write to the cache, so the first time is the worst). With my cable modem, I was unable to see a difference in the load time, but the difference in what you actually see is fairly interesting.