Download Times - Quality vs Speed
October 8, 2006 10:03 pm
Whether you are e-mailing a picture to a friend; posting art work to an online gallery; or writing an online tutorial, it is critical to form a balance between the quality of the image and how long it will take that image to download. In the above cases, bigger is usually not better.
If it takes too long for an image to open, it is a good possibility that the viewer will give up and not bother looking at it. With the advent of high speed internet access, many people have lost track of the size of their image when they post it. Even though I have high speed Internet, I usually pretend that all I have is a 56.6 kilobit per second modem when I am preparing images for the web.
The circled numbers above show the time it will take for the image to download. The screen on the right shows the settings I use for Photoshop. Everyone has their own preferences. Below is an enlarged version of download times and also quality settings. Of course, the resolution is screen resolution, 72 dpi. I have never timed the downloading of an image. I use the times more for reference numbers.
If I am posting an image in my gallery, I like to aim for a download time not greater than 7 seconds at 56.6 kbps. When I am posting images in a tutorial or review, other factors have to be considered. The images have to be clear and legible; thus, sometimes they are a little larger than I find desirable. I keep my images, for my personal web site, no larger that 450-500 pixels by a corresponding value. When I create images for an article, I sometimes have to extend that value to 600 pixels.
Can changing the pixel dimensions and resolution of an image be accomplished in most image editing programs? The answer is "yes." The only programs I have found that do not allow for this are the automatic ones which try to do all the work for you.
Although the versions of the programs below are not current, they still demonstrate that resampling is possible.
There are two ways available for approaching uploading images. If you are using a digital camera and NEVER plan to print the images, then take them at screen resolution and at approximately the correct size if that is possible. That way you will leave out most, if not all, of the intermediary steps. However, if you are going to use the image in different ways, then you want your image to have enough information in it to be able to create a print from it as well as to put it up in your gallery and use it in a tutorial, for example. The same theory applies to creating art work from a blank "canvas".
I took this image on a recent trip. Once I downloaded it into my computer from my digital camera, it was 22 MB uncompressed and about 3.5 compressed.
I changed it for the web in two stages. The first stage is pictured below. Make sure that Resample Image is always checked. These screen captures show how I perform this in Photoshop.
The second stage is also pictured below. Even though I am making the image smaller, I have still found that sharpening the image is a must. My article on sharpening, which I refer to below, discusses sharpening an image as you increase its size. The directions are the same when you want to make the image smaller. As an aside, I have read that smoothing an image is what is done when one is decreasing the size of an image. I have found that sharpening, using the unsharp mask, works better in most cases.
If you want more information on resolution see my article on resolution on my web site of PerpetualVisions. And for information on sharpening, see my article on sharpening which is also on my web site. Remember, bigger is not always better.
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The Paula Sanders Report is a regular Renderosity Front Page featured column, where Paula investigates and comments on graphic software, techniques, and other relevant material through her reviews, tutorials, and general articles.
October 9, 2006