image size

Image size is quantified in pixels. The image size for web pages should not exceed the display possibility.

Usually, a personal computer monitor uses displays ranging from 800 x 600 pixels to 1024 x 768 pixels.  Other displays can be used but are very uncommon.  Images on a web page do usually not exceed 2/3 of the page’s size.  It follows that the maximal image size that can be used for web publishing is 600 x 300 pixels.

Any image with a larger size will take more time to load on the navigator and will take more place on the server without an improvement in quality. Always keep images as simple and small as possible.

As a rule for internet publishing, do not use images larger than 20-30K unless absolutely necessary or those wider than 600 pixels or higher than 300 pixels. Better yet are those images 160 to 300 pixels wide and 100 to 200 pixels high.

Figure 5a. JPEG image of laser photocoagulation ; image matrix 180 x 152 pixels : quality 100% ; size 10.72k ; load time 3 sec at 28 8kbps (kilobytes per second ). This is a good exemple of image for web publishing.

Figure 5b. Bmp uncompressed image

Bmp uncompressed image, 8bits grayscale color, 1000*997 pixels, size 917k, load time 286 sec at 28.8 kbps. This image has a too large matrix for the web as only 500*467 pixels can be displayed. The image size is huge 860k it will take more time to load on the navigator (269 sec) and will take more place on the server thus without looking better. This image is Therefore not adapted for web publishing, because of its high size.  See below the same image in JEPG with a 500*476 matrix.

	467pixels
----------------------------------------------500 pixels------------------------------------------

Figure 5c. Same image as above but compressed as JEPG with 80% quality 0% smoothing and an image matrix of 500*476 pixels, 24bits color. The size is reduced to 32.93k; load time is reduced to 10 sec at 28.8 kbps. Moreover this image has the same quality as that above. This image is adapted for web publishing. However the 500*467 pixels take almost all available place on the page, image matrix could be reduced to 250*233. See below the same image in JEPG with a 250*233 matrix.

	233pixels
--------------------250 pixels------------------

Figure 5d. Same image as above but compressed as JEPG with 80% quality 0% smoothing and an image matrix of 250*233 pixels, 24bits color. The size is reduced to 12.4k; load time is reduced to 3 sec at 28.8 kbps. This image is adapted for web publishing. The 250*233 pixels don’t take all available place on the page. Could image matrix be reduced to 125*117 pixels ? As 250*233 are displayed this would reduce image quality. See below the same image in JEPG with a 125*117 matrix.

	233pixels
---------------------250 pixels-----------------

Figure 5e. Same image as above but with a reduced image matrix of 125*117 pixels. The size is reduced to 6.2k; load time is reduced to 1 sec at 28.8 kbps. However this image is not adapted for web publishing, because of its low quality. What happens: as 250*233 pixels are displayed the low size matrix of 125*117 pixels reduces image quality.