Page 73 - DCAP303_MULTIMEDIA_SYSTEMS

Unit 4: Image

notes

Select an image to convert it from GIF format to JPEG format.

4.10.1 Cross-platform problems in Current scenario
With existing formats, there are substantial cross-platform differences with image viewing. The
images will be displayed, sure, but what people see will be very different.
For example, create a graphic on a Mac, say, and balance it to look just right this picture of
two children (See Figure 4.22). In which trouble is, it will look dark and contrasty on a PC,
because the default gamma correction is different from that on a Mac. On an SGI workstation,
however, it will look pale and washed-out because there the gamma is different again.
figure 4.22: Cross-platform Differences with image viewing

simple image on a pC on an sGi
The problem is that your browser has no idea where the image was created or how it was originally
displayed, so it cannot compensate for these differences. What is needed is for the authoring tools
to include this information, which is readily available to them. But existing image formats have
no way of storing this information.
How pnG helps

The PNG stores the gamma value used by the source platform which created the image, in a
standard place in the file which browsers, image viewers and authoring tools know how to read
and adjust for. So the gross lightness and contrast differences we have just seen are compensated
for automatically, without the image designer or the reader having to make any adjustments
themselves. (See Figure 4.23)

figure 4.23: not identical, but a Lot Better

on a pC on a Mac on an sGi

LoveLy professionaL University 67