Posted by seahunt on March 20, 2001 at 12:36:40:
Hey Folks,
I've been busy and both my ISP's are having problems, but I wrote
this up for somebody else, so I figured I would post it here as
well.
Enjoy the diving, seahunt
Image Prep for the Internet
It is easy to improve almost any scanned picture with Photoshop
by using:
1. Sharpen Filter
2. Image correct (levels) - either automatic or manually pull in
each end of the histogram just a bit.
3. Brightness if needed. (10 % of the time)
Now, some pictures need more than that, but for 90 percent
of the scans, that is plenty enough. Sometimes brightness must be
adjusted to benifit, but usually it is near correct to start
with.
Photoshop has a zillion controls, but really, most people
just want to improve pics. I played with it for a long time,
starting years ago. Just two simple fixes are are mostly
all that are needed for pics though.
Scanning
.JPG is the format developed by AOL for web images. It
is good because it is compressed, but it is bad because it doesn't
copy well (called lossy). JPG's are saved with different levels of
compression/lossiness, generally between 1 and 10. 10 is the least
compressed and has the most image information. 1 is the most
compressed and the image loses the most information. Level 3 is
about the most compression that can be used for a picture for the
web and still have it look good.
A good method is to scan a pic and save it as a bitmap (.bmp) or
a level 10 .JPG and then save a copy to be adjusted as a .jpg by a
similar name. That way the copied .bmp/.jpg can be manipulated,
enhanced, sized, sharpened and copied all you want, but the original
is never modified (except for an initial trim or rotation at scan
time). The copies are preped for viewing or posting.
There is a drawback to .bmp's in that they are very big, but
with a big hard drive or a CD Writer, that doesn't much matter.
Scan at 75 pixels per inch (ppi) at minimum, because this is the
size it will be displayed on a computer monitor. It is probably better
to scan at 300 ppi. The picture can always be adjusted to the size
needed, but detail is saved. Also, you want at least 300 ppi if you
intend to print the picture. Another reason to scan finer than 75 ppi
is because if you crop the picture, you can still make it the size you
want to use.
Image Manipulation
All of these effects must be experimented with. Many times you
will want to go to the Edit menu and select to Undo the last change
that you made. This is just how you experiment to see what effects
best enhance the picture.
1. Almost all scanned pictures can be improved by using the Sharpen
filter. Enlarge the picture to full size view so that you can see
the effect of the filter. Sharpen it. This is usually enough, but it
can make a photo grainy, especially if you have used the Sharpen
Edges filter. If the picture shows a graininess, use the Undo to
remove the filter or better yet, select to Fade Sharpness to a level
that looks good (say 50% to start).
2. Scanners do not scan colors perfectly. There are just naturally
some colors that don't scan well. Because this is well known, there
are ways to put back the colors that were not properly scanned.
Digital cameras should not have this problem.
Size the picture so that you can see the whole thing.
Under the Image menue selection, there are two level controls
you can use. Auto levels is easier and usually works well enough.
Sometimes though, it doesn't improve the picture quality though, so
use the Undo function and try the Levels function
Under the Image menue selection, select Levels. This shows a
Histogram of the image colors. That is a graphshowing how much of
each color range is in the picture. If you look at each end of the
graph, there is normally a small flat area at each end of the graph.
These areas represent information that do not help the image. You
want to use your mouse to pull in the pointers at the end of the
graph until they are just inside of the flat parts of the graph.
This should give you good color correction. Experiment and play with
it until you see what it will do for you. You may just want to go
back to the Auto Levels if you don't get what you want.
3. Under the Image menue selection, you can select Brightness. Again
play with it to see what it can do to help make your image more
visible. You can usually go up to 75% without it making your picture
look funny and it will show a lot that is hidden.
To get your scanned images to look their best, you have to play
around a bit to see what happens. It's not hard, especially with a
bit of a guide to start you along. There is a lot of other stuff
you can do, but that's for you to figure out. here are a couple of
other tips to think about.
Some images are harder to work with. In the picture on page
www.diver.net/seahunt/d_boiler.htm is a typical pic you take when
on a dive boat. The sun behind a guy in a black wetsuit, with a red
lobster in front of him. The lobster is dark and so becomes invisible
in front of the dark wetsuit with the hazy sun behind it. I had to
enlarge the image, outline the diver and the lobster and then up
their brilliance, amoung other things. I would love to know better
ways to enhance images like that, but that's the best I could do and
it shows the bug pretty good.
After you have the effects you want, there is always composition
to consider. What is in the picture that you want the viewer to see?
What could be left out? It is sort of like when you take a picture
of your friend. Most of the picture may not be your friend. There may
be lots of sky or a building or something else that you don't care
about or don't want in the picture. Use the Box Select tool to select
the area you want to show, then use Image / Crop function to remove
what is not wanted. Then you have your friend in the entire picture,
at a real good size. Always leave some fram around your subject though
or the image may look strange.
Scratches can be removed with the Blur tool, but do it carefully.
If you ever scan something from a magazine, art print or
newspaper, use the Descreen setting on your scanner S/W to remove
the pattern made by the printer. te Blur filter can do this as well.
The Sharpen filter will cause the printer pattern to show more.
Removing Red Eye is sorta tough with PhotoShop. I do think that
there is a better way, but this will work. Enlarge the picture so that
you can outline the area of the eye with red in it. Use Image / Color
Balance and move the red selection down until the red is gone. It works
OK, but there are other things you can play with that may work better.
There are a lot of effects that can be used here, but none of them
always do what you want. You still have to play around to get what you
want. If you want to give a person some really strange eye colors
though, that is fairly easy.
All of this is a description for using Adobe PhotoShop, but other
image prep software can do the same things, it's just done a little
differently with different names on the menu selections. Again, it's a
matter of playing around until you get what you want, so always save
the original unchanged.