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Multimedia | Scanning Tips | Presentation
Tips
Your
first consideration:
The
resolution of the presentation laptop or projector
Data projectors are generally 800x600 pixel devices, some are now 1024x768,
earlier models were only 640x480 - you need to know.
If it's for a laptop display the same applies - if you're not sure then
'right-click' on the desktop, select [properties], [settings] and see
what it says about screen area.
While
you're there make sure that 'colours' is set to 'high color (16 bit)'
Your
second consideration:
How
much of the screen is this image going to occupy
Why
is this important?
The
computer can only display as many pixels as the resolution supports -
if your scan is any bigger than this it will contain data that does not
display. This will make the file size larger and slow down the presentation
for NO visual improvement!
Conversely an image that is smaller than you wish to display will 'pixelate'
(more than one pixel of your display will be used for each pixel of the
image giving a blocky appearance)
Assuming an 800x600 display: no image should have a final size greater
than either 800 pixels wide or 600 pixels high. A logo that will be placed
at the bottom of a slide may only need to be 150 pixels wide. Bear all
this in mind before you start...
Scanning
Now
you know what size image you need (approximately) you can start scanning.
Your initial scan should be around 4x larger than the final image - generally
'the bigger the better'
Why?
This
gives you some extra data to play with... When you optimise the image
(particularly when getting rid of blemishes, scratches etc) the additional
pixels allow much more subtle editing.
The
image is in Photoshop - what now?
1.
Throw away anything you don't need - use the crop tool to trim any excess
area that you scanned
2. Levels: sort out the light and dark. This is normally the single biggest
improvement to any image.
Try 'autolevels' first (under Image, Adjust, Auto Levels, or Shift+Ctrl+L)
If you don't like the result click Edit, Undo or Ctrl+Z and then do it
by hand
Go to Image, Adjust, Levels, or Ctrl+L and move the three little sliders
around under the histogram. This is a purely subjective operation but
generally you want the blacks black, the whites white and then shift the
bit in the middle until it's as good as it gets...
3. Colour balance: if the colours need general adjustment (particularly
when you're scanning transparencies) select Image, Adjust, Colour Balance,
or Ctrl+B and add or subtract until it looks better
4. Dust and scratches: sort these out using a combination of the rubber
stamp tool and the dust and scratches filter. Rubber stamp to copy good
areas over bad and the filter for areas without great detail (sky, solid
colour etc)
It
looks pretty good - what next?
1.
Size: it IS important. Now resize your image to its final size (under
Image, Image Size) which you determined earlier - make sure that 'Constrain
proportions' is on and that dimensions are in pixels
2. View the image at 100% magnification - are you happy with it?
Happy?
Go to Saving
Unhappy?
Start
again from scratch - either re-scan or undo your edits back to the original
(use Alt+Ctrl+Z) or go to the history window and step backwards
It's
OK but...
Here's
some more options
1. You can further tweak the levels, colour balance and maybe look at
the brightness/contrast option under Image, Adjust
2. Try sharpening the image (Filter, Sharpen, Sharpen) - this almost always
helps
3. Occasionally a slight softening of the image can help (Filter, Blur
and then try a few options)
Saving
Once
you're happy with your image it's time to save - but what format?
Photoshop can save many different file types and PowerPoint can import
most of them - how do you choose?
Your only considerations are size and speed.
File size is determined by the number of pixels, whether or not the file
format uses any form of compression and the amount of information stored
for each pixel.
1. You've already sorted out the required number of pixels.
2. BMP file types apply no compression and are consequently relatively
large. However since there is no compression, no time for decompression
is required. BMP supports 24bit and 8bit colour depth - more on this later...
GIF and JPG files types both compress the file size but in different ways.
JPG compresses a file by throwing away information and you can select
the degree of 'lossy' compression to apply. This makes the saved file
considerably smaller but you need to be careful that you don't over compress
and lose image quality. You also need to be aware with JPG that any subsequent
save of the image will throw away more data and further degrade the image.
GIF is a non-lossy compression but only supports a colour depth of 256
colours (or 8bit)
3. The amount of information stored;
When you scan an image the basic format allows each pixel to be any of
millions of colours (24bit) and this facility results in the truest reproduction
of an image - it also requires a lot of data to be stored in the file.
Files of this type can be saved as BMP or JPG.
Alternatively you can reduce the amount of data stored to just
256 potential colours per pixel
(do this with Image, Mode, Indexed colour - the options chosen should
be Adaptive palette, 8bits/pixel, Diffusion dither). This works best on
images that do not contain a great range of colour to begin with and is
at its worst with any sort of graduation - experiment and simply undo
the operation if you don't like the result. These images should be saved
as BMP (selecting the 8bit option) or GIF.
This document is brief outline of the areas covered in a half day training
course designed to let any competent PC user get the best out of scanning
images via Photoshop v5 for use in a Powerpoint screen show. [top]
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