[Leica] that pesky megapixels and megabytes conundrum for the Yearbook

[hopsternew at gmail.com (Geoff Hopkinson)]

As the first contributions arrive for our Yearbook it appears that there is
some confusion on the specifications for the image files that people are
sending. Don't panic! Everything sent is in our book.

It might be worth revisiting some concepts for clarity and everyone's
convenience.
Here is an example.
An image file  6000 pixels x 4000 pixels has a total pixel count of 24 000
000. That is 24 million pixels or megapixels.
The resolution (number of pixels per inch) only affects the physical
dimensions of a print or on a computer screen. In the case of the LUG
Yearbook 3000 pixels would print to be 10 inches wide if the page was large
enough.

Assuming the same pixel dimensions the file size in megabytes (millions of
bytes) can vary enormously. That is affected by how the image information
is stored and in what format. (raw file or JPEG for example).

Starting from a raw file from your camera or a TIFF format image perhaps
you can make a smaller version of the image in the JPEG format by varying
two things.
Resample the file to a lower number of pixels, for our example 6000 x 4000
pixels to 3000 x 2000 pixels (a 6mp image)
Change how much compression is used in the conversion. Higher compression
means more loss of original information but a smaller file in megabytes.

Files that are much too big in megabytes will not result in higher quality
reproduction. Blurb will just throw away that information basically. The
posted guidelines of files between one and two megabytes are meant to help
ensure sufficient information for quality when printed while controlling
the file sizes both for email transmission and the overall book file size
as it has to be uploaded by me of course. Files larger than necessary get
shrunk by Blurb prior to transmission when the whole book file is uploaded.
That file can get very large.There is no user control over that shrinking.

The Blurb software does several things with image files put on the page.
By my choice as the compiler your images are not cropped nor expanded to
fit the whole space. The only loss of any part of the image is where the
full bleed option is used on the left hand page. That means that there is a
small overlap of unprintable pixels at the edges to ensure that the
printing goes right to the edge of the paper.

When your image is not the same proportions as the page 'frame' they are
being put into the longest dimension in pixels gets downsampled to the
maximum number of pixels of the longest side of that page fame. That
usually means that there is some unused area within the frame. You can
choose to crop your images anyway you want of course. Some people may want
to crop to match the exact proportions of the offered Blurb frames and/or
downsample their image so that the long dimension in pixels matches that of
the long dimension of the frame.

Clear as mud?????



Cheers
Geoff
http://www.pbase.com/hoppyman