Sent by Felix Miata on 10 August 2009 21:09
On 2009/08/10 12:20 (GMT-0700) Michael Stevens composed:
> Sent: Monday, August 10, 2009 11:35 AM
>>> It think it's still best to optimize your images for 72dpi - 96 max -
>>> because higher DPI images create larger file sizes, which make your
>>> web pages larger file sizes, which make them longer to download.
>> Image resolution has nothing to do with it's pixel size. For the web
>> the only thing you have to worry about are the pixel dimensions. An
>> 800x600 pixel image is going to display EXACTLY the same whether it is
>> 72 dpi or 600 dpi.
> I don't know what you mean by "exactly", but on a 72 DPI display any given
> image will be exactly 4 times the size (twice as tall and twice as wide,
> width times height) of that exact same image on a 144 DPI display if
> rendered at its native pixel size.
> No, it won't. If you display an 800x600 pixel image on ANY screen it will
> take up EXACTLY 800x600 pixels. The fact that one screen is 800x600 and the
> other is 1280x1024 means nothing. It may appear larger or smaller because of
> the different monitor resolutions but it's not. It will always be 800x600
> We are talking about displays here. While it's a number that you can
> calculate DPI/PPI mean nothing to a monitor. They are measured in total
> pixels. My screen is 1920x1200 and 24". Does that mean that a 22" monitor at
> 1920x1200 is a better monitor? No.
Think that if you want, but because the pixel density is higher on the
smaller, those with adequate vision may in fact find the smaller to be the
better when both render a particular object at the same _physical_ size. The
prime example is text, where jaggies are a common reader objection to screen
Your 24" 1920x1200 is about 94.3 DPI, while the 22" 1920x1200 is 102.9,
roughly "9%" higher nominally. On yours a true 12pt character box would be
about 15.72px tall by about 7.86px wide, for a total available pixel count
for each character of 123.56. On the smaller display 12pt would be about
17.15px tall by about 8.575px wide, for a total available pixel count of
147.06, or 19% more. That 19% can easily translate into less jaggies and
smoother curves and diagonals, and definitely does as DPI is increased
further than that small 9% nominal difference between your 24" and a 22".
> It has the same number of pixels in a
> smaller amount of space: smaller pixels. Both can only display 1920x1200
> pixels at a time.
> DPI is really only applicable when talking about the print medium where it
> really means something.
DPI most definitely matters WRT to physical size. Visit any store where
several laptops sit side by side on display. You should be able to find a 14"
or 14.1" sitting next to a 15.4", both at 1280x800 resolution. Because the
smaller screen has less area for its pixels to fit into, its DPI (~108) is
higher (vs. ~98), and, all else being equal, every image on it matching the
same image on the larger screen will be a smaller physical _size_.
Normal people measure physical size using some kind of dimension that other
people can relate to, and physical size is what my previous post refers to.
Pixels are not intrinsically one of those dimensions. It is only after a
pixel is converted to some other unit that its _size_ can be communicated to
someone else using mere words. WRT computer display screens it is common to
make that conversion as a statement of either dots or pixels per inch, but
commonly the term DPI is actually used whether dots or pixels are actually
If you put a 72px wide by 72px tall image on a web page and display it on a
72 DPI screen, it will measure one inch tall by one inch wide. Put that same
image on a 144 DPI screen and it will measure 1/2 inch wide by 1/2 inch tall,
which is exactly 1/4 the SIZE of that same image on the 72 DPI screen.
In CSS the term "size", as in "font-size", is only directly relative to CSS,
not physical size. 'Font-size: 75%' doesn't make text 75% of the parent size,
but rather 75% of the parent fonts-size's height. .75^2 is the effect of such
a CSS rule's so-called size, or 56.25% of the parent font's physical size.
The reality is those who set font-size: 76% on body are in fact setting a
page's starting text size to a mere 57.76%, not a whole lot more than half
the size, of whatever the user's ostensible preference happens to be.
How much better to get wisdom than gold, to choose
understanding rather than silver. Proverbs 16:16 NKJV
Team OS/2 ** Reg. Linux User #211409
Felix Miata *** http://fm.no-ip.com/
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