Screen Resolution

[lustyd]

Hi all, I have a PRS350 and a PRS650. These apparently have the same screen resolution, and seem to run the same software. If this was the case it would be reasonable to expect the zoom levels to show the same text on the same page. For some reason the 350 shows seveal lines fewer than the 650 at the same zoom and page settings.
Am I going mad or are they actually different?

[wallcraft]

Yes, they have the same resolution in pixels and yes there are fewer words per line.

There are two approaches to character size: pixels and inches (or points, which are usually 72 per inch). If the size was in pixels, the 350 would have smaller characters but the same number of words per line. The character size is actually in inches, so the 350 has more pixels and the same physical size per character - and therefore fewer words per line.

The Hanlin V5 (vs V3), for example, uses the pixels approach, which is probably easier from a software point of view.

[lustyd]

Originally Posted by wallcraft

Yes, they have the same resolution in pixels and yes there are fewer words per line.

There are two approaches to character size: pixels and inches (or points, which are usually 72 per inch). If the size was in pixels, the 350 would have smaller characters but the same number of words per line. The character size is actually in inches, so the 350 has more pixels and the same physical size per character - and therefore fewer words per line.

The Hanlin V5 (vs V3), for example, uses the pixels approach, which is probably easier from a software point of view.

Thanks wallcraft that makes sense, although I can't help but feel sorry for the developers! it hadn't occured to me that 12 point was a physical size rather than relative, I guess because Windows ignores the size of pixels

It gets rather interesting when you see all the ways in which HTML stylesheets can assign text sizes. Here are three:

Pixels:

Probably the most common sizing used among those who design web pages. Each device has a certain number of pixels per inch when it comes to CRT and LCD screens. EInk screens also specify a number of pixels per inch but eInk screens display text differently than a traditional LCD screen. The 350 has appx. 200 pixels per inch of screen both horizontally and vertically. So if you specified a font size that actually stands 20 pixels tall, the text would be 20/200 inches tall or 0.1 inches tall. A PC LCD monitor might have 96 pixels per inch, so the same 20 pixel tall text would stand 20/96 inches or 0.21 inches tall. So pixels can be of different sizes for different screens.

Points:

Probably the most common sizing used in the printing industry where printed books, brochures, etc. are produced. I think points are frequently considered to be 1/72nd of an inch or 72 points per inch. Using points the printing document designers could estimate rather accurately how much text would fit on a printed page. Although I don't recommend using points for eBook stylesheets, a lot of printing based publishers do because that is what they are used to.

EMs:

Instead of using a size per inch, EM is relative. In HTML if you set the standard text size to some amount, then EM represents a size in relation to the standard text size. Setting a size of 1.5em is the same as setting the text size to be 1.5 times (150%) bigger than the standard text size. For example, if you set the standard text size for your document to be 16px, then assigning a value 1.5em to a heading level 1 (H1 tag) will increase the text size for H1s to 24px. In theory, if you do not define the standard text size for a document, the device on which it is displayed will choose one that is optimum for that device. Thus using EMs to define all the headings and non-standard text sizes would make them relative/proportional to the device optimum. In reality that might not actually work out as well as you would like.

Bottomline:

HTML and eBooks are much like the "Life is like a box of chocolates" quote from Forrest Gump, you never know what you will encounter in the stylesheet. I've seen all three used within the same ePub! I personally prefer pixels because I used them so much with HTML in the years gone by. But to be honest, for ebook EMs is probably the more logical form of measurement but perhaps the most difficult to visualize.

[kartu]

Viewers on Sony use "dpi" parameter which differs from reader to reader, but is easy to change. Downside of changing it would be that EBL wouldn't be able to pre-format books for custom DPI values.