Images in MobiPocket

[wallcraft]

Originally Posted by andym

2. convert jpegs etc to gif

The problem is that, although gif file sizes vary, the "typical" 64KB gif image from a full color illustration is about 320x320. The gif optimizers I have looked at reduce the file size (for a fixed image size) by reducing the quality of the image. So, why not instead use a format like jpeg which is designed for lossy compression in the first place?

This seems to be what MobiPocket concluded too. Their original approach to importing images larger that ~64KB was to first convert them to .gif and then reduce the number of pixels in the image until the gif was small enough to fit in ~64KB. In addition to small images (itself a loss of image fidelity), you could also get variable image sizes from the same original image size in pixels. MobiPocket's new approach is to leave jpegs in the jpeg format but (presumably) increase their compression without reducing the image size to get them to fit in ~64KB.

There are cases where gif might be superior, e.g. sharp-edged line art with a limited number of colors. These may already be smaller than 64KB, and if not reducing the size of the image may be the best lossy compression technique available.

I am embarrassed that I did not reference the Illustrations in mobipocket thread, particularly since I posted to it. However, its example ebook illustrates the problem. Most of the internal images are ink drawings and are less than 64KB in .png or .gif, but the cover image is a 110KB jpeg. Once again, mobigen without -jpeg produces a much smaller cover image.

[JSWolf]

Wallcraft, exactly what code did you put into the HTML file to get the large image?

[wallcraft]

The original image was a jpeg. The HTML was from the example posted in the Illustrations thread:

<p><IMG style="WIDTH: 375px; HEIGHT: 500px" hspace=0 
src="BdIm__1.jpg" align=baseline border=0></p>

The 375x500 size is only honored by MobiPocket (according to their documentation) if it reduces the size of the image. In this case it was originally 510x680, and so far as I can tell it is still 510x680 in the -jpeg case. Either this particular size syntax isn't recognized, or the Desktop Reader does not reduce image sizes.

I used the command

mobigen.exe file.html -c1 -s0 -jpeg

to produce the attached .prc files (one without -jpeg).

[JSWolf]

So if I was to make a PRC file with an image larger then the screen of say some PDA, what would happen to that image?

[wallcraft]

What the documentation says is:

When images are displayed in the HTML flow, if they are too big to fit the screen (which is usually the case with photos or diagrams for examples), they are automatically resized to fit the PDA screen.

This is the case with the Windows Reader, but I don't have a PDA to test other versions of the software.

[JSWolf]

What you could try however is resize the desktop window and see if it resizes.

[wallcraft]

Originally Posted by JSWolf

What you could try however is resize the desktop window and see if it resizes.

It does.

[JSWolf]

Nice! Now what I need to do is figure out how to do this so I'll get a nice PRC and a nice LRF (html2lrf) fromt he same HTML file.