[Xerte] Re: FW: jpgs degrading - is this a new phenomenon?

Mon Jan 16 10:24:43 GMT 2012

The best would be swf, but most people don't have vector images, or tools to make swfs. Vectors will scale with no loss of quality.
Then .png, which is a kind of hybrid vector / raster format, but performs pretty well.
After that the issues become more difficult: if you use a jpg or a gif, and allow the user any control over the final size, there are going to be issues.

From: xerte-bounces at lists.nottingham.ac.uk [mailto:xerte-bounces at lists.nottingham.ac.uk] On Behalf Of Alistair McNaught
Sent: 15 January 2012 08:29
To: Xerte discussion list
Subject: [Xerte] Re: FW: jpgs degrading - is this a new phenomenon?

Quick update
Thanks very much all for the further advice and help.

I might have confused things a bit by using table image examples - these weren't the actual images I was trying to get in the LO, I just knew that they would demonstrate the issue best.

For my own purposes it's reasonably simple to swap jpgs for gifs or pngs but I might need to look at adding some guidance for tutors on choosing the best image format and having different free tools to swap from one to the other as required. Whilst the basic gif v jpg guidance is straightforward enough to understand there are often images (like logos with graduated colour swatches) that don't neatly fall into one category or the other. Maybe 'if in doubt use png' is the best rule of thumb.

A

From: xerte-bounces at lists.nottingham.ac.uk [mailto:xerte-bounces at lists.nottingham.ac.uk] On Behalf Of Pat Lockley
Sent: 14 January 2012 21:04
To: Xerte discussion list
Subject: [Xerte] Re: FW: jpgs degrading - is this a new phenomenon?

I think you notice it on these pictures as JPEGs don't handle lines very well.

Usually the internet rule is when using text, use a GIF as gifs don't pixelate lines like a jpg does.

When given big blocks of colour, like on a photo, jpgs are fine
On Sat, Jan 14, 2012 at 8:37 PM, Ron Mitchell <ronm at mitchellmedia.co.uk<mailto:ronm at mitchellmedia.co.uk>> wrote:
Hi Alistair
This is all quite predictable and not a server or flash player issue - just a simple fact of viewing raster images at different to actual size. Your LO is set to full screen try switching to default so it's 800 x 600 and you'll see that some pages look better at that size and others look better at full screen?

It wouldn't help with all your images but for the example here what about using the Charts > Table page type e.g. http://itq.jisctechdis.ac.uk/xerte/play_85
HTH
Ron

From: xerte-bounces at lists.nottingham.ac.uk<mailto:xerte-bounces at lists.nottingham.ac.uk> [mailto:xerte-bounces at lists.nottingham.ac.uk<mailto:xerte-bounces at lists.nottingham.ac.uk>] On Behalf Of Alistair McNaught
Sent: 14 January 2012 17:45
To: Xerte discussion list
Subject: [Xerte] Re: FW: jpgs degrading - is this a new phenomenon?

A final version with 3 pairs of images (jpg v png) at  sizes 300, 360 and 550 respectively. In all cases jpgs show significant degradation. PNGs only show degradation at the 550 px point where they are being shrunk from 550 to 470 to fit the space.

In the short term I'll stop using jpegs in favour of pngs and gifs but in the long term I'd be really interested to know why jpegs fare so badly. They will be the format of choice for a lot of less technically inclined users so if it ispossible to determine whether the code has changed and if so to change it back I'd be very grateful.

That's all the excitement needed for one weekend - I'm signing out now!

All the best and thanks for the rapid responses Dave and Pat.

A

From: xerte-bounces at lists.nottingham.ac.uk<mailto:xerte-bounces at lists.nottingham.ac.uk> [mailto:xerte-bounces at lists.nottingham.ac.uk] On Behalf Of Pat Lockley
Sent: 14 January 2012 17:08
To: Xerte discussion list
Subject: [Xerte] Re: FW: jpgs degrading - is this a new phenomenon?

It looks like XOT is stretching them, and so is having to fill in bits (which is degradation via interpolation, which sounds redundant but lacking the words to find a better one - negative amelioration?)

The originals are fine.

What's the maximum size? 640 something?
On Sat, Jan 14, 2012 at 5:02 PM, Alistair McNaught <Alistair.McNaught at heacademy.ac.uk<mailto:Alistair.McNaught at heacademy.ac.uk>> wrote:
Hmmm - here's the test I did for Pat:
First 2 slides of http://itq.jisctechdis.ac.uk/xerte/play_82 show significant quality difference yet the image below shows they are virtually identical in their raw form.