I am back with a short trip into the land of the non-square pixels. You can change the resolution and aspect ratio not only of the image but also of the individual pixels.
And then I have a reminder about animated GIFs – a “commercial” from SCALE 7x.
SCALE 7x, the premier Open Source Community conference in the southwestern United States, returns to the Westin LAX Hotel, site of the 6th Expo!
For 2009, the main weekend conference at SCALE 7x has been expanded. In addition to the three main tracks, a Beginner’s track and a Developer’s track have been added.
SCALE will be February 20th – 22nd, 2009.
The TOC:
00:40 Anamophic images
01:40 Making an image with non-square pixels
02:30 Changing the resolution and units
03:35 “Dot for Dot” has to switched off
05:10 Changing the unit of the rulers
06:00 Setting up the grid
08:20 Scale7x announcement
This work is licensed under a
Creative Commons Attribution-Share Alike 2.0 Germany License.
Tags: aspect ratio, dot for dot, pixel, scale
I was happily surprised to see you were covering nonsquare pixels here.
Some more exact info:
If you want exactly 2:1 pixels, for example, the image resolution must be (XD/2) * YD dpi where D is the monitor resolution seen by GIMP. I have set my ‘monitor resolution’ to 96×96 so that 48×96 produces 2:1 pixels and 96×48 produces 1:2 pixels. (96×96 is also fairly close to accurate measure of resolution for my monitor)
Otherwise, because image pixel size is not exactly divisible by screen pixel size, there can be an ugly ‘unevenness’ — some pixel columns can look more wide, thin, tall, or short than others.
Adjusting image ppi: the ‘Scale Image’ dialog offers this option; it’s pretty much the same as the one in the ‘new image’ dialog.
Converting between ppi:
For example, if you want to convert 2:1 pixels to 1:1 (square) pixels, use ‘Scale Image’, unlock the width/height and the X ppi/Y ppi, then double the X ppi and the width.
The above is useful particularly because non-square pixels can produce some odd effects (With 2:1 pixels, when you rotate a square 90 degrees, it becomes a rectangle twice as wide as it is tall!) so converting to square pixels can avoid these odd effects when needed.
I can easily follow the steps, but I need to see a practical application. David obviously has one. But when he says “If you want exactly 2:1 pixels” I need to ask “Why do I want 2:1 pixels?”
I have no experience with display devices other than my monitor, which has a resolution of 1024 x 768 pixels. If I create an image in Gimp that looks good on this monitor and I display it on a device with a different aspect ratio, I guess the image will appear distorted. Is this the motivation? That is, do I use this technique to change the pixel size in my image so that it renders properly on the new display?
I’m still catching up by watching all the episodes, and I hope to catch up with everyone soon!
For a display with a different aspect ration the image must be cropped or patched up with black bars – like with a film on a (old) TV screen. You either have broad black bars on top and below or you don’t see the sides of the image.
Most screens have square pixels, equal in width and height. This should be true for all computer monitors. If you make an image with a square crop it will be a square here too, even when I use a wide screen monitor.
But some displays use rectangular pixels – and for them you have to distort the image. These displays are used in special devices (I had a MP3 player with such a display) and when you make an image for these things you need these settings. So it’s very special and perhaps of not much use for most of us.