I am developing an iPhone app with skiing destinations being listed in an UITableView. The table view can contain up to 2000 cells. Every cell has a small weather icon of 25x25px (Retina 50x50). I am already using weather icons on the detail view of every destination. These icons are twice the size: 50x50px on the 3GS and 100x100px with Retina display.
As rendering pngs in a UITableView is pretty memory consuming I am not sure if I should use the larger images also for the table view or if I should design images half the size for the table view only. Of course this would increase the download size of the app by about 300 KB.
It would be nice if anybody could give me an advice if it is best to recycle larger images in the app or if it is best to design images for every resolution needed.
Thanks in advance
Martin
You definitely want to use 2 images. If you use 1 image, you are using more memory on non-retina screens, but the same on retina screens. Using 2 images uses the least memory. There should be no problem with memory whatsoever with what you are doing, so I'd venture to say that you are keeping the images in memory after they are needed, which is unrelated to the table view code.
A good thing about UITableView is that it's memory usage is not particularly related to the cell's sizes. The little hoops you have to jump through as the datasource are there so that the table can recycle cells, keeping the memory relatively fixed with respect to memory usage of a given cell.
Recycling cells trades speed for space, so there's a more legitimate concern about scroll performance. This is related to the setup effort per cell (since they are being recycled and re-setup all the time). Image size can be factor here, but I don't think so at the scales you're considering (50^2 or 100^2). This is the kind of thing best investigated by running on real hardware.
On binary size, I think you're correct that a single version of the images would reduce the app download. It's probably not a make or break factor at 300k, but kudos for considering it.
I am getting ready to design a new iPad app, which will be locked in landscape mode. It's going to be relatively image heavy, as it will be a sales utility for hotels and resorts. There will be quite a few "hero shots" of hotels, meaning full or half screen images meant to highlight the property.
With the jump in resolution between the 2 and the 3, I'd like for it to look presentable on both versions. What is the standard way of designing for this? Do I include the highest res shots possible for the 3, and then let it scale down in software when rendered on lower versions? Do I include two versions of every image? Do I include just the highest resolution that the 2 can render, and hope for the best on the 3?
Wondering if both a high res and low res image are required for iPhone Apps.
Having a duplicate copy increases file size which is something I need to cut down.
I've built apps in the past and only used high res, without #2x appended to the file name. The apps look great on Low res and High res devices. so...
Let me know
It is not required to have both image types. However, since the resolution is different for the Retina display you might build a Default image that looks nice on the iPhone 4 showing lot of details, but will look different on the other iPhones due to lack of correct resolution. Furthermore the image will be downsampled and if your UI fetish is big enough you rather provide two images than only one very good and take an accaptable sampled image.
I'm not sure if it is the best approach to skip one image just to reduce file size because most of the time the Default images are not the most relevant media part, since icons, sound files etc tend to use more space.
To conclude: I would suggest using both images and try to reduce the App size somewhere else.
My dilemma -
I have a universal app that holds a lot of images and icon (about 1,000).
In many cases i use the #2x version as is for the iPad version, in other cases it is to big even for the iPad.
I see 2 options:
Add a unique images for the ipad (large the app size).
Scale the images every time i use them?
Would like to hear notes or ideas.
Thanks
Shani
I think you will here different suggestions here. It really depends on your requirements and whether it is more important (mandatory?) for you to reduce the size of your app or make it more responsive at run-time.
Are you going to scale the images down one-by-one (meaning that in a view you will have only an image)? Or are you going to scale down a whole lot of images to display, e.g., in a table view? This will impact greatly the user experience...
As to the "every time", you could think about using a cache, so that you only resize each image just once. This would be like an intermediate solution, but again, it depends on your app (if very many images will be loaded, the cache will become very large, so in this case it could be suggested to go for option 1).
Also, the iPad 2 is pretty fast; iPad 1 a little less, so you could also take into account that.
In general, I don't think that scaling down will add much overhead, but YMMV...
According to Apple, the iPhone 4 has a new and better screen resolution:
3.5-inch (diagonal) widescreen Multi-Touch display
960-by-640-pixel resolution at 326 ppi
This little detail affects our apps in a heavy way. Most of the demo apps on the net have one thing in common: They position views in the believe that the screen has a fixed size of 320 x 480 pixels. So what most (if not all) developers do is: they designed everything in such a way, that a touchable area is (for example) 50 x 50 pixels big. Just enough to tap it. Things have been positioned relative to the upper left, to reach a specific position on screen - let's say the center, or somewhere at the bottom.
When we develop high-resolution apps, they probably won't work on older devices. And if they do, they would suffer a lot from 4-times the size of any image, having to scale them down in memory.
According to Supporting High-Resolution Screens In Views, from the Apple docs:
On devices with high-resolution screens, the imageNamed:,
imageWithContentsOfFile:, and
initWithContentsOfFile: methods
automatically looks for a version of
the requested image with the #2x
modifier in its name. It if finds one,
it loads that image instead. If you do
not provide a high-resolution version
of a given image, the image object
still loads a standard-resolution
image (if one exists) and scales it
during drawing.
When it loads an image, a UIImage object automatically sets the size and
scale properties to appropriate values
based on the suffix of the image file.
For standard resolution images, it
sets the scale property to 1.0 and
sets the size of the image to the
image’s pixel dimensions. For images
with the #2x suffix in the filename,
it sets the scale property to 2.0 and
halves the width and height values to
compensate for the scale factor. These
halved values correlate correctly to
the point-based dimensions you need to
use in the logical coordinate space to
render the image.
This is purely speculation, but if the resolution really is 960 x 640 - that's exactly twice as high a resolution as the current version. It would be trivially simple for the iPhone to check the apps build target and detect a legacy version of the app and simply scale it by 2. You'd never notice the difference.
Engadget's reporting of the keynote included the following transcript from Steve Jobs
...It makes it so your apps run
automatically on this, but it renders
your text and controls in the higher
resolution. Your apps look even
better, but if you do a little bit of
work, then they will look stunning. So
we suggest that you do that
So I infer from that, if you use existing APIs your app will get scaled up. If you take advantage of new iOS4 APIs, you can get all groovy with the new pixels.
It sounds like the display will be ok but I'm concerned about the logic in my game. Will touchesBegan positions return points in the new resolution? The screen bounds will be different, these types of things could potentially be problems for me.
Scaling to a double resolution for display purpose is straight forward, but will this scalling apply to all api's that input/output a screen coordinate? If not things are going to break aren't they?
Fair enough if it's been handled extensively throughout the framework.. I would imagine there are a lot of potential api's this effects.
For people who are coming to this thread looking for a solution to a mobile web interface, check out this post on the Webkit blog: http://webkit.org/blog/55/high-dpi-web-sites/
It seems that Webkit has solved this problem four years ago.
Yes it is true.
According to WWDC it appears that apple has build it some form of automatic conversion so that the resolution for applications will not be completely off. Think up-convert for dvd to HDTV's.
My guess would be that apple knows what most of the standards developers have been using and will already be using these for an immediate conversion. Of course if you are programming an application to take advantage of the new resolution it will look much nicer than whatever the result of apples auto-conversion is.
All of your labels and system buttons will be at 326dpi but your images will still be pixel doubled until you add the hi-res resources. I am currently updating my apps. If you build and run on the iPhone 4 sim then it is presented at 50%, go to Window > Scale > 100% to see the real difference! Labels are smooth, my images look shocking!