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.
Related
The images I am getting back from the photo library and camera are HUGE, and it takes a significant amount of time to send them over the network even in good conditions. I can't imagine a scenario in which I would need the full double-digit MB image, but maybe I'm missing something? Is it common practice to resize them before sending them over the network?
Yes it is common practice to alter an image's dimensions and compression so that it is appropriate for application.
As observed, by the default images from the camera are very large so that they can be displayed on large screens, printed to posters, zoomed and cropped etc without appearing unduly pixelated. So unless the app in question is a photo/image manipulating app, then resizing will almost certainly be beneficial in that it can improve networking, the app's memory foot-print and it's overall snappiness.
In terms of how to size and compress, while it is possible to store multiple versions of the image for each device that's being supported.
Practically, it seems that storing a single image at the dimensions required on the lowest resolution device but then only compressing it enough so that the higher resolution devices can scale up as needed without looking ugly seems to deliver reasonable results.
In terms of resizing, there are various posts on SO e.g. How do I resize the UIImage to reduce upload image size
I've also stuck gist for the UIImage extension I'm currently using to do this in my App over on GitHub here.
Have fun.
You can transform the image into data and then use this:
let imageData = image!.jpegData(compressionQuality: 0.5)!
It will make the quality less than usual with 50% to be able to save it quickly and smoothly
I'm making a Universal App using MonoTouch, and I'm adding my Default-Portrait.png file. That file alone (a 768x1004 .png file) is adding 711k to the size of the app. My app itself is only about 7 megs, so it's adding 10% just for the splash screen.
I could easily make this thing an 80k jpg file instead of a png, but the device doesn't seem to look for a .jpg file. Does anyone have tips for reducing the size of this launch art?
At this point, I'm thinking I might just leave the launch art out and load my own jpg and display it as soon as I have the ability to. That'll keep my app size down, but it's not as nice as having the launch art scale in immediately like most apps do.
Hmmm...given the screen of the iPad and the visual quality users are expecting, I'd just leave it like that.
But if you do want to reduce the disk space, try going to Project > Edit Project Settings > Build (tab at top), and searching for a parameter called "Compress PNG Files." Make sure that's checked. It'll run the pngcrush utility before loading the file onto disk (check the size of your IPA archive after to see if it had any effect).
pngcrush is nice as well, however that will not reduce the quality of you image. If reducing the quality of the image is an option for you, then you might try this tool: http://www.punypng.com/ - or just use an image editing tool to "optimize" the image ...
I recommend pngout if you want to really squeeze those PNGs down, and this won't cost you any quality. It simply removes unnecessary metadata (like pngcrush) and uses its own compression algorithm which is compatible with the regular decompressor used in PNG (zlib). It's really slow, though.
A simpler option is to try "Save for web" in your image manipulation program of choice. Exporting from Acorn (not just the regular save) sometimes gives me vastly smaller files. This is especially true for default images which have large, uniform areas in one colour (screenshots, a small logo in the middle of a black screen).
Is there any reason why you want to reduce the file size that badly? I don't think it matters in your case. I just checked 3 of my apps and the Default.png (of various portrait/landscape varieties) is between 29KB and 422KB, so whilst yours do seem a little heavy, your still way under the 3G download limit.
Are you positive it's adding that much to the size of the app? Did you compare a before and after?
Xcode uses pngcrush on the images for you. I know because I just tried to substitue jpegs for pngs and got the following result:
So, in short, there's not a lot to be done except simplify the image beforehand. Xcode will handle the rest.
I have an app that will display a bunch of images in a slideshow. Those images will be part of the bundle, thus distributed with the app.
All the images are photographs or photographic, etc.
I've read that it's preferred to use PNG as the image format, but seeing that the JPG version will be much smaller, I'd rather be using that.
Are there any guidelines which format to use and in which case?
PNG's are pixel perfect (non-lossy), and require very little extra CPU energy to display. However, large PNGs may take longer to read from storage than more compressed image formats, and thus be slower to display.
JPG's are smaller to store, but lossy (amount depends on compression level), and to display them requires a much more complicated decoding algorithm. But the typical compression and image quality is usually quite sufficient for photos.
Use JPG's for photos and for anything large, and PNG's for anything small and/or designed to be displayed "pixel perfect" (e.g. small icons) or as a part of a composited transparent overlay, etc.
Apple optimizes PNG images that are included in your iPhone app bundle. In fact, the iPhone uses a special encoding in which the color bytes are optimized for the hardware. XCode handles this special encoding for you when you build your project. So, you do see additional benefits to using PNG's on an iPhone other than their size consideration. For this reason it is definitely recommended to use PNG's for any images that appear as part of the interface (in a table view, labels, etc).
As for displaying a full screen image such as a photograph you may still reap benefits with PNG's since they are non-lossy and the visual quality should be better than a JPG not to mention resource usage with decoding the image. You may need to decrease the quality of your JPG's in order to see a real benefit in file size but then you are displaying non-optimal images.
File size is certainly a factor but there are other considerations at play as well when choosing an image format.
There is one important thing to think about with PNGs. If a PNG is included in your Xcode build it will be optimized for iOS. This is called PNG crush. If your PNG is downloaded at run time it will not be crushed. Crushed PNGs run about the same as 100% JPGs. Lower quality JPGs run better than higher quality JPGs. So from a performance standpoint from fastest to slowest it would go low quality JPG, high quality JPG, PNG Crushed, PNG.
If you need to download PNGs you should consider crushing the PNGs on the server before the download.
http://www.cocoanetics.com/2011/10/avoiding-image-decompression-sickness/
The Cocoanetics blog published a nice iOS performance benchmark of JPGs at various quality levels, and PNGs, with and without crushing.
From his conclusion:
If you absolutely need an alpha channel or have to go with PNGs then
it is advisable to install the pngcrush tool on your web server and
have it process all your PNGs. In almost all other cases high quality
JPEGs combine smaller file sizes (i.e. faster transmission) with
faster compression and rendering.
It turns out that PNGs are great for small images that you would use
for UI elements, but they are not reasonable to use for any full
screen applications like catalogues or magazines. There you would want
to choose a compression quality between 60 and 80% depending on your
source material.
In terms of getting it all to display you will want to hang onto
UIImage instances from which you have drawn once because those have a
cached uncompressed version of the file in them. And where you don’t
the visual pause for a large image to appear on screen you will have
to force decompression for a couple of images in advance. But bear in
mind that these will take large amounts of RAM and if you are
overdoing it that might cause your app to be terminated. NSCache is a
great place to place frequently used images because this automatically
takes care of evicting the images when RAM becomes scarce.
It is unfortunate that we don’t have any way to know whether or not an
image still needs decompressing or not. Also an image might have
evicted the uncompressed version without informing us as to this
effect. That might be a good Radar to raise at Apple’s bug reporting
site. But fortunately accessing the image as shown above takes no time
if the image is already decompressed. So you could just do that not
only “just in time” but also “just in case”.
Just thought I'd share a bit of decompression performance data...
I'm doing some prototyping of a 360 degree viewer - a carousel where the user can spin through a series of photos taken from different angles, to give the impression of being able to smoothly rotate an object.
I have loaded the image data into an array of NSData's to take file i/o out of the equation, but create NSImage's on the fly. Testing at near max frame rate (~25 fps) and watching in Instruments I see the app is clearly CPU-bound and there's an approximately 10% increase in CPU load showing ~275 kb png's vs. ~75 kb jpg's.
I can't say for sure but my guess is the CPU limit is just from general program execution and moving all the data around in memory, but that image decompression is done on the GPU. Either way and the JPG vs. PNG performance argument looks to favour JPG, especially when the smaller file sizes (and therefore smaller sizes of objects in memory at least in some parts of the chain) is taken into consideration.
Of course every situation is different, there's no substitute for testing...
I have found massive differences in animation performance when using jpegs vs png. For example placing three screen-sized jpegs side by side in a UIScrollView and scrolling horizontally on an iPhone4 results in lag and a thoroughly unpleasant jerky animation. With non-transparent pngs of the same dimensions the scrolling is smooth. I never use jpegs, even if the image is large.
I think if you want to use transparent, you have no choice except PNG. But, if your background is opaque already, then you may use JPG. That is the only difference I can see
'Use JPEG for photos' as mentioned in Human Interface Guidelines under section Produce artwork in the appropriate format.
I want to add high res images in my iOS4 app. I already read this http://developer.apple.com/iphone/library/documentation/iphone/conceptual/iphoneosprogrammingguide/SupportingResolutionIndependence/SupportingResolutionIndependence.html#//apple_ref/doc/uid/TP40007072-CH10-SW2 and a lot of other pages but I did not find the answer which ppi my image should have.
Currently, I have an image for example button.png with 160ppi and 50x30px. Now I want to create a high res image named button#2x.png. Is it correct to use 326ppi and 100x60px?
I already had a look at other iOS open source apps but each app did it on a different way. Most apps used 72ppi for normal and high res. What is correct?
Thanks for your answers
Walter
To be quite frank, I've not found a need to adjust pixel resolution for my images (i.e. I leave my Photoshop templates at 72 ppi and they're OK). If you just provide the correct dimensions for each format, the system will know how to deal with your images appropriately depending on the resolution of the device it's on.
Currently iOS supports three different art sizes: art for the 480x320 original iPhone screen, art for the hi-res 960x640 iPhone 4 screen, and art for the 1024x768 iPad screen, which in my experience is usually not the same as for the hi-res screen because of the different demands placed upon the different aspect ratio of the screen.
In a worst case, you could include three sizes for all of your artwork, and that's exactly what I did for the main element (cards) of my last game. However, it's ultimately wasteful in both download time and my time in creating them all.
What would y'all suggest as the best way to deal with the different requirements of the different iDevices? Here's a few general possibilities that I'm considering:
Include artwork in all 3 sizes.
Include artwork in just 1 size (the big one), but resize it on the fly as UIImages are created.
Include artwork in just 1 size (the big one), but make resized copies of it the first time a user starts up your app.
There are of course variants involving using some techniques for just some sizes (e.g., share artwork between the two big sizes, slightly resizing as needed). I'm interested in which method you'd use, with notes on the pros and cons of doing so. I expect the biggest cons are going to be: file size and any lag that might be caused in display or resizing of the objects. One of my biggest unknowns is how good of a job iOS does if you let it do the resizing, both in output quality and in timing.
I'm currently using artwork in all 3 sizes. If your artwork is in vector format and designed for both the iPhone and iPad aspect ratios, it's a simple batch action to create all 3 at the same time.
If you just include the highest resolution, the memory usage might be a problem with older iOS devices which have less memory to work with. The image quality and speed of resizing is not an issue, since both are excellent, if you let the OS resize the images. For me, I don't want to have additional code to handle resizing the same image for different devices. Otherwise it sounds like having just the large artwork and making sure it's resized correctly will be fine.