I'm having a real hard time understanding this, but let's say I have an iOS app for both iPad and iPhone and I want to download an image from a server and display it in full screen.
I have read that the iPad pro has a resolution of 2732x2048 and if we want to display an image in fullscreen we would need to download the image with this size right? However, I also read that the image should never be over 300KB. I was not able to bring an image with this size under 2MB (I used JPEGmini for example to reduce size).
And I don't think that iPhone user would need to download such a huge image, so my question is: what resolution should my images be on the server and how can I manage to keep them in a rational file size. Also should I upload multiple images for different devices? If so, how many and at what resolutions?
Isn't the problem merely that you are holding incompatible beliefs? This is the belief that is giving you trouble:
I also read that the image should never be over 300KB.
Let go of it.
Clearly it is right to say that the image should be no larger than needed for display. But an image to be shown as a 3x scale image on the iPad pro needs to be 2732x2048. So that's that.
(You could, alternatively, use an image 2/3 of that size and show it as a 2x scale image. It wouldn't look quite as good as the 3x scale image, but it might be acceptable.)
On a smaller device, yes, you should scale down the image in code, so that you are not holding in memory an image larger than needed for display. But in this case, you need the large image for display.
Related
I understand how 1x, 2x and 3x image resolutions work but I'm unsure how I go about choosing the right size/resolution for custom images in general. Imagine that we have a simple layout like the following:
Now it is up to me to create the image (in Photoshop for example) for that UIImageView. What size and resolution should the highest quality version be? Do I just use the highest screen resolution of the iOS devices that are currently available as my guide?
There is not really a best size. As you said the highest screen resolution would be the maximum, because the device obviously can not display more pixels than it has provided. If the image view is only about 1/5 of the screen size then I would use a smaller image size for memory usage.
And you only need one size for background images for example. I normally place them in my assets folder into the 2x place and I am good.
For icons i use 25x25, 50x50 and 75x75 (which will display really small on the screen)
hope I could help you a little bit…
I've built a website that stores images in 4 different sizes on the file system. It keeps the origional file size, medium, thumb, small image and resizes them as they upload.
We then created the web api to allow us to build the ios/android apps.
while building the apis our overseas developer then asked to provide the image dimensions along with the image file name. it took a lot of work regarding calculating the image sizes and saving them to the database.
{ "imagefilename" : "someimage.jpg", "LargeimageHeight" : "1000",
"LargeimageWidth" : "500", "mediumImageHeight" : "500",
"mediumImageWidth" : "250",
"smallImageHeight" : "100", "smallImageWidth" : "60" }
with the amount of image sections we have in the website made it a task and i want to know if this is really nessesary. Im not an ios developer but not really sure as to why the additioanl dimensions of the image need to be saved and or really needed.
i thought the ios has the image feature (#3x) (#2x) (#3x) ??
or do i use 1 specific folder image size for ios ??
does this always happen in the ios world for images that the code needs to know the image dimensions for the best result?
thanks
If your iOS application show images in flow layout (like pinterest style) you must return image dimensions. Otherwise I don't think its nessesary
Do you need the return the image dimensions:
Short answer: no. You can load the image using UIImage, and call image.size.height and image.size.width.
Long answer: maybe, depending on the interface design of your application, and if every image has different dimensions, it might take a performance toll to load the image into memory before being able to get its size (and probably do autolayout and have it render on screen). You might have issues with scrolling speed, but it will depend on the specific design and requirements.
What is the #2x #3x iOS image feature
iPhone and iPad screens come in different pixel densities (non-retina, retina and the retina iPhone 6+ screen). If you have a local image, stored on the phone, it can preload the image with the right scale automatically, by just providing the base name of the image, if you add the right suffix to each asset like name#2x, etc.
Sadly, it doesn't work the same for remote images see this answer. You will have to check yourself for the scale and load the right image, or load one big file, and let it be resized on the device.
You should consider providing dimensions inside your API response.
Think design:
When you scale your app to have many images at once, or when you distribute your app to multiple devices, you may realize the advantage. Your iphone 4 may end up downloading the image (worse, images) intended for iPhone 6S, and so on. If the reverse is true, it's even scary to think about.
How about the device asking for the image it's best suited for?
As for scaling of images, Bram De Geyter is correct - you can render whatever resides on the device, not fetch the correct one from the server. So having your API giving you the right dimensions is the only solution.
I have described the whole image loading from API approach in my blog here.
I am displaying a grid of images (3rows x 3 columns) in collection view. Each image is a square and its width is determined to be 1/3 of collectionView's width. Collection view is pinned to left and right margin of the mainView.
I do not know what the image height and width will be at runtime, because of different screen sizes of various iPhones. For example each image will be 100x100 display pixels on 5S, but 130x130 on 6+. I was advised to supply images that exactly matches the size on screen. Bigger images often tend to become pixelate and too sharp when downsized. How does one tackle such problem?
The usual solution is to supply three versions, for single-, double-, and triple-resolution screens, and downsize in real time by redrawing with drawInRect into a graphics context when the image is first needed.
I do not know what the image height and width will be at runtime, because of different screen sizes of various iPhones. For example each image will be 100x100 display pixels on 5S, but 130x130 on 6+
Okay, so your first sentence is a lie. The second sentence proves that you do know what the size is to be on the different screen sizes. Clearly, if I tell you the name of a device, you can tell me what you think the image size should be. So, if you don't want to downscale a larger image at runtime because you don't like the resulting quality, simply supply actual images at the correct size and resolution for every device, and use the correct image on the actual device type you find yourself running on.
If your images are photos or raster type images created using a raster drawing tool, then somewhere you will have to scale the original to the sizes you want. You can either do this while running in iOS, or create sets up front using a tool which can give you better scaling results. Unfortunately, the only perfect image will be the original with everything else being a distortion of the truth.
For icons, the only accurate rendering solution is to use vector graphics. Tools like Adobe Illustrator will let you create images which you can scale to different sizes without losing clarity. Unfortunately this still leaves you generating images up front. You can script this generation using most tools and given you said your images were all square, then the total number needed is not huge. At most you need 3 for iPhone (4/5 are same width, 6 and 6+) and 2 for iPad (#1 for mini/ipad1 and #2 for retina).
Although iOS has no direct support I know of for vector image rendering, there are some 3rd party tools. http://www.paintcodeapp.com/ is an example which seems to let you import vector images or draw vector images and then generate image code to run in your app. This kind of tool would give you what you want as the images are now vector drawings drawn at the scale you choose at run time. $99 though.
There is also the SVGKit (https://github.com/SVGKit/SVGKit), but not sure how good/bad this is. It seems to let you simply load and render direct from SVG files. Might be worth trying.
So in summary, I think you either generate the relatively small subset up front using a tool you can control the output from, take the hit in iOS and let it scale the images or use a 3rd party vector to image rendering kit which would give you what you want.
I was thinking to write some quiz app where questions are represented as images.
My question is, for each quiz question (question.jpg), and thus a jpg file, do I have to create
a double sized question#2x.jpg file?
Is it necessary?
Doing this seems will increase size of my program so I was thinking when/if this is necessary to do?
PS. And in case I have to do it, I will just have to double in size each image manually and add to the project right (both original and double sized image)?
PPS. Just to add more info. The questions are located on the web site, I have to download them and add to my project manually (like resources). On web site there are no different versions of the same image. So, I have whatever is on the web site. Some images I noticed are 800x600 in dimensions but some are also in dimentions 500x400. So after I download these images, how shall I name them? Just with original names? and forget about the #2x extension? What's the best practice?
(if this will help my image view will probably be smth .like 310 in width). Do I have to modify them in size? What to do?
Apple's naming conventions of high resolution images can be found here:
Apple doc naming conventions
If you are developing in the way that you want to support old screen as well as retina screens. You can use xxxx.jpg for old devices as iPhone 3gs and iPad 1, and use xxxx#2x.jpg for retina displays. Where the aspect ratio needs to be the same but the #2x image needs to be twice as big.
In your case "my image view will probably be smth .like 310 in width", then the #2x image needs to be 620px in width and normal revolution 310px.
There is actually no need to have both image sizes in the app as you can use the same image and just scale it(If you really really need to have the old resolution supported).
Even if you add just a #2x, it will scale itself if someone on an old device installs your app. It may become a bit blurry but will still be quite ok.
If you are planning to use a lot of images in your app I suggest using some sort of web service where the user can download content that is to be shown. But that's just me. As the app will quite quickly become very large as images takes up quite a bit of space. Of course this all comes down to how many images you will have.
The drawback of using a web service is that the user much have an internet connection to be able to play. And download your content.(Most quiz apps I know of does use a web service for this.) This is a matter of taste.
If you do need to support normal and #2x here us a method you can use. This method will return the scaled image so you just need the normal one or the #2x one and then scale to the other size. This will at least help you a bit when it comes to getting either your app size down or your clients download time down.
If you are using .jpg's and scaling them upwards you can quite easily get a pixalated image as it is a lossy format. But if that's what you still want to do and maintain aspect ratio, this is one way to do it:
-(UIImage*)resizeImage: (UIImage *)imageToScale withScale:(CGFloat)theScale{
UIImage *image = [UIImage imageWithCGImage:[imageToScale CGImage]
scale:(imageToScale.scale * theScale)
orientation:(imageToScale.imageOrientation)];
return image;
}
Usage
[self resizeImage:[UIImage imageNamed:#"question.jpg"] withScale:0.5];
0.5 would double the size and 2.0 results in an image half the size as the original.
If you want a more complex method to set for instance set a specific target size just say so and I'll edit this answer.
I'm releasing a new update for one of my apps and I was disappointed to see that it just barely surpasses 20MB estimated size (20MB is the point where it can no longer be downloaded over cell data).
My app contains a lot of images, so I could greatly reduce the size if I didn't have all those non-retina images. I know that there are some non-retina devices that will be running my app. So here are my questions:
How will a non-retina device react if I have an image with the #2x suffix but no non-retina image without it.
If I use a retina sized image without the #2x suffix and scale it down to the size I want to display it at programmatically and/or
through interface builder, will it still maintain full quality on
retina devices? Will the quality be worse on a non-retina device
than using an image I downscaled from the original using GIMP
instead?
How will a non-retina device react if I have an image with the #2x suffix but no non-retina i
image without it.
I use that approach on a couple of apps of mine and it works flawlessly. I am not able to detect any performance or visual issues on non-retina display devices (concretely, iPad 1/2 and mini).
I am not sure what can happen on older iOS version, since I only support iOS5+ on those apps.
If I use a retina sized image without the #2x suffix and scale it down to the size I want to display it at programmatically and/or through interface builder, will it still maintain full quality on retina devices? Will the quality be worse on a non-retina device than using an image I downscaled from the original using GIMP instead?
This comes down to how you set interpolation options while doing the scaling. See this other question for more details on how interpolation quality affects scaling down an image. In GIMP or Photoshop you also have control on the interpolation to be used for scaling, btw.
But in the end I don't think you need to go this way.
Most importantly, that bandwidth limit has been raised to 50MB.
OK.
If you only provide one image then you have one of two possibilities.
The image is a non-retina image. This will look fine on the non-retina. It will look identical on a retina device. But will look low quality next to a retina image.
The image is a retina image. On the retina device it will still load as a retina image. It will look fine. However, on the non-retina device it will have to scale down the image. This takes extra cycles of the CPU so could affect performance and it may not look how you want. It may shrink the image using a different method than you want and so may make the image look odd.
This is the same with or without a suffix.
The best solution is to create retina images and then use your editor of choice to create the standard versions. Nothing will stop you only providing one image but it may lead to a look and performance that you don't want.
On a side note. The size for downloading over cellular data was increased to 50MB.
Try these things using the simulator and find out for yourself.
I think the answer is that UIImage will ignore the #2x choice if you're relying on [UIImage imageNamed:#"without2xSuffix.png"] and not find anything, but I haven't tried it. Deliberately requesting the #2x file will work, but whether the image will be scaled, tiled, stretched or centered (or something else) is up to the place where it's used.
Note that the documentation says that unless you use the name without the #2x suffix and let iOS find the 2x version for you, it will set the scale of the image to 1.0 rather than 2.0, which complicates drawing. You'd have to load the image using imageWithData:scale: to fix this.