Taking help from here, I know that the resolution of iPhone 6 is 1334x750 and the density or the pixels per inch is 326 ppi. So, would I be adding an image with those measures to make it appear as is or maybe even the sharpest it could on the iPhone 5?
Some cases:
What happens if I add an image with a resolution of 1334x750 but with a density of , say, 100?
What happens if I add an image with a density of 326 ppi but with a resolution of , let's say, 1900x1500?
I have picked these values at random. I know the quality of the image would be affected a lot in these cases but I'm just curious how is the image being processed to be viewed on the phone.
Thanks in advance.
P.S. Feel free to edit the tags, I just added what I felt was appropriate.
Related
Why do we need these 3 particular image types?
If I have a button on my app with a background image say, 50 pixels x 50 pixels, why do I need 3 versions of this image? What's stopping me from just making one image that's much higher in res, say, 700x700 so when it shrinks down on any iPhone it won't fall under the max res the device would want?
Only thing I can think of is it just takes up more space, but for simple apps / a simple button it seems like it wouldn't cause any issues. I've tried it on a few devices and see no difference between them when I simulate it and do this method. However, as I dive more into apps and stuff I'm sure there is substance behind this technique.
If you don't have the exact size, there are two things that can happen:
Upscaling
#3x or #2x can be upscaled from #1x but usually the visual result is blurry, with thick lines and doesn't look good. Upscaling #3x from #2x can be even worse because subpixels must be used.
Downscaling
In general, the results are much better than with upscaling, however, that doesn't apply for all the images. If you have a 1px border on a #3x image, after downscaling it to #1x the border won't be visible (0.33px). The same applies for any small objects in the image. Downscaling destroys all details.
In general - for an image to look perfect, you want to avoid both downscaling and upscaling. You can always go with only #2x or #3x images and add other scales only if you see visual problems. Using higher resolution won't improve downscaling. High resolutions are used only to avoid upscaling. Downscaling from a high scale (e.g. #100x) to #1x won't create better results than downscaling from #3x.
You need 3 kinds of images in Image Assets because in terms of Scaling or Pixels
There are 3 kinds of Apple Devices (iPhone and iPad) that is
Normal device which terms to 1 pixel = 1 point#1x (Older iPhone and iPad devices)
Retina device which terms to 4 pixels(2 x 2) = 1 point#2x (iPhone 4+)
Retina iPhone6 and iPad which terms to 9 pixels (3 x 3) = 1 point#3x (iPhone6+)
Thus for providing same image in 3 scales iOS decides which image to show for which devices.Hope could help you understand this.
EDIT
It is because if you provide one high resolution graphic it would be waste of space on a users' device. Thanks to app slicing the device will download (from App Store) only the parts that actually fits the device (so retina device won't download non retina graphics). This is why Apple created assets catalogs and this kind of rules to follow. They describe it in their sessions.
In short it is to decrease memory/disk usage so it is all about increasing performance and user experience
First of all, you need to know points vs. pixels behaviour. On non-retina devices, point vs pixels ratio is 1point=1pixel. On retina devices, there are two ratios: 1point = 2x2 pixels depending on screen size, and 1point=3x3 pixels, because of pixels density, that is quadrupled watching on non retina. That's why you need this 3 types of images, to be shown on its highest resolution.
Complementing what Sulthan said:
Because you didn't propitiated proper images for a specific device, it has to downscale or upscale. These processes will use up your memory and processing, resulting maybe in a decrease of performance, depending on how many images at a time you're doing it and the size of image.
If you provide only one big image you encounter several problems:
Downscaling leads to the loss of quality (even if it is not huge)
It takes more computational power to downscale the image than to display the already pre-rendered image
The size of your binary gets increased and you are not able to benefit from app thinning which is introduced with iOS 9.
As you can see, producing only one image will impact the performance and quality of your app and it will disproportionately hit those with older devices. This is because:
They need to downscale more. Also, the performance of their devices is not as good as that of the new ones, so they are much more likely to notice the lags with your app
They do not have as much storage space so you really want to be able to use app thinning to help them
The loss of quality will be the highest for them and considering the fact that the resolution of their devices is low, they will notice it.
Due to this users are likely to be unhappy and this is bad for you. Because, from my experience, unhappy users are 10 times more likely to rate your app than happy users. You don't want that, do you? :)
The apple guides haven't helped me too much with this but I am starting to get serious about IOS development and was taken aback when I saw images go from #1x to #3x.
One source I found said they were based on sizes. For example:
If you are working on an inferred VC size and your image is 30x30 and you run that on a iPhone6 then your image should be 30x30 for #3x, 20x20 for #2x, and 10x10 for #1x.
Another source I said mentioned that it was based off the images resolution and not the size of the image.
Could someone clear this up for me and explain how to make sure my images look professional for all screens?
Thanks in advance!
When the first iPhone (and SDK) came out, all images were 1x (1 pixel of the image = 1 pixel of the screen), because that's all we had to care about. On that phone there were 166 horizontal or vertical pixels per inch (dpi). So to display an image that stretched from the left edge to the right edge, our image would need to be 320 wide (because that's what Apple told us - we didn't have to count pixels) by whatever height we wanted. Let's say 100 pixels tall. We'd name that image MyPhoto.png (because Apple told us the iPhone OS worked best with PNG images) and we'd display it.
When the iPhone 4 came out with the retina display, its retina display had 2 times the horizontal and 2 times the vertical resolution of the older phones. So now we needed higher resolution images to get the best looking interface. We were still displaying just a 2" wide image, but it would need twice the number of horizontal pixels and twice the number of vertical pixels (4 times the total number of pixels) to fill the same space. So now our image needs to be 640 pixels by 200 pixels. Since our app would still need to support the older phones as well as the new phones, we didn't want to just replace the old image with the new one. We needed a way to support both. So the old images kept the same name they had before (we didn't append "#1x") and the new images got the "#2x" filename extension to indicate they were twice the resolution. So we'd name this larger image MyPhoto#2x.png.
A common question is why not use just the higher resolution images on both old and new phones? With scaling, both appear to work great. The problem primarily is that the iPhone, especially the older phones, had very limited memory to work with. Using images that are 4 times larger than they need to be is really hard on that limited memory. That's why we had to have both 1x and 2x images in our apps.
For our sanity, we would still just use 1x while designing the interfaces. So screens remained 320 pixels wide in our code, even if we were going to display them on a retina display that was 640 pixels wide. If we wanted to draw a 1 pixel wide line on the retinal display, we'd make it half a pixel wide in our code.
With the larger screen of the iPhone 6 Plus, Apple had to pack even more pixels on the screen to maintain the high resolution customers came to expect. So now we're into 3x images. However, the iPhone 6 Plus doesn't really have three times the number of horizontal or vertical pixels. But again Apple has kept us sane by just asking us to supply "#3x" images, and it worries about scaling them down a bit on the device. As before, we still need to support smaller screen resolutions too, so we still include "#2x" and the 1x images in our apps.
So, to continue our example, the #3x image would need to be three times the width and height of the 1x image. So now we need a 960 wide by 300 pixel tall image. We'd name it MyPhoto#3x.png.
Notice that although I mentioned earlier something about a 166 dpi display, that's not really important when creating these images. In your photo editing app you don't really care if the image is 166 or 72 dpi or anything else. The only important part is the number of pixels in width and height of the final image we export.
So to answer your question (hopefully), you'll want to include all three of these images in your iPhone compatible apps. You can skip the #3x image for iPad-only apps, because there's no 3x screen yet for the iPad. But continue to think only in the 1x size when working in Interface Builder and code.
For example, now to display a 1 pixel wide line on the iPhone 6 Plus, you'd draw a 0.33 wide line rather than a 1 point line. Of course, you still want to support all of the other screen resolutions too, so you'd use code like this to set your line width:
let lineWidth = 1.0 / UIScreen.mainScreen().scale
This will give you 1.0 for the non-retinal iPhones, 0.5 for the iPhone 4, 5 & 6, and 0.33 for the iPhone 6 Plus.
is it not enough to supply just 3x resolution image (e.g for a view or button) in Xcode so that it looks good on iPhone 5,6,and 6plus devices
( i.e leaving 1x and 2x in an image set blank )
My reasoning is that 1x image may look blurry on 6 plus but 3x image should look fine on 5
Basically i am asking so that i can communicate the same to my graphic designer and he should be fine with supplying a singe size rather than three sizes for all images
This got asked and answered many times regarding 2x assets, and the answer hasn't really changed (but it's hard to track down duplicate questions when I'm posting from my phone).
If you ship assets with a higher scale factor than the target device, they will display just fine. But downscaling them in real time has performance costs—they use more memory, they take longer to upload to the GPU, they take GPU time to render. Some of these costs are trivial, others aren't. (Remember, a 2x image is 4x the data of a 1x one, and a 3x image is 2.25x the data of a 2x one.) And they add up for every image in your app.
Most importantly, the devices with lower scale factors are the ones with less CPU/GPU/memory resources to spend on downscaling.
So, what to do? Well, if you don't want to have your artist deal with multiple scale factors, just order the 3x artwork and scale it yourself in Photoshop (or heck, even Preview) before you ship. It might not look as nice as if your artist tweaked it for each size, but it'll look about as good as real-time scaling without the run-time performance costs.
Or, with Xcode 6, you can put a PDF in your asset catalog, and Xcode will automatically generate PNGs for each size at build time. (This is an Xcode feature, not an iOS one, so it works even if you're targeting iOS 7.)
The problem with this idea is that in iOS 8 the iphone 4S is still supported and it has a different aspect ratio than every other iPhone. It renders at 320x480 at 2x so creating images to fit this wouldn't look grainy. The other 3 screen sizes would work if you go with the 3x scale which would be 1920x1080 for every page and just downscale the size for the 4in and 4.7in screens. You will likely need 2 story boards for the app (one for 3.5in and then the other for the 3 other screen sizes). Auto-sizing wouldn't really work in this case unless you changed the image of the UIImage because it would have a shortened length while maintaining the same width.
EDIT: changed the iPhone 6+ screen size to account for the 1.15x down scaling
and changed the rendering factor to match the comment below
We are currently working with a design who is supplying Retina images to us with odd dimensions i.e. 28 x 15 px which I believe is incorrect as when you divide it you get an odd number like 14 x 7.5 px.
This is a rule I have always worked on but the designer is not getting the point and I thought I should double check what the exact rules are.
I've had add look on the web but cannot seem to find any references on this so it would be great to hear what everyone thinks on this matter.
Thanks
Yes you can, but NOT recommend.
For example, if you have an #2x image with 28 x 15px , your normal image will be 14 x 8px.
If you look close into the normal image, the pixels are not aligned well.
It is always recommended to use even number of pixel in dimension.
The #2x image needs to be exactly twice the width and twice the height of the standard image, or the automatic loading of it won't happen - your app will load and pixel-double the non-Retina image.
The standard image file will as a matter of course be a whole number of pixels wide and high, so you'll need the #2x to be even in its dimensions.
Tell your designer to catch on ;)
It's not possible because in Xcode you design your application with classic resolution pictures, and you can't use a float for width or height. So, you will have a one pixel gap difference between your classic and retina design. Maybe the easiest way to solve your problem is to add a transparent line of pixels in your high resolution picture.
My current resolution of all the pictures (all of png format) in my app is 300, which I realized is too high,
I heard that 72 ppi will be enough, but however I just wanna make the best vision effect of these pictures,
so what is the best resolution of pictures for IOS app? both Retina and former screens.
And one more question, I tried to save my pictures in photoShop to 72 ppi,
but after I drag that picture to my XCode project, XCode tells that the resolution is 71 pixels/inch,
would it be a problem?
THanks a lot!
The answers to your questions can be found here.
But in short, 72 dpi is what you want. Retina screen imagery is termed 'High Definition' but is simply twice the size as non Retina imagery, i.e. your app icon is nominally 57x57 pixels but your retina variant of the same icon is 114x114 pixels (both images being 72dpi).
Re: your photoshop query. I have no idea about photoshop itself but in this instance I can't imagine why an image less than 72dpi would cause too great an issue. Photoshop gurus will be able to tell you why this is happening.