I'm tempted to provide the highest resolution icon and let iOS scale it down as necessary. Is this a bad idea, and (if so) why?
you'll definitely want to produce files of various sizes as required by xCode. You want to make sure that the file presented when the app runs is of a high quality.
There are tools out there that will automatically create all the sizes you need for your app icon. Here is a link to the site that I use: https://makeappicon.com/
Hope that helps!
Yes, it might be bad idea. If your icon art was produced using a vector image editor (e.g., Adobe Illustrator, Adobe Photoshop with vector primitives, Sketch, etc) you best bet is to export all required resolutions yourself. In doing so, you will guarantee the best possible output for each resolution.
Keep in mind that exporting a single high resolution image and then resizing, for each required resolution, using a bitmap editor (e.g., macOS Preview) won't produce the same results.
PS. As already pointed out, I'm not sure your binary will even be accepted by Apple if missing icon data :-(
I have big image textures (4-12MB) and have resized them as much as I can without losing too much detail and would like to further compress them. Online compressors compress the 12.6MB image to 6MB without any problems, but Xcode doesn't support it (even though the compressed image is still .png), apparently because indexed color spaces are not supported for bitmap graphics contexts (according to CGBitmapContextCreate documentation and another post) and the compressed image uses them. If I try to use it I get an error:
CGBitmapContextCreate: unsupported color space.
I was looking through Apple documentation about compression and supported formats, but all I can find is information about how to compress images in code. I want to be able to apply an compressed (or otherwise reduced in size) image in the editor itself and not later in code. Is this possible?
If it is not possible to do this using a program, how should this be done via code in Swift? I found a lot of objective-C posts about this, but none that uses Swift.
Important: iOS does not support device-independent or generic color spaces. iOS applications must use device color spaces instead.
Use CGColorSpaceCreateDeviceRGB as the color space.
I have been looking at SVGKit and I am finding conflicting ideas. Some say it's slower than PNG and others saying it is fast.
I was hoping to get a recommendation and which route I should take. When I am exporting my vector graphics to PNG for display, would it not make sense to use an SVG instead ?
Of course this gives the added value that it remains a vector.
Or is it still recommended in exporting everything to a PNG ?
You might consider the middle-way introduced in Xcode 7. Here you add your assets to the project as vector images (PDF) and at build-time Xcode automatically generates the PNGs in all needed sizes (1x, 2x, 3x).
Personally, I only use SVGs when necessary, like if I need to be able to change the color of the (parts of the) image. I believe there can be a performance hit when resizing vector images at run-time, although Android uses vectors as default, so it might be insignificant.
SVG is most resource intensive and can be used if you need to display something that can be zoomed in and out while PNG should be preferred for most UI graphics (logos, icons, etc.), as it is crisp yet remains lightweight and fast to display so there is no way to compare SVG with PNG in term of Performance.
if you are going after a Crystal clear images you can use pdf based graphics, which are supported by Xcode Using Vector Images in Xcode
if you still need to implement SVGKit i always suggest using some tools (like SVGCleaner) to clean and simplify SVG in order to enhance performance.
I have a simple question for anyone who knows the answer to this... I am making a social photo sharing app and I want to save a large enough image in the app so that it can be used in a full screen website app moving forward. Think...Facebook.
I've been playing around with JPEG compression in iOS and also testing sizes and quality with Photoshop CS5. I get really different results with these two. In photoshop, even at high compression, the image is quite clear and retains lots of detail. In iOS, once the compression dips below about 0.5 it looks horrible and blocky. It almost seems like there's a point where the image quality just dips after a certain magic compression number.
With photoshop, I use the "Save for Web" option and with iOS I am using UIImageJPEGRepresentation(image, 0.6). Is there a huge difference in these two? Aren't all JPEGs use the same kind of compression?
I am really not that informed in this world of image processing. Can anyone advice me on what is a good way to have images compressed to a level that preserves quality and stay bandwidth friendly? I want my images to stay about 1280px in length.
Any advice on this or smarter ways to move JPEGS over the network is welcomed. Thank you.
If your app is producing images from an iOS device, you should continue to use UIImageJPEGRepresentation. I don't think it's productive comparing the UIKit JPEG compression to Photoshop's.
I would find a JPEG compression level you're happy with using the available UIKit APIs and go with that. When you're serving up 30+million images a second it might be worth looking at optimisations but until then leave it to UIKit.
I'm looking for software to create PNG8 format transparent images as per this article.
NOTE: I need a Linux solution myself, but please submit answers for other OSes.
pngquant does a good job of converting to PNG8 while preserving full transparency.
If you're size-conscious, you may also be interested in pngcrush, which can usually (losslessly) compress PNG files quite a bit.
I also needed a Linux solution and found pngnq to do a pretty good job. It seems to be designed specifically for creating 8-bit PNG images with alpha channels.
apt-get install pngnq # If on Ubuntu/Debian
For Mac: ImageOptim and ImageAlpha are GUIs that run pngcrush, pngquant, and various other normally command-line compression utilities. http://pngmini.com/
The link you provided references ImageMagick, which is an excellent toolkit for manipulating images on Linux.
Ah, if I remember correctly, when I have read this article some months ago, pngquant hadn't a Windows version. I see it has one now. So I tried it, and pngnq too.
The latter seems to do a slightly better job on the IceAlpha.png test image (from libpng.org), at the cost of a slightly bigger image (it can be post-processed with pngcrush or pngout anyway).
The dithering algorithms (the two of pngquant, the only one of pngnq) are different, and it might be worth having both tools, converting images with all algorithms and see what looks the best.
For the record, on the Windows side, IrfanView (4.10) displays these images very well (using the transparency level on each palette entry) while XnView (1.85.1) and GIMP (2.4) apply only a full transparency/opaque display, à la GIF: the light bulb given as an example in the linked article has a transparent background around it, but the orange part is fully opaque.
And the excellent utility TweakPNG shows we have a PLTE (palette, 222 entries) chunk and a tRNS (alpha values for palette colors, 222 entries) chunk. Even more, it allows to edit each palette entry, color and alpha level. It might be an interesting complementary tool for this format.
Note on IrfanView support: if it handles PNG8 correctly for transparency, it doesn't handle gamma information in PNG files: on the toucan image or the ping-pong image, I had to apply a gamma of 2.4 to get similar (lighter) colors.
Note also that IrfanView does an awful job of converting 32-bit PNG images to 256, allowing only one transparent color, which looks bad if full color was dithered!
I see that the GIMP manual states: "his “PNG8” format, like GIF, uses only one bit for transparency; only two transparency levels are possible, transparent or opaque. "
while the ISO/W3C standard states:
"The tRNS chunk specifies either alpha values that are associated with palette entries (for indexed-colour images) or a single transparent colour (for greyscale and truecolour images).". The PNG specification 1.2 added: "Although simple transparency is not as elegant as the full alpha channel, it requires less storage space and is sufficient for many common cases."
It looks like the unique transparent color is more implemented than the full transparency palette, alas. At least browsers get it right.
It depends on what exactly your original images look like.
If your images already contain 256 or fewer colors (RGBA values), you need only look at pngout (Windows) (Linux/BSD/Mac OS X ports), which you should already be using to optimize your PNG images anyway. It can't quantize images, but it can save them as 8-bit, including alpha transparency. Just pass in the /c3 (or -c3 on Linux et al.) color option to force it to save the image as PNG8.
If your images do contain more than 256 colors, you have a few more, but all less than perfect options:
Adobe Fireworks is probably the best option in terms of the resulting image quality. It will do the job if you only need to convert a few images, or if you don't mind relying on Fireworks to do the batch processing. I did find that it sometimes somehow limits the number of colors in the palette, creating a worse quality image than necessary. I don't know if that's perhaps a bug in CS3 that's been fixed in CS4.
If you're not on Windows or OS X this obviously isn't an option, and buying Fireworks just for this probably isn't worth it either.
The only alternatives I know of are the already mentioned pngquant and pngnq. I've had better luck with pngnq, but that's probably just going to depend on which quantization strategy works best on the files you're working with.
Unfortunately, I've noticed that neither of them work very well with small amounts of transparency (say, an opaque image with transparent, rounded corners).
I recommend "The GIMP" as it is possible to output in PNG8 and supports Linux/Windows. If you want a quick Windows-only solution, I also recommend IrfanView.
Microsoft Windows: Ultimate Paint (freeware and shareware
versions are available).
Both versions can save as an 8 bit transparent PNG image.
It can also save as a 4 bit PNG (16 colours). This cuts the
file size in half compared to 8 bit.
Input formats include BMP, GIF, ICO, JPG/JPEG and PNG.
The freeware edition of Ultimate Paint Standard 2.88 LE can
be downloaded directly from
http://www.ultimatepaint.com/up.zip (1.7 MB).