Mipmap drawables for icons

Question

Since Android 4 3  Jelly Bean  we can now make use of the res mipmap folders to store  mipmap  images   For example  Chrome for Android stores its icons in these folders instead of the more normal res drawable folders   How are these mipmap images different from the other familiar drawable images   I see that in my manifest  we use the  mipmap  qualifier  instead of  drawable   which makes sense given the resource folder name    lt activity     android name   MipmapDemp      android icon   mipmap ic launcher    gt      References   The Android 4 3 APIs document has the following to say      Using a mipmap as the source for your bitmap or drawable is a simple   way to provide a quality image and various image scales  which can be   particularly useful if you expect your image to be scaled during an   animation       Android 4 2  API level 17  added support for mipmaps in the Bitmap   class   Android swaps the mip images in your Bitmap when you ve supplied   a mipmap source and have enabled setHasMipMap    Now in Android 4 3    you can enable mipmaps for a BitmapDrawable object as well  by   providing a mipmap asset and setting the android mipMap attribute in a   bitmap resource file or by calling hasMipMap      I don t see anything in there that helps me to understand     XML Bitmap resources have an android mipMap property      Boolean  Enables or disables the mipmap hint  See setHasMipMap   for   more information  Default value is false    This does not apply to launcher icons as far as I can see     The question was raised on Google Groups  The purpose of resource name  mipmap      to which Romain Guy replied      It s useful to provide an image at a larger resolution that would   normally be computed  for instance  on an mdpi device  Launcher might   want the larger hdpi icon to display large app shortcuts     I feel like this almost makes sense of it  but not quite   I m still inclined to go with Randy Sugianto s follow up      What are the advantages of this  Is there any guide how to use   mipmaps  probably for better launcher icons      Of course  Wikipedia has a page for  Mipmap   which refers to an older technique invented in 1983  that I can t quite relate to the current Android implementation     Should we be storing all our app icons in res mipmap folders these days  and what are the guidelines for these mipmap images     Update  1  Here s a blog post that tries to explain it a bit    Mipmapping for drawables in Android 4 3   But the image used in that blog post shows what looks like one file with many logos in it  This is not what I see in Chrome s mipmap folder   Chrome s mipmap-hdpi folder contains three images  One is the Chrome logo  on its own     Strangely  it is 72x72  not 48x48 which I would expect to see   Perhaps that is all there is to this - we just need to keep bigger icons in the mipmap folders     Update  2  The Android Developers Blog post of 23 10 2014 again confirms the idea of using the mipmap folders for application icons    Getting Your Apps Ready for Nexus 6 and Nexus 9   When talking about the Nexus 6 screen density  the author writes      It   s best practice to place your app icons in mipmap- folders  not the   drawable- folders  because they are used at resolutions different from   the device   s current density  For example  an xxxhdpi app icon can be   used on the launcher for an xxhdpi device      Update  3  Note that Android Studio creates the ic launcher png icons in the mipmap    folders rather than the drawable    folders that Eclipse used to create them in

User · Answer

There are two cases you deal with when working with images in Android          You want to load an image for your device density and you are going to use it    as is     without changing its actual size  In this case you   should work with drawables and Android will give you the best fitting   image    You want to load an image for your device density  but this image is going to be scaled up or down  For instance this is needed when you   want to show a bigger launcher icon  or you have an animation  which   increases image   s size  In such cases  to ensure best image quality    you should put your image into mipmap folder  What Android will do is    it will try to pick up the image from a higher density bucket instead   of scaling it up          SO      Thus  the rule of thumb to decide where to put your image into would   be          Launcher icons always go into mipmap folder    Images  which are often scaled up  or extremely scaled down  and whose quality is critical for the app  go into mipmap folder as   well    All other images are usual drawables       Citation from this article

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The understanding I have about mipmap is more or less like this   When an image needs to be drawn  given we have different screen sizes are resolutions   some scaling will have to take part   If you have an image that is ok for a low end cell phone  when you scale it to the size of a 10  tablet you have to  invent  pixels that don t actually exist  This is done with some interpolation algorithm  The more amount of pixels that have to be invented  the longer the process takes and quality starts to fail  Best quality is obtained with more complex algorithms that take longer  average of surrounding pixles vs copy the nearest pixel for example    To reduce the number of pixels that have to be invented  with mipmap you provide different sizes rsolutions of the same image  and the system will choose the nearest image to the resolution that has to be rendered and do the scaling from there  This should reduce the number of invented pixels saving resources to be used in calculating these pixels to provide a good quality image   I read about this in an article explaining a performance problem in libgdx when scaling images   http   www badlogicgames com wordpress  p 1403

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res  mipmap-mdpi ic launcher png  48x48 pixels  mipmap-hdpi ic launcher png  72x72  mipmap-xhdpi ic launcher png  96x96  mipmap-xxhdpi ic launcher png  144x144  mipmap-xxxhdpi ic launcher png  192x192    MipMap for app icon for launcher  http   android-developers blogspot co uk 2014 10 getting-your-apps-ready-for-nexus-6-and html  https   androidbycode wordpress com 2015 02 14 goodbye-launcher-drawables-hello-mipmaps

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One thing I mentioned in another thread that is worth pointing out -- if you are building different versions of your app for different densities  you should know about the  mipmap  resource directory   This is exactly like  drawable  resources  except it does not participate in density stripping when creating the different apk targets    https   plus google com 105051985738280261832 posts QTA9McYan1L

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Since I was looking for an clarifying answer to this to determine the right type for notification icons  I d like to add this clear statement to the topic  It s from http   developer android com tools help image-asset-studio html saving     Note  Launcher icon files reside in a different location from that of   other icons  They are located in the mipmap  folder  All other icon   files reside in the drawable  folder of your project

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It seems Google have updated their docs since all these answers  so hopefully this will help someone else in future    Just came across this question myself  while creating a new  new new  project   TL DR  drawables may be stripped out as part of dp-specific resource optimisation  Mipmaps will not be stripped      Different home screen launcher apps on different devices show app launcher icons at various resolutions  When app resource optimization techniques remove resources for unused screen densities  launcher icons can wind up looking fuzzy because the launcher app has to upscale a lower-resolution icon for display  To avoid these display issues  apps should use the mipmap  resource folders for launcher icons  The Android system preserves these resources regardless of density stripping  and ensures that launcher apps can pick icons with the best resolution for display     from http   developer android com tools projects index html mipmap

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If you build an APK for a target screen resolution like HDPI  the Android asset packageing tool AAPT can strip out the drawables for other resolution you don   t need But if it   s in the mipmap folder then these assets will stay in the APK  regardless of the target resolution

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The Android implementation of mipmaps in 4 3 is exactly the technique from 1983 explained in the Wikipedia article        Each bitmap image of the mipmap set is a downsized duplicate of the   main texture  but at a certain reduced level of detail  Although the   main texture would still be used when the view is sufficient to render   it in full detail  the renderer will switch to a suitable mipmap image         when the texture is viewed from a distance or at a small size    Although this is described as a technique for 3D graphics  as it mentions  viewing from a distance    it applies just as well to 2D  translated as  drawn is a smaller space   i e   downscaled     For a concrete Android example  imagine you have a View with a certain background drawable  in particular  a BitmapDrawable   You now use an animation to scale it to 0 15 of its original size  Normally  this would require downscaling the background bitmap for each frame  This  extreme  downscaling  however  may produce visual artifacts   You can  however  provide a mipmap  which means that the image is already pre-rendered for a few specific scales  let s say 1 0  0 5  and 0 25   Whenever the animation  crosses  the 0 5 threshold  instead of continuing to downscale the original  1 0-sized image  it will switch to the 0 5 image and downscale it  which should provide a better result  And so forth as the animation continues   This is a bit theoretical  since it s actually done by the renderer  According to the source of the Bitmap class  it s just a hint  and the renderer may or may not honor it          Set a hint for the renderer responsible for drawing this bitmap    indicating that it should attempt to use mipmaps when this bitmap    is drawn scaled down        If you know that you are going to draw this bitmap at less than    50  of its original size  you may be able to obtain a higher    quality by turning this property on         Note that if the renderer respects this hint it might have to    allocate extra memory to hold the mipmap levels for this bitmap        This property is only a suggestion that can be ignored by the    renderer  It is not guaranteed to have any effect         param hasMipMap indicates whether the renderer should attempt                     to use mipmaps        see  hasMipMap       public final void setHasMipMap boolean hasMipMap        nativeSetHasMipMap mNativeBitmap  hasMipMap       I m not quite sure why this would be especially suitable for application icons  though  Although Android on tablets  as well as some launchers  e g  GEL   request an icon  one density higher  to show it bigger  this is supposed to be done using the regular mechanism  i e  drawable-xxxhdpi   amp c

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How are these mipmap images different from the other familiar drawable images    Here is my two cents in trying to explain the difference  There are two cases you deal with when working with images in Android    You want to load an image for your device density and you are going to use it  as is   without changing its actual size  In this case you should work with drawables and Android will give you the best fitting image  You want to load an image for your device density  but this image is going to be scaled up or down  For instance this is needed when you want to show a bigger launcher icon  or you have an animation  which increases image s size  In such cases  to ensure best image quality  you should put your image into mipmap folder  What Android will do is  it will try to pick up the image from a higher density bucket instead of scaling it up  This will increase sharpness  quality  of the image    Thus  the rule of thumb to decide where to put your image into would be    Launcher icons always go into mipmap folder  Images  which are often scaled up  or extremely scaled down  and whose quality is critical for the app  go into mipmap folder as well  All other images are usual drawables

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There are two distinct uses of mipmaps    For launcher icons when building density specific APKs  Some developers build separate APKs for every density  to keep the APK size down  However some launchers  shipped with some devices  or available on the Play Store  use larger icon sizes than the standard 48dp  Launchers use getDrawableForDensity and scale down if needed  rather than up  so the icons are high quality  For example on an hdpi tablet the launcher might load the xhdpi icon  By placing your launcher icon in the mipmap-xhdpi directory  it will not be stripped the way a drawable-xhdpi directory is when building an APK for hdpi devices  If you re building a single APK for all devices  then this doesn t really matter as the launcher can access the drawable resources for the desired density  The actual mipmap API from 4 3  I haven t used this and am not familiar with it  It s not used by the Android Open Source Project launchers and I m not aware of any other launcher using

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When building separate apks for different densities  drawable folders for other densities get stripped  This will make the icons appear blurry in devices that use launcher icons of higher density  Since  mipmap folders do not get stripped  it   s always best to use them for including the launcher icons

[android] Mipmap drawables for icons

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