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minimum pixels of the largest image's side to fit android xxhdpi screen

I'm making an android App that shows images at full screen.
I learned some about dpi and dp, but I didn't find how many pixel must be the largest side of my images (in prospective to good fit also in landscape mode) to appear good in different devices.
As in the documentation, the most used screen configurations are normal with hdpi, xhdpi and xxhdpi density:
So, if my thinking is correct, I can make only one image to fit the xxhdpi to works fine also with the other two densities, and put it in Android Studio under the "res/drawable" folder (without qualifier).
Specifying the image size in dp in the layout, Android should scale the image for the smaller configurations.
But, for the xxhdpi, how many pixel must be the largest side of my image, in pixel, to show good?
Edit: how many pixel must be the longest side of my image to be showed properly in a device with xxhdpi density without the image appearing grainy?
All images are photo, not icons, so I can't use the vector graphics.

By looking at the Android Documentation. One can estimate the size of the picture. look at below picture
So, your image resolution should be in similar resolution
LDPI: 200 X 320px
MDPI: 320 X 480px
HDPI: 480 X 800px
XHDPI: 720 X 1280px
XXHDPI: 960 X 1600px
XXXHDPI: 1440 x 2560px
A little bit of +/- won't affect the outcome because with these standard sizes the aspect ratio of any portrait picture should be respected.

Well, if you put the image which fits the xxxhdpi inside the folder drawable, then it will fit all the screens.
But there is another way to use only one image instead of using multiple images for different resolutions. It's by using svg images which are vector images that will not be affected by zoom in or zoom out.
To use svg you need to follow these instructions:
Make the icon to be icon.svg
In the Android Studio, right click on drawable folder
Choose New -> Vector Asset
Choose Local File (SVG, PSD)
Choose your svg file
Click Next and choose the name
Click Finish
In the app build.gradle add the following inside android block:
vectorDrawables {
useSupportLibrary true
}
In the xml layout file, add the following:
<AppCompatImageView
android:width="wrap_content"
android:height="wrap_content"
app:srcCompat="#drawable/your_svg_file"
/>

Android have ratios defined for a image to set in all different drawables
Android icons require five separate sizes for different screen pixel densities. Icons for lower resolution are created automatically from the baseline.
mdpi: 160 dpi 1×
hdpi: 240 dpi 1.5×
xhdpi: 320 dpi 2×
xxhdpi: 480 dpi 3×
xxxhdpi:640 dpi 4×
Above size is for normal pixel icons. There are fix android size for Action bar, Dialog & Tab icons, Launcher icons & Notification icons
Check this link for more details http://iconhandbook.co.uk/reference/chart/android/

You have to take a look at the current market of smartphones.
Here you can see the screen sizes and resolutions of the most popular devices in the market.
http://screensiz.es/
Order the list in pixel per inch and you will see that top smartphones have resolutions bigger than 500 ppi or another way to see it, much bigger than 72ppi of your images.
If you have enough space to store or mechanism to download images try to test with full quality. If thats too much try to find a compromise. Lower image quality and see the result in high resolution screen.
Note that you didn't posted here the total size of image, in case is bigger than screen size, take a look at total size of image and compress it to fit your needs, maintaining as much as possible the resolution.
Edit: Looking only to size of image in pixels, the current biggest screen in smartphone is 2560 x 1440 pixels, so you wont need any image bigger than this.

If I understand your answer correctly, you are talking about images (pictures of lovely cats and dogs?) and not about icons?
I prefer putting images into the nodpi folder.
nodpi Resources for all densities. These are density-independent
resources. The system does not scale resources tagged with this
qualifier, regardless of the current screen's density.
Afterwards I would create a fullscreen ImageView and let imageView do the scaling if needed

Different sizes of images in Android

I'm trying to create main activity in my application using GridView. I need to have a grid 3x3. Every cell contains ImageView (icons for different actions). All images must have the same size. And my question is: what sizes of image I must use? I watched tutorial and found a table with sizes for different resolutions and density. But I didn't understand. For instance, I have mdpi density and screen size 480*800. Does it mean that I should use icons 160*266 for this screen? And what sizes should be for other densities and screen sizes? How can I calculate them?

This is one of the most asked question, you can search for more details, but let me give you briefly how it works.
MDPI is considered as the base line and following are the scales
MDPI - X1
HDPI - X1.5
XHDPI - X2
XXHDPI - X3
XXXHDPI - X4
Now you must be thinking what is this.
Since you want to have 3X3 grid with cell of equal size, you can consider the following.
In general mdpi screen size is 360 X 640, so each image size will be 120dp X 212dp Approx.
For mdpi screen, your Image size should be 120px X 212px
For hdpi screen, your Image size should be 180px X 318px
For xhdpi screen, your Image size should be 240px X 424px
For xxdpi screen, your Image size should be 360px X 636px
For xxxdpi screen, your Image size should be 480px X 848px
Now where you should place these images?
Project -> app -> src -> main -> res
Here, create folders with name drawable-mdpi, drawable-hdpi, etc, and place respective images in these folders.
Thats it for supporting multiple screen densities.
According to docs, MDPI and HDPI screen sizes are given considering
their aspect ratio to 3:4, but since most of the users have HD
devices with aspect ratio of 9:16, you can consider the most standard
screen size in Market i.e. 1080 X 1920 which corresponds to XXHDPI and
acts as baseline to make the assumption of considering MDPI to be 360
X 640. For high quality apps, trade off has to be made for lower
devices since most of the existing users have XXHDPI or higher
devices.

Android tab emulator blurs images, pls suggest

I'm trying to develop for an android tab with the resolution of 1280x720. But when I place an image, say 1000x500, into the xml view it appears almost two times smaller. When I change its height and width from wrap_content to 1000px and 500px, it looks ok in xml, but when I launch it in the emulator, it gets very blurry, as if it would be at first scaled down and then expanded again.
Any ideas?
Thanks!

Put the drawables for tablet in the drawable-xlarge folder and the problem may dissapear.
Maybe your problems is that the most tablets have xlarge screens and mdpi screen density and you put the drawables in the hdpi folder.
For more info see this page.

Try using "dp" instead of pixels. Also place the drawable in the density specific folder. between ldpi and hdpi the size in pixels need to be twice for them to show up as of same size on the device. For example a launcher icon on ldpi device is 36 x 36px while on hdpi it is 72 x 72 px
Use same ratio to create your image in higher resolution with larger size.

Android screen sizes in Pixels for ldpi, mdpi, hpdi?

I've read 10 articles yet still cant find any relation between ldpi, mdpi, hdpi and the actual dimensions in pixels!? Can anybody give a straightforward answer please(if there is one!)
I'm basically trying to put together a splash screen that needs to work on multiple devices without stretching - but i'm struggling as everything I try is either squashed or stretched!?
Cheers
Paul

The ldpi, mdpi and hdpi refer to screen density, which means how much pixels can fit into a single inch.
the ratio in pixels between them is:
ldpi = 1:0.75
mdpi = 1:1
hdpi = 1:1.5
xhdpi = 1:2
xxhdpi = 1:3
xxxhdpi = 1:4
so lets take an image with about the size of 100X100:
for mdpi it should be 100X100
for ldpi it should be 75X75
for hdpi it should be 150X150
for xhdpi it should be 200X200
for xxhdpi it should be 300X300
for xxxhdpi it should be 400X400
this way, for screens with the same size but different DPI, all the images seem the same size on screen.
Also you have multiple screen size types small, normal, large, xlarge and each one of them can be ldpi, mdpi, hdpi, xhdpi, xxhdpi (Nexus 10) or xxxhdpi.
You can try to create a splash screen image that fit to each and every screen type
which gives you 4*5 = 20 different images (it seems to much for me).
For now only the Nexus 10 is at the xxhdpi category.

Install ImageMagick and use this shell script to generate your splash and icon files for multiple devices - iOS, Android, Bada and Windows Phone. You can use cygwin/gitbash if you are on Windows
I just did and I'm pretty happy with it :-)
The screen sizes are inside the script and are -
480x800 - screen-hdpi-portrait.png
320x200 - screen-ldpi-landscape.png
720x1280 - screen-xhdpi-portrait.png
320x480 - screen-mdpi-portrait.png
480x320 - screen-mdpi-landscape.png
200x320 - screen-ldpi-portrait.png
800x480 - screen-hdpi-landscape.png

The definitions are:
xlarge screens are at least 960dp x 720dp. large screens are at
least 640dp x 480dp. normal screens are at least 470dp x 320dp.
small screens are at least 426dp x 320dp. (Android does not currently
support screens smaller than this.)
Also, check out this blogpost from Dianne Hackborne:
http://android-developers.blogspot.com/2011/07/new-tools-for-managing-screen-sizes.html
Probably the easiest thing is to use an image view and set the scaletype to CENTER_CROP.
(Scale the image uniformly (maintain the image's aspect ratio) so that both dimensions (width and height) of the image will be equal to or larger than the corresponding dimension of the view).
Make sure that you use the src tag rather than setting the background.
<ImageView
android:id="#+id/home_video_layout"
android:src="#drawable/splash_image"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:scaleType="centerCrop"
/>
Updated:
Understanding Screen Densities and the “dp”
Resolution is the actual number of pixels available in the display, density is how many pixels appear within a constant area of the display, and size is the amount of physical space available for displaying your interface. These are interrelated: increase the resolution and density together, and size stays about the same. This is why the 320x480 screen on a G1 and 480x800 screen on a Droid are both the same screen size: the 480x800 screen has more pixels, but it is also higher density.
To remove the size/density calculations from the picture, the Android framework works wherever possible in terms of "dp" units, which are corrected for density. In medium-density ("mdpi") screens, which correspond to the original Android phones, physical pixels are identical to dp's; the devices’ dimensions are 320x480 in either scale. A more recent phone might have physical-pixel dimensions of 480x800 but be a high-density device. The conversion factor from hdpi to mdpi in this case is 1.5, so for a developer's purposes, the device is 320x533 in dp's.

I have found this online dip <--> pixels calculator very useful.
https://pixplicity.com/dp-px-converter/

I support previous answers but don't forget the power of Draw9Patch or using NinePatchDrawables

These refer to screen pixel density, not screen dimension. You need to look into screen size specifiers like small, medium, large, and xlarge instead if you really need to change behavior based on screen size in pixels.
The Android docs explain what densities and sizes match these identifiers.

Android devices can have different width-to-height ratios, while your image has a fixed one. If you do not want your image stretched, you will have to fill the blank spaces above and below or left and right.

Android: Multiple Image Density support - scale height width and dpi?

I have an android app that I'm trying to add support for different densities, screen sizes, etc. I've developed the app on the simulator with the HVGA support and used all icons from our iphone app which turns out nice since the resolution was at 320x480. Everything looks good now but I'm a bit confused after reading the official android documentation. For layouts I'm going through and ensuring everything is in dp units but when it comes to the images I'm lost. I know that mdpi is 160 but what do I tell my designer for what the hdpi image needs to be? Do we need to increase the height and width and the dpi? Or is it simply enough to leave the dpi as is and increase the height width? For example, if I have an image that's 100 x 100 with 160 dpi, in order to render it identical on an hdpi screen it should now be 150 x 150 with 240 dpi? Assuming if I leave the dpi at 160 it will just be a little blurred? Sorry about silly question but I just want to make sure I'm doing everything right and I'm really a C developer with no graphics experience at all.... No excuse at all but could use some help. I saw some examples where the splash screen for mdpi was 320x480 at 160 dpi but then the hdpi splash screen was at 480 x 800 at 240. Obviously 480 x 1.5 does not equal 800. Furthermore, after looking at the icons in the android sdk, they only scale up the width and height, not the dpi. Probably because they're icons and don't need to be? Lost in photoshop land....

For me as a Graphic Artist of a Mobile Development Company, I made UI's for Android in this dimension:
HDPI : 640px x 960px in 300dpi optimized by 75%
MDPI : 640px x 960px in 300dpi optimized by 50%
LDPI : 640px x 960px in 300dpi optimized by 25%

Take a look at Providing Resources.
There is a section there on "Screen pixel density (dpi)". You are correct that you just scale your width and height for the resources. A 90 pixel image at ldpi becomes a 120 px a mdpi, a 180 at hdpi and a 240 ad xhdpi.
You are also right that the 800 isn't 1.5 x the base 480 height. The reason for that is that these are all approximates based on targets for each density. The phone os lies to the applications running on it about its actual height and width and scales the resources to match the exact dimensions of the handset, since it can vary. This is my understanding.

I recently solved this problem by generating many PNGs of different sizes from a SVG vector image. These are the ratios I used for screen pixel densities and screen sizes:
ldpi:mdpi:hdpi:xhdpi:xxhdpi <-> 3:4:6:8:12
sw320dp:sw360dp:sw480d:sw600dp:sw720dp <-> 8:9:12:15:18
Putting these two together can give a 5 by 5 table of image size ratios that you need in make your image resources look great on most Android devices' screens. Of course, the downside is that many images will be generated, and the size of your APK will grow.
Please see http://aleakymemory.blogspot.com/2013/11/a-different-look-at-managing-android.html for the table of image size ratios.

Everything looks good now but I'm a bit confused after reading the official android documentation.
Which documentation did you read? Here are some to be going on with:
Supporting Multiple Screens
Icon Design