What are the use cases for defining distances in a web layout for pixels and percentages?
Is there any downside to using pixels with respect to multiple resolutions? Will they scale correctly?
Percentage layout
This is generally referred to as fluid layout. Your elements will take a defined percentage of the total space available to them. This available space is determined by the element's parent.
When using percentage layouts, it's a good idea to specify a min-width and max-width on your design so that it remains usable at very low and high resolutions.
Pros
Scales with screen size, therefore get to use more space if it's available.
Cons
Makes it more difficult to know the exact position of something on screen. As a result, it can make creating precise layouts more difficult.
Can lead to unexpected layouts if child elements are fixed width (i.e. an image) and end up being larger than their fluid width parent.
Pixel layout
This is usually known as fixed layout. Your element will always be the same defined pixel size and will not take available parent space into account.
Pros
Always know an element's exact size.
Creating precise layout is easier.
Cons
You don't scale with resolutions. Your layout will always be the same width, making for wasted space when people have high resolutions.
I'll reply to this one by telling you a true story.
We had a client which wanted a map view, made up of divs.
Suddenly, he decided he wanted zooming as well.
I had to change all those fine-grained pixel positions to percentages.
Causing the wrapping div to change width/height (in pixels) relatively, we got a nice and reasonable zooming effect.
NB: During design phase, I quickly drew up a prototype, I'm going to look it up for you...
Edit: Nope, nothing found, sorry.
For percentages you have to have a base value, so it would be something like an image that has a size set outside of the CSS, if you just use a percentage on a DIV, for example, it wouldn't have anything to base that off of except the actual size it was by its being filled with text, for example, so it would not be practical to use percentages as a way to size it as it would rarely produce the desired output, if you are re-sizing something with a pixel size, such as by using javascript, you could resize by a percentage that would resize the original value (in pixels)
They do different things.
Pixel values always relate to hypothetical pixels on the output device.
Percent values relate to the computed size of the containing block (for block elements) or the containing block's font size (for font sizes).
Em and pt values relate to the current font size.
If you want your item to scale with its container, use percentages. If you want it to scale with font size, use ems. If you don't want it to scale at all, use pixels.
And then there's IE6; whoever 'implemented' CSS in that thing obviously had no idea what the various CSS properties were supposed to do.
Be careful using percentages, webkit browsers don't calculate percentages correctly. It's all because webkit doesn't calculate subpixels correct.
Detailed information about this issue can be read here: Percentage bugs in webkit
I would recommend you to always use pixels to don't have any layout dimensions differences between browsers.
Related
Just a straight forward question. I´m trying to make the best possible choice here and there is too much information for a "semi-beginner" like me.
Well, at this point, I´m trying with screen size values for my layout (activity_main.xml (normal, large, small)) and with different densities (xhdpi, xxhdpi, mhdpi) and, if a can say so myself, it is a mess. Do I have to create every possible option to support all screen sizes and densities? Or am I doing something really wrong here? what is the best approach for this?
My layouts are now activity_main(normal_land_xxhdpi) and I have serious doubts about it.
I´m using last version of android studio of course. My app is a single activity with buttons, textview and others. Does not have any fragments or intents whatsoever, and for that reason I think this has to be an easy task, but not for me.
Hope you guys can help. I don't think i need to put any code here, but if needed, i can add it.
If you want to make a responsive UI for every device you need to learn about some things first:
-Difference between PX, DP:
https://developer.android.com/training/multiscreen/screendensities
Here you can understand that dp is a standard measure which android uses to calculate how much pixels, lets say a line, should have to keep the proportions between different screensizes with different densities.
-Resolution, Density and Ratio:
The resolution is how much pixels a screen has over height and width. This pixels can be smaller or bigger, so for instance, if you have a screen A with 10x10 px whose pixels are two times smaller than other screen B with 10 x 10 pixels too, A is two times smaller than B even when both have 10 x 10 px.
For that reason exists the meaning Density, which is how much pixels your screen has for every inch, so you can measure the quality of a screen where most pixels per inch (ppi) is better.
Ratio tells you how much pixels are for height as well as width, for example the ratio of a screen of 1000 x 2000 px is 1:2, a full hd screen of 1920 x 1080 is 16:9 (16 pixels height for every 9 pixels width). A 1:1 ratio is a square screen.
-Standard device's resolutions
You can find the most common measurements on...
https://material.io/resources/devices/
When making a UI, you use the DP measurements. You will realize that even when resolution between screens are different, the DP is the same cause they have different densities.
Now, the right way is going with constraint layout using dp measures to put your views on screen, with correct constraints the content will adapt to other screen sizes
Anyway, you will need to make additional XML for some cases:
-Different orientation
-Different ratio
-Different DP resolution (not px)
For every activity, you need to provide a portrait and landscape design. If other device has different ratio, maybe you will need to adjust the height or width due to the proportions of the screens aren't the same. Finally, even if the ratio is the same, the DP resolution could be different, maybe you designed an activity for a 640x360dp and other device has 853x480dp, which means you will have more vertical space.
You can read more here:
https://developer.android.com/training/multiscreen/screensizes
And learn how to use constraintLayout correctly:
https://developer.android.com/training/constraint-layout?hl=es-419
Note:
Maybe it seems to be so much work for every activity, but you make the first design and then you just need to copy the design to other xml with some qualifiers and change the dp values to adjust the views as you wants (without making from scratch) which is really faster.
For representing most popular artists from EchoNest API, I've been trying to set-up Silverlight Toolkit's TreeMap using images, their TreeItemDefinition.ValueBinding being defined as the area of the image.
While it mostly fills up the space when the image stretch is set to 'Fill' :
When setting image stretch to 'Uniform' a lot of blank spaces remain :
On this post, image carving is suggested : Treemapping with a given aspect ratio
How can I know which images should be carved and at what dimensions they should be carved if possible at all ?
Is this problem solvable without human intervention for a good result ?
I don't think there is a way to know which images should be carved and at what dimensions they should be carved. An ok-ish euristic might be to check if the mean energy of an image is > a certain threshold (this can be refined to check only blocks of every image, and combining the result later: if the image has blocks without details/energy, it can be carved, at least in that section).
What i think would be better is to apply seam carving to the already composed image: that will try to carve out the white outlines (adding "artificial" energy to the patches of images might lead to even better results, preserving more the shapes of each image). This paper might be of use to check out other image resizing methods too.
I have a barcode image. I have to make it smaller.
Can that damage the barcode?
Proportional scaling
Not proportional scaling (only height changes)
Barcodes are: Type UPC-A / EAN-13 "vertical lines". Sorry not an expert in barcodes, thought the type of barcode would not be important. Scaling is moderate, the image does not lose relevant data.
Regular barcode (=vertical stripes) is recognized by the relative width of the lines. Thus, the horizontal height only matters for robustness against diagonal scanning. If the codes are scanned with a hand scanner, I'd just scale the height (or crop the image). In any case, the different widths of the lines should still be clearly visible. There may be compliance rules suggesting minimum proportions for a given barcode standard.
For regular linear product barcodes, the simple answer is yes, you can scale it (both case are safe).
However, if you scale too far and the bars end up too close together, you will start to get a high level of read errors.
You'll need to test it with an appropriate barcode reader to make sure you haven't scaled too much.
When scaling a barcode, there are several things you must keep in mind.
1) You get the absolute sharpest edges in a barcode if each module (the narrowest bar) is a whole number of pixels wide.
2) If the module width is not a whole number of pixels, produce a barcode where the width of each module is the truncated whole number and use bilinear interpolation to scale up. This will give you at most one pixel of gradient at the edges.
3) Be careful when buying a barcode library, choose one that includes built-in scaling that preserves the barcode, such as this one or this one. Barcodes have special demands that image processing normally does not have, such as pixel-perfection. Using e.g. Gimp might damage the barcode.
i'm working in a project to recognize a bit code from an image like this, where black rectangle represents 0 bit, and white (white space, not visible) 1 bit.
Somebody have any idea to process the image in order to extract this informations? My project is written in java, but any solution is accepted.
thanks all for support.
I'm not an expert in image processing, I try to apply Edge Detection using Canny Edge Detector Implementation, free java implementation find here. I used this complete image [http://img257.imageshack.us/img257/5323/colorimg.png], reduce it (scale factor = 0.4) to have fast processing and this is the result [http://img222.imageshack.us/img222/8255/colorimgout.png]. Now, how i can decode white rectangle with 0 bit value, and no rectangle with 1?
The image have 10 line X 16 columns. I don't use python, but i can try to convert it to Java.
Many thanks to support.
This is recognising good old OMR (optical mark recognition).
The solution varies depending on the quality and consistency of the data you get, so noise is important.
Using an image processing library will clearly help.
Simple case: No skew in the image and no stretch or shrinkage
Create a horizontal and vertical profile of the image. i.e. sum up values in all columns and all rows and store in arrays. for an image of MxN (width x height) you will have M cells in horizontal profile and N cells in vertical profile.
Use a thresholding to find out which cells are white (empty) and which are black. This assumes you will get at least a couple of entries in each row or column. So black cells will define a location of interest (where you will expect the marks).
Based on this, you can define in lozenges in the form and you get coordinates of lozenges (rectangles where you have marks) and then you just add up pixel values in each lozenge and based on the number, you can define if it has mark or not.
Case 2: Skew (slant in the image)
Use fourier (FFT) to find the slant value and then transform it.
Case 3: Stretch or shrink
Pretty much the same as 1 but noise is higher and reliability less.
Aliostad has made some good comments.
This is OMR and you will find it much easier to get good consistent results with a good image processing library. www.leptonica.com is a free open source 'C' library that would be a very good place to start. It could process the skew and thresholding tasks for you. Thresholding to B/W would be a good start.
Another option would be IEvolution - http://www.hi-components.com/nievolution.asp for .NET.
To be successful you will need some type of reference / registration marks to allow for skew and stretch especially if you are using document scanning or capturing from a camera image.
I am not familiar with Java, but in Python, you can use the imaging library to open the image. Then load the height and the widths, and segment the image into a grid accordingly, by Height/Rows and Width/Cols. Then, just look for black pixels in those regions, or whatever color PIL registers that black to be. This obviously relies on the grid like nature of the data.
Edit:
Doing Edge Detection may also be Fruitful. First apply an edge detection method like something from wikipedia. I have used the one found at archive.alwaysmovefast.com/basic-edge-detection-in-python.html. Then convert any grayscale value less than 180 (if you want the boxes darker just increase this value) into black and otherwise make it completely white. Then create bounding boxes, lines where the pixels are all white. If data isn't terribly skewed, then this should work pretty well, otherwise you may need to do more work. See here for the results: http://imm.io/2BLd
Edit2:
Denis, how large is your dataset and how large are the images? If you have thousands of these images, then it is not feasible to manually remove the borders (the red background and yellow bars). I think this is important to know before proceeding. Also, I think the prewitt edge detection may prove more useful in this case, since there appears to be less noise:
The previous method of segmenting may be applied, if you do preprocess to bin in the following manner, in which case you need only count the number of black or white pixels and threshold after some training samples.
I need the user to set a number of percentage values which should always add up to 100%. What are standard ways to archieve this? I came up with the following:
1) have a standard slider control for each value you need to set. Moving one slider will automatically adjust all the others so the sum will always come out as 100%. You can fix inidividual sliders with a checkbox displayed next to it. Only the remaining, "free", sliders will be adjustable.
Pro: consists entirely of standard widgets users already know
Con: lots of widgets, lots of screen real estate used, looks ugly when you have lots of sliders and thus low percentage values, normalization to 100% isn't immediately obvious.
2) have a slider control with several sliding knobs.
Pro: normalization is implicit and obvious because the length of the slider is fixed, relative weight is easy to see at a glance
Con: non-standard, knobs can easily overlap each other, knobs aren't easy to fix, no obvious place to put a text/number representation for each interval/percentage
3) display a standard pie chart.
Pro: normalization is implicit and obvious, relative weight is easy to see
Con: non-standard for interactive use, hard to make intuitive slice resizing work, no place to put a text/number representation for each slice
4) ... ?
I'm not happy with either of these hence my question here. Any better ideas? I'm dealing with 3-10 individual percentage values on a rich windows client (i.e. not web).
cheers,
Sören
What about vertical sliders? Like a sound mixer. I think it looks a lot better than a list of 10 horizontal sliders.
Or fixed width bar with several sliders on them, a bit like the gradient control of Photoshop if you know it.
Similar to the timeline idea, how about a slider like the partitioning interface in GParted or similar disk partitioning tools?
You could display the percentage values and actual numbers above the dynamically resizing bars to allow the user to edit them numerically instead of using the sliders if they want to configure it manually.
How about a time line view; (gantt chart) kind of like in Microsoft Expression Blend or in flash where you have multiple layers for each action and each action can be within a range on the scale from 0 to 100.