I am trying to use PNG images as Toolbar icons. I am currently reading them with imread an set the corresponding CData value.
Now I have some images with transparency. There is no alpha channel (I found some threads with solutions for that), but I get some kind of "Simple Transparency". The imfread function returns "simple" for the Transparency field and a vector of values between 0 and 1 for the SimpleTransparencyData field.
I couldn't find any information about this transparency type neither in the Matlab help nor the internet. So I would like to know if it is possible to show the transparent image in the toolbar directly, or if not how to composite the transparent values with the toolbar's background color.
In summary you set the CData value to be a NaN to represent transparency.
See this article that I wrote on undocumentedmatlab.com which describes how to do it for uicontrols.
For a toolbar icon you modify the CData property in the same way - the primary difference is that you dont need to modify the backgroundcolor property.
I did a quick test on the only solution I could probably imagine and it really seems to work:
I forgot to mention, that I am using indexed PNG files for this. But this sort of transparency seems to imply this fact.
The indexed colors are ordered that the (partially) transparent colors are at the beginning of the table. The SimpleTransparencyData now specifies the transparency of each of the indexed colors. Non-transparent colors are left out, as there are more colors than transparency values.
With that additional information it is easy to composite a single background color with the image.
Related
I need to implement an image segmentation function in MATLAB based on the principles of the connected components algorithm, but with a few modifications. This is intended for very simple, 2D images, with a background color and some objects in different colors.
The idea is that, taking the image as a matrix, I provide a tool to select the background color (it will vary for every image). Then, when the value of the color of the background of the image is selected, I have to segment all the objects in the image, and the result should be a labeled matrix, of the same size of the image, with 0's for the background, and a different number for each object.
This is a graphic example of what I mean:
I understand the idea of how to do it, but I do not know how to implement it on MATLAB. For each pixel (matrix position) I should mark it as visited and then if the value corresponds to the one of the background, assign 0, if not, assign another value. The objects can be formed by different colors, so in the end, I need to segment groups of adjacent pixels, whatever their color is. Also I have to use 8-connectivity, in order to count the green object of the example image as only one object and not 4 different ones. And also, the objects should be counted from top to bottom, and from left to right.
Is there a simple way of doing this in MATLAB? I know the bwlabel function, but it works for binary images only, so I'd like to adapt it to my case.
once you know the background color, you can easily convert your image into a binary mask of the same size:
bw=img!=bg_color;
Once you have a binary mask you can call bwlavel with 8-connectivity argument as you suggested yourself.
Note: you might want to convert your color image from RGB representation to an indexed image using rgb2ind before processing.
I have some textures containing some transparency parts (a donut, for example, which would show a transparent center). What I want to do is fill the middle of the donut (or anything else) with a plain white, in code (I don't want to have a double of all my assets that need this tweak in one part of my game).
Is there a way to do this? Or do I really have to have 2 of each of my assets?
First it is possible to change a transparent texture to not-transparent, if it wasn't then graphic editors would be in trouble.
Solution 1 - Easy but takes repetitive editing by hand
The question you should be asking yourself is can you afford the transition at run time or would have two sets of textures be more efficient; from experience I find that the later tends to be more efficient.
Solution 2 - Extremely hard
You will need a shader that supports transparency and that it marks the sections that have to be shaded white. That is, it keeps track of which area will be later filled with white. It is implied that since your "donut" is already transparent on some parts then it already uses that texture that has an alpha, but you will have to write your own shader mask and be able to distinguish which is okay to fill white and which is not (fun problem here). What you need to do is find the condition in which that alpha no longer needs to be alpha and has to be white. Once the condition is met you can change the alpha of via the Color's alpha property. The only way I see you able to do this is if there is a pattern to the objects, so that you can apply some mathematical model to them and use that to find which area gets filled. If the objects are very different then the make two sets of textures starts to look more appealing.
Solution 3 - Medium with high re-use value
You could edit the textures to have two different colors, say pink and green. Green is the area that gets turned white and pink is always transparent. When green should not be white then it is transparent. You would have to edit your textures by hand as well.
I've converted a colored photo to black and white, and bolded the edges. Now i need to convert it back to its original color with the bolded edges. Is there any function in matlab which allows me to do so?
Once you remove the colour from an image, there is no possible way to automatically put it back. You're basically reducing a set of 16,777,216 colours to a set of 256 - on average each shade of grey has 65,536 equivalent colours, and without the original image there's no way to guess which it could be.
Now, if you were to take the bolded lines from your black-and-white image and paint them on top of the original coloured image, that might end up producing what you're looking for.
If what you are trying to do is to use some filter over the B/W image and then use that with the original color. I suggest you convert your image to a color space with Lightness channel that suits your needs (for example L*a*b* if you need the ligtness to be uniformly distributed regarding human recognition of differences) and apply your filter only over the Lightness channel.
im creating and app where user already have an image (with different objects) without colors, i have to check the object and then color with respected color with the touch on that objects. how should i do this. can anyone help me.
I would say that that is non-trivial. I can only give hints since I have not done such an app yet.
First, you need to convert the image into a CGImageRef, for example by doing [uiimage_object CGImage].
Next you need convert the CGImageRef into array of pixel colors. You can follow the tutorial at http://www.fiveminutes.eu/iphone-image-processing/ for sample code. But for your app you need to convert the array into two dimension based on image width and height.
Then, use the coordinate of the user touch to access the exact pixel color value from the array. Next you read off the color values of the surrounding pixels and determine if color is similar to the touched pixel or not (you might need to read some wikipedia articles etc on doing the color comparison). If the color is similar, change the color to the one you want. Recurse until the surrounding color is different (i.e. you hit the boundary).
When you are finished modifying the pixel color value array, you need to convert the array back into CGImageRef using CGImageCreate function. Then you convert back to UIImage using [UIImage imageWithCGImage:imageref].
Now you are on your own to implement the steps into code. It would be unreasonable if you expect me to code all that for you, wouldn't it?
I need to place labels with a transparent background over a variable-content UIImage. Readability will vary significantly depending on the relationship between the color of the label's text and the color/luminosity of the area of the image displayed under the label. Since the image will be constantly changing, the color of the label's text needs to change in sync.
I have found several techniques for determining the color, perceived luminosity etc of a single pixel. However, I need to rather quickly (while a view loads) determine the rough perceived color/luminosity of an area of the UIImage under the frame of the UILabel. I presume I will also need to measure the alpha because the same color/luminosity looks different at different alpha values.
Is there a way to calculate such a value for an area? Will I be reduced to simply summing pixels? If it comes to that, is there an algorithm to accomplish this?
I've thought of two possible approaches:
Perform some "folding" operations i.e. combining pixels from one half of the area to the other half. Then repeat until I get a single value. Would this be practical? How would you logically combine pixels to average their perceived color/luminosity?
Sample a statistically significant number of pixels in the area and then combine them (somehow) to get a rough measure.
I think this problem comes up a lot these days with people being so found of customizing backgrounds. Seems like something that would be worth my time to bang out a category or class to handle this and then share it around.
What about simply outlining your text in a way that it will show on both dark and light backgrounds?
This is how it is handled in other situations where text must be displayed over a background with unknown content (for example, films with subtitles).