I am trying resize a UIImage and keep the original EXIF metadata.
However, it looks like no straight forward method available now.
I tried CGImageSourceCopyPropertiesAtIndex to get original EXIF metadata but I have no idea how can I write it into target image.
However, i've notice that ALAsset library function have related stuff like writeVideoAtPathToSavedPhotosAlbum, but I wonder if that would be helpful for my resize requirement ..
Any clue ?
Related
Problem
I'm posting images to a server, but when I pull them back to the device, they turn sideways.
My thoughts are the Exif data attached to the image are telling the server how to orient the image.
How can I edit the exif data on a UIImage from the camera or library before its sent? I've seen solutions where they rotate the image when its returned but I want a solution for before its even posted.
A clue to what might be happening is that when the imageOrientation is posted it is normal, but return Up from the server no matter what. Does this possibly mean that the server is stripping the Exif data needed to determine the orientation?
Thank you.
[self.distanceSlider setThumbImage:[UIImage imageNamed:#"handle-slider"] forState:UIControlStateNormal];
Let's take a look at that code.
If I use retina display, will the image called be handle-slider#2x instead of handle-slider?
Notice that this could raise an issue. Imagined if I load an image for the sole purpose of processing it and I really really want to load handle-slider, or handle-slider#2x? Then having iOS to override my decision and arbitrarily load #2x image will be kind of silly.
On the other hand most of the time, I used UIImage imageNamed to populate a button. In that case, it makes perfect sense to add #2x.
In any case, which path does apple eventually use and if possible, what's the reference?
I searched stackOverflow.
Most answers are inconsistent with one suggesting one or the other.
The documentation for [UIImage imageNamed:] has exactly the information you want to know.
This method looks in the system caches for an image object with the
specified name and returns that object if it exists. If a matching
image object is not already in the cache, this method loads the image
data from the specified file, caches it, and then returns the
resulting object.
On a device running iOS 4 or later, the behavior is identical if the
device’s screen has a scale of 1.0. If the screen has a scale of 2.0,
this method first searches for an image file with the same filename
with an #2x suffix appended to it. For example, if the file’s name is
button, it first searches for button#2x. If it finds a 2x, it loads
that image and sets the scale property of the returned UIImage object
to 2.0. Otherwise, it loads the unmodified filename and sets the scale
property to 1.0.
I am looking for a way to, in Objective-C, create a PNG from several smaller PNGs based on how the user sets things up. Is this possible using existing Apple classes, or do I need to use a 3rd party library? If 3rd party code is needed, can anyone recommend a good library? The simpler the better - simple filters (such as darkening/lightening the image) would be nice but not required.
Here is some pseudo-code, to give you a better idea of what I am looking for:
image = [myImageLibrary imageWithHeight:1024 width:768];
[image addImage:#"background.png" atX:0 andY:0 withRotation:0];
[image addImage:#"image2.png" atX:100 andY:200 withRotation:90];
[image saveAtLocation:#"output.png"];
At output.png we see image2.png placed on top of background.png and rotated 90 degrees
P.S. - I am sorry if this seems to be a duplicate of another question, I just have not found an answer that works for what I am trying to do.
Have you read the "Creating and Drawing Images" section of the Drawing and Printing Guide for iOS and the UIImage Class Reference docs?
What you're after is perfectly possible - with a well built class you could pretty much use that pseudo code as-is.
As a starter for ten, you could:
Create your own graphics context via UIGraphicsBeginImageContext.
Draw into that via the drawAtPoint: method of the UIImage class
Save the resultant image data out via UIGraphicsGetImageFromCurrentImageContext.
In terms of steps 1 and 3, see the UIKit Function Reference for more info. Additionally, the imageWithCGImage:scale:orientation: method of the UIImage class may prove useful for performing transformations, etc. as a part of step 2.
You'll want to look at CGContextDrawImage to draw your images, using a custom bitmap context, and then save it out using UIGraphicsGetImageFromCurrentImageContext(). The rotation can be done by applying CGAffineTransforms to your CGContext.
More information on Core Graphics here:
http://developer.apple.com/library/mac/#documentation/GraphicsImaging/Conceptual/drawingwithquartz2d/Introduction/Introduction.html
I've tried some code from each of these questions:
How to make one color transparent on a UIImage?
How to mask a UIImage so that white becomes transparent on iphone?
but have come up unsuccessful, unfortunately working with Core Graphics and images is not my strong suit.
How would I go about accessing a UIImage's raw data and changing the white pixels to clear?
How would I go about accessing a UIImage's raw data …?
Look at the documentation.
You'll find that there is no way to get the raw data behind a UIImage. The closest you can get is a CGImage. That will let you get its data provider, which you can ask for a copy of the raw data.
The problem with that solution is that you need to handle every possible configuration (RGBA, ARGB, RGB_, _RGB, RGB, 8-bpc, 16-bpc, etc.) that CGImage supports. That's a lot of work. If you don't do it, then someday, you'll get surprised by an image that somehow doesn't work with your code, or by an OS upgrade changing how the CGImage gets created.
The CGImageCreateWithMaskingColors function, suggested on one of the other questions you linked to, is the correct solution.
One thing that's tripping you up is that the values shown in the accepted answer on that question are generally bogus: They're out of range. The Quartz 2D Programming Guide has more details in at least two.places.
I also argue against including that answer's createMask: method, since it doesn't do what it says it does and is barely useful at all (it's only worth having if the source image may be CMYK, but how likely is that on an iPhone app?). Skip it and create the mask image from the UIImage's CGImage directly.
That answer will probably work just fine once you fix those two problems.
I'm working with an NSImage which comes from a PDF. When I initially create the image, it has only one NSImageRep and that is NSPDFImageRep. This is good. I can work with it. I can find out how many pages it has, and go to a specified page, and draw it, etc.
The problem is that as soon as I turn my back, it gets turned into a NSCachedImageRep, which doesn't seem to have multiple pages. Now, if I keep the PDFImageRep in a separate variable, it is kept track of, but it isn't associated with the image anymore, so when I draw the image, it's still on the same page.
What am I missing?
thanks.
You need to call [image setDataRetained:YES] on the image, so that your original PDF data is kept around, otherwise it will be cached to a bitmap.
If you're still having problems you could turn off caching altogether by using [image setCacheMode:NSImageCacheNever].
Try it on 10.6. The problem has probably evaporated.
Please see the AppKit release notes for details of the NSImage changes.