I used CGImageGetDataProvider and CGDataProviderCopyData and then get a pointer to the data. The first image I tested was a bmp and this method worked great. However, I changed my image to a JPG because I had read something about the Data Provider possibly being relative to the type of image. The length of that data returned indicates that it is 4 when it should be some large number representing the rows and columns of the image.
What I need is I can ask for the Data Provider to be for a bitmap so I can walk through the data uncompressed?
The data you get out of the data provider will be the data that went into creating the image. For instance, if the image was created using CGImageCreateWithJPEGDataProvider, it would be JPEG data. If you want bitmap data, you will need to make a bitmap, perhaps using CGBitmapContextCreate, and draw the image into the bitmap.
Related
I am trying to understand the basics behind Pixbuf and its factory methods new_from_data and new_from_stream.
new_from_data requires a string of bytes containing the image data, and other information such as bits per sample, with and height of image.
What I don't understand is why new_from_stream does not require those additional image information. Then, how can the Pixbuf know how to render the image new_from_stream does not provide any additional information other than the Gio.InputStream ?
new_from_stream() expects to get a stream of a supported image file, equivalent to new_from_file(). All the image formats contain metadata like height and width.
new_from_data() on the other hand expects a pixel buffer, which is essentially just an array of pixels without any metadata.
I would like to know how to load first a low quality UIImage and then load the original UIImage in high quality. Does it have an algorithm to do this in objective-c? I checked it out the class NYXImagesKit but it only works with iOS 5+ because it uses Core Image framework...And i need to work this with iOS 4.3+. Its effect is like Facebook app does.
JUST A edit:
check this out :
http://www.codinghorror.com/blog/2005/12/progressive-image-rendering.html
i want to do the Effect number 2
From the docs:
Incrementally Loading an Image
If you have a very large image, or are loading image data over the web, you may want to create an incremental image source so that you can draw the image data as you accumulate it. You need to perform the following tasks to load an image incrementally from a CFData object:
Create the CFData object for accumulating the image data.
Create an incremental image source by calling the function CGImageSourceCreateIncremental.
Add image data to the CFData object.
Call the function CGImageSourceUpdateData, passing the CFData object and a Boolean value (bool data type) that specifies whether the data parameter contains the entire image, or just partial image data. In any case, the data parameter must contain all the image file data accumulated up to that point.
If you have accumulated enough image data, create an image by calling CGImageSourceCreateImageAtIndex, draw the partial image, and then release it.
Check to see if you have all the data for an image by calling the function CGImageSourceGetStatusAtIndex. If the image is complete, this function returns kCGImageStatusComplete. If the image is not complete, repeat steps 3 and 4 until it is.
Release the incremental image source.
You can refer below link, it may be help you
uiimage-dsp
I want to read a .fits image of wide field sky and display the RGB values contained in a star. Can you please suggest a method to do so?
I have used fitsread to read in the image but i am not able to show the RGB values for specific locations(star).
In order to do this, you'll need a proper rgb fits file. The only .fits viewer I know of, ds9, does not support saving rgb fits files, but rather as the three separate (r,g,b) fits images. You can use "getpix" from wcstools (http://tdc-www.harvard.edu/wcstools/) or scisoft (http://www.eso.org/sci/software/scisoft/) on the individual frames. Note that "getpix" returns the pixel value given an image (x,y) location. ds9 does not provide the physical image location, but rather the wcs coordinates, so you may have to convert to image coordinates before calling getpix.
Which type of data is returned by the following function?
CFDataRef CreateDatafromImage(UIImage *image)
{
return CGDataProvidercopyData(CGImageGetDataProvider(image.CGImage));
}
Binary image data
Raw pixel data
Compressed image data
ASCII image data
I guess the closest answer would be 2) Raw pixel data. Though, to be honest, I don't really see what the difference would be between Binary image data, and Raw pixel data. As for the third choice, Compressed image data, I suppose I could imagine how that could be referring to whether the NS/CFData object returned represents the compressed JPEG data (say, 100 KB) as it exists in the file, or whether it represents the data in its uncompressed form (say, 24 bit RGB, which might be 280 KB). In that case, I guess you could say that it represents the data in its "uncompressed" form.
But then, how exactly are you defining "compressed"? For example, say you have an image that is saved and has the following layout: 16 bits per pixel RGB, kCGImageAlphaNoneSkipFirst, like in the last example in this image:
Compared to the other layouts pictured, you could think of this layout as being "compressed" in some sense. (See Color Spaces and Bitmap Layout).
So, to sum up, by the time you've obtained a CGImageRef, the image is in a "native representation" that Quartz understands. The data returned from that method is the raw pixel data; the data isn't in "JPEG format", or "PNG format", or "TIFF format", etc. You can use the inquiry functions to gather information about what combination of image channels, alpha channels, and bit depth the image has: CGImageGetBitmapInfo(), CGImageGetBitsPerComponent(), CGImageGetBitsPerPixel(), etc.
Dealing with the image formats like JPEG, PNG, TIFF, etc. are abstracted into other APIs and types such as CGImageSourceRef, CGDataProviderRef, CGImageDestinationRef, and CGDataConsumerRef. See Moving Data Into Quartz 2D and Moving Data Out Of Quartz 2D.
Uh... A CFDataRef object?
The documentation is here: http://developer.apple.com/library/ios/#documentation/CoreFoundation/Reference/CFDataRef/Reference/reference.html
It's an object you can use as NSData or CFData interchangeably.
Internally a CFData is created (With the CGDataProvidercopyData) from the return value of the CGImageGetDataProvider call.
Good luck :)
It is covered in the docs (which is one of the first hits in Google).
This particular technical note covers it in detail.
http://developer.apple.com/library/mac/#qa/qa2007/qa1509.html
I'm trying to get the pixel information from an image and have got to the point where I have my void* data object which is a pointer to the image data.
What exactly is this object? I've tried iterating over it hoping that it's an array of pixel info but it doesn't seem to work.
I want to get the rgb values for each pixel.
It's a pointer to the bitmap data. If you're having trouble interpreting it, then the bitmap probably isn't in the format you think it's in (CoreGraphics does some conversions automatically on loading external bitmaps).
Check the bitmap format info with CGBitmapContextGetBitmapInfo().