I have to link a date and a name to some jpegs that I am including in my bundle, or possibly downloading from my own server to the Documents folder. Is there a way to extract EXIF data easily?
If so, then I will use EXIF to store this info. If not, then I will have to create a database or flat file that maps my extra data to the image file.
Keep in mind, these are not photos the iPhone has taken and is providing via UIImagePicker or from outside the sandbox. These are photos that I am including with the app or downloadig to the Docs folder myself. The important point here is ease:
Is it easier to
read EXIF file from my image files
have another file that keeps track of
the image file and the associated
data (could be sqlite)
Thanks!
You can try using iphone-exif toolkit to extract the data. However, it's licensed GPL and if your app is commercial you'll need to negotiate a license deal. If that's not viable then you may want to go the external meta-data route.
The actual EXIF data is stored in the form of a small TIFF file with EXIF-specific TIFF tags for information that doesn't have a home in the TIFF specification. When placed in a JPEG file (really a JFIF bitstream), it is stored in a JPEG APP1 marker which limits the total size of the EXIF data to just a bit less than 64KB.
It shouldn't be that difficult to locate the APP1 marker, confirm it contains EXIF data, and then parse out a specific collection of EXIF tags with fairly brute force coding.
One example you can look at is exiftool which does just that, and is written in Perl and open source under the same terms as Perl itself.
If these files are purely for use in your own application and will not be reused in other tools by the user, then there is some mileage in storing your data as XML/JSON in the comment segment 0xFFFE. As mentioned before you get just short of 64k to play with.
The beauty of using the comment segment is that it should be preserved by image editing tools, is quick to access (because you do not need to traverse the IFD blocks that store EXIF data, you just read/write a text string with 4 byte type/length header) and is human readable/writable in a graphics app.
I would avoid storing the associated data in a db if practical, so that you don't risk the db becoming out of sync with the available files.
I use ExifTool
embedded in my app. Works a treat.
Related
First, thanks for any and all help regarding this topic.
Sites like Facebook and Twitter strip EXIF information from images as they are uploading. My goal is to allow users to upload images to our platform (working with Nextcloud and others) with full EXIF information, however, we need to display images that do not contain EXIF information or any metadata. Without stripping and creating a second, Exif-Free image for each, is it possible to simply hide that EXIF info so that, if a user downloads that image, the EXIF is not embedded?
We were told that the only way to do this is to have a second, exif-free copy (the order of when that's created is irrelevant pre/during/post upload). I'm hoping there's a way that we can simply display such a copy without doubling our physical space requirements.
Thanks again for your help.
Exif is metadata, along with IPTC, XMP, AFCP, ICC, FPXR, MPF, JPS and a comment, just for the JFIF/JPEG file format alone. Other picture file formats support even more/other metadata.
You wrote it yourself: a download - so it's a file in any case. Pictures are files, just like executables, movies, texts, music and archives are files, too. And metadata is part of its content, so whoever accesses the raw bytes of the file can grab everything in it. Which is not "please don't look" proof. If you
create that on the fly by stripping metadata everytime a download is requested,
or if you do it once to preserve performance and instead occupy space remains your decision.
If there would be something as simple as a "don't show" feature then it would still be in the file and could be extracted easily by software written to ignore that instruction. Seriously, there's no shortcut to that - do it properly and don't spare yourself from getting work done at the wrong end.
How is fireworks able to store this extra information in a format that is otherwise flat raster. And is there any open source way to write similar vector, layered, paginated files in Png format that would be readable by fireworks?
The PNG format allows for ancillary data chunks to store metadata aside from the image itself. I don't believe anyone's actually worked out the format that Adobe stores that data in though.
I find many similar question but i didn't get solution for this.
Is it possible to upload some file like image, document, zip file to upload on iCloud programmatically?
See table 4-1 in the documentation:
How do you manage the data? Manage files and directores using the
NSFileManager class. Open, close, read, and write files using standard
file system routines.
So if you can create a file, you can store it in iCloud. But remember there's a finite, relatively small amount of space available.
iCloud can handle all kinds of files. So if you want rot use an obscure file format or invent your own, go for it. It only can to be converted into a byte stream/NSData, but then again, what isn't?
Check this tutorial walkthrough app. It shows how to create, modify and delete files for iCloud.
http://github.com/lichtschlag/iCloudPlayground
here's the thing: I download a bunch of data in JSON format. I put that into an array of dictionaries. Then, I save to disk. One dictionary stores a link to some image. What I would like to do is to store also the actual image (not the link!) along with rest of the data. How would you start? Which way to go?
I would download the image and save the local path alongside the URL path.
However, if you're going for one big file, you could always base64-encode it.
I think using the filesystem directly and saving your local path would be more efficient and effective than one monolithic file, as you'll save a lot of parsing and encode/decode time.
I suggest you to start from this tutorial : SimpleFTPExample
My iPhone (actually, iPad) app creates documents that consist of several images, plus a bit of metadata. What's the best practice for storing these sorts of documents on disk? I see two main options:
Create a folder for each document, and store my images as separate PNG files within the folder (plus another little file for the metadata).
Create a single file which contains all images and metadata.
But I'm not sure how to easily do option 2. I think I can convert my images in PNG format to/from NSData, but then what? I'm still a newbie at Cocoa, but I believe I saw something about stuffing mixed data into some NSSomethingOrOther and having this write itself out to disk, and read itself back in later. Does this ring a bell with anyone? And, will it work with large binary blobs of data like my images?
Or would you recommend I simply go with option 1?
Simply go with option1. It's clean, elegant, and simple to implement. You could even use (a subset of) HTML.
TIFFs and PDFs can have multiple pages.
Creating a document centric iPhone/iPad application with own file format using ZipArchive