I wanted to know if I would be able to decompress a png with png++ and be able to get an access to the pixels with a file pointer and store them in a 2d or a 3d array and represent them in a hex format as the final result like a hex editor would. If not could anybody please suggest me a way I can do the same .
Intended language : c++
platform : linux.
Thanks in advance .
use fread to get the values but you should know how the header is stored how many bytes of header length of data part start and end; i recommend start looking into this wiki page and try to read values using fread http://en.wikipedia.org/wiki/Portable_Network_Graphics
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For my project I'm experimenting with disguising the content of a file and thought a good way to do this would be to change the document signature (magic numbers). I think in order to do this I need to change the starting x bytes of the hex but am not sure if this is possible? I've tried looking at the file I want to change in various hex viewers such as autopsy but it strips back all the metadata and only shows the content of that file and the corresponding hex. My question is it possible to change the signature and if so what is the best way to go about it? Any program recommendations?
How to convert image.png or image.bmp to integer array? (do not use any non-standard library)
Please ignore chunks that are not directly related to image data.(IHDR、IEND...etc.)
thank you very much.
SOLVED: I should use binary I/O function in stdio.h to read image file. thanks
If you have to read images into arrays without any image processing libraries you need two things:
You need means to read files in general.
You need to know the internal structure of the file formats you want to read.
So for png refer to https://www.w3.org/TR/2003/REC-PNG-20031110/
This document will tell you where to find the image dimensions, pixel data and other features. It's basically a manual for software developers on how to use this standard format properly.
Some image formats will require additional work like decrompression.
I have a array containing data. This array contains only image data/ or it can be just random data. No header information is available. So writing this to a file and making its extension as jpg is not going to work. Can someone please recommend a library that would do this for me.
Any language that isnt a scripting language is ok. Any environment. I would prefer if its in C/Java/Matlab.
If you have your array in MATLAB (let's say it's in a variable called im), then you can just type
imwrite(im, 'myfilename.bmp', 'bmp')
and your array will be written to a .bmp file. You can choose from a number of other common formats too. See the documentation for imwrite.
You can even write random data in this way:
a = rand(100,100);
imwrite(a,'testimg.jpg','.jpg')
In ruby how to check a string is an actural string or a blob data such as image, from the data type of view they are ruby string, but really their contents are very different since one is literal string, the other is blob data such as image.
Could anyone provide some clue for me? Thank you in advance.
Bytes are bytes. There is no way to declare that something isn't file data. It'd be fairly easy to construct a valid file in many formats consisting only of printable ASCII. Especially when dealing with Unicode, you're in very murky territory. If possible, I'd suggest modifying the method so that it takes two parameters... use one for passing text and the other for binary data.
One thing you might do is look at the length of the string. Most image formats are at least 500-600 bytes even for a tiny image, and while this is by no means an accurate test, if you get passed, say, a 20k string, it's probably an image. If it were text, it would be quite a bit (Like a quarter of a typical novel, or thereabouts)
Files like images or sound files have defined blocks that can be "sniffed". Wotsit.org has a lot of info about the key bytes and ways to determine what the files are. By looking at those byte offsets in your data you could figure it out.
Another way way is to use some "magic", which is code to sniff key-bytes or byte-types in a file to try to figure out what its type is. *nix systems have it built in via the file command. Do a man file or man magic for more info or check Wikipedia's article on Magic numbers in files.
Ruby Filemagic uses the same technique but is based on GNU's libmagic.
What would constitute a string? Are you expecting simple ASCII? UTF-8? Or text encoded some other way?
If you know you're going to get ASCII text or a blob then you can just spin through the first n bytes and see if anything has the eight bit set, that would tell you that you have binary. OTOH, not finding anything wouldn't guarantee that you had text.
If you're going to get UTF-8 Unicode then you'd do the same thing but look for invalid UTF-8 sequences. Of course, the same caveats apply.
You could scan the first n bytes for anything between 0x00 and 0x20. If you find any bytes that low then you probably have a binary blob of some sort. But maybe not.
As Tyler Eaves said: bytes are bytes. You're starting with a bunch of bytes and trying to find an interpretation of them that makes sense.
Your best bet is to make the caller supply the expected interpretation or take Greg's advice and use a magic number library.
Is there a good way to see what format an image is, without having to read the entire file into memory?
Obviously this would vary from format to format (I'm particularly interested in TIFF files) but what sort of procedure would be useful to determine what kind of image format a file is without having to read through the entire file?
BONUS: What if the image is a Base64-encoded string? Any reliable way to infer it before decoding it?
Most image file formats have unique bytes at the start. The unix file command looks at the start of the file to see what type of data it contains. See the Wikipedia article on Magic numbers in files and magicdb.org.
Sure there is. Like the others have mentioned, most images start with some sort of 'Magic', which will always translate to some sort of Base64 data. The following are a couple examples:
A Bitmap will start with Qk3
A Jpeg will start with /9j/
A GIF will start with R0l (That's a zero as the second char).
And so on. It's not hard to take the different image types and figure out what they encode to. Just be careful, as some have more than one piece of magic, so you need to account for them in your B64 'translation code'.
Either file on the *nix command-line or reading the initial bytes of the file. Most files come with a unique header in the first few bytes. For example, TIFF's header looks something like this: 0x00000000: 4949 2a00 0800 0000
For more information on the TIFF file format specifically if you'd like to know what those bytes stand for, go here.
TIFFs will begin with either II or MM (Intel byte ordering or Motorolla).
The TIFF 6 specification can be downloaded here and isn't too hard to follow