I have images that I upload to a server using Amazon S3. I convert them to NSData, using UIImageJPEGRepresentation with 0.75f compression quality. Now I'd like to compare them and see if they are equal.
With PNG, it's easy, all I had to do is this:
if (UIImagePNGRepresentation(self.pictureImageView.image) isEqual:
UIImagePNGRepresentation(manageItemVC.pictureImage)]) {}
as stated here. And that would work, but now the images are JPEG, and the comparison isn't working (most likely due to compression), even if I use UIImageJPEGRepresentation.
self.pictureImageView.image is the image from the server that I've loaded into an UIImageView, and manageItemVC.pictureImage is an image that the user picked from the photo library.
Anyone know how to compare JPEG images?
You can check data's length of two image and compare it.
With my suggestion, i check if two data different about 10000 => two image different.
Related
Am working on Qccpack for Hyperspectral image compression which uses .icb extension.
How can I convert from ENVI .hdr to .icb in order to work with Qccpack ?
I just had a quick look into the Qccpack documentation. (the first thing I found via google, I guess this is what you are talking about)
http://qccpack.sourceforge.net/Documentation/QccIMGImageCubeFree.3.html
.icb is a file that stores "image cubes". They say that image cubes are a data structure for saving volumetric image data.
ENVI .hdr instead is a file format that stores meta data for an image that is stored in another file.
You cannot convert image meta data into image data.
For a specific purpose I am trying to convert an AVI video to a kind of Moving JPEG format using OpenCV. In order to do so I read images from the source video, convert them to JPEG using imEncode, and write these JPEG images to the target video.
After several hundreds of frames suddenly the size of the resulting JPEG image nearly doubles. Here's a list of sizes:
68045
68145
68139
67885
67521
67461
67537
67420
67578
67573
67577
67635
67700
67751
127800
127899
127508
127302
126990
126904
Anybody got a clue what's going on here?
By the way: I'm using OpenCV.Net as a wrapper for OpenCV.
Thanks a lot in advance,
Paul
I found the solution. If I explicitly enter the third parameter to imEncode (for JPEG encoding this indicates the quality of the encoding, ranging from 0 to 100) instead of using the default (95) the problem disappears. It's likely this is a bug in OpenCV.Net, but it could also be a bug in OpenCV itself.
I am doing image manipulation on the png images. I have the following problem. After saving an image with imwrite() function, the size of the image is increased. For example previously image is 847KB, after saving it becomes 1.20 MB. Here is a code. I just read an image and then save it, but the size is increased. I tried to set compression params but it doesn't help.
Mat image;
image = imread("5.png", -1);
vector<int> compression_params;
compression_params.push_back(CV_IMWRITE_PNG_COMPRESSION);
compression_params.push_back(9);
compression_params.push_back(0);
imwrite("output.png",image,compression_params);
What could be a problem? Any help please.
Thanks.
PNG has several options that influence the compression: deflate compression level (0-9), deflate strategy (HUFFMAN/FILTERED), and the choice (or strategy for dynamically chosing) for the internal prediction error filter (AVERAGE, PAETH...).
It seems OpenCV only lets you change the first one, and it hasn't a good default value for the second. So, it seems you must live with that.
Update: looking into the sources, it seems that compression strategy setting has been added (after complaints), but it isn't documented. I wonder if that source is released. Try to set the option CV_IMWRITE_PNG_STRATEGY with Z_FILTERED and see what happens
See the linked source code for more details about the params.
#Karmar, It's been many years since your last edit.
I had similar confuse to yours in June, 2021. And I found out sth which might benefit others like us.
PNG files seem to have this thing called mode. Here, let's focus only on three modes: RGB, P and L.
To quickly check an image's mode, you can use Python:
from PIL import Image
print(Image.open("5.png").mode)
Basically, when using P and L you are attributing 8 bits/pixel while RGB uses 3*8 bits/pixel.
For more detailed explanation, one can refer to this fine stackoverflow post: What is the difference between images in 'P' and 'L' mode in PIL?
Now, when we use OpenCV to open a PNG file, what we get will be an array of three channels, regardless which mode that
file was saved into. Three channels with data type uint8, that means when we imwrite this array into a file, no matter
how hard you compress it, it will be hard to beat the original file if it was saved in P or L mode.
I guess #Karmar might have already had this question solved. For future readers, check the mode of your own 5.png.
I have a directory structure containing 300 gigs worth of Tiff Images. Some are encoded as Jpeg-in-Tiff, others as "Group 4 fax encoding". I need to change the format of all to the later without losing my folder structures.
Anyone have any ideas?
Pretty much any image viewer with a batch conversion shoudl do this I like irfanview
I'm having a proprietary image format SNG( a proprietary format) which is having a countinous array of Image data along with Image meta information in seperate HDR file.
Now I need to convert this SNG format to a Standard TIFF 6.0 Format. So I studied the TIFF format i.e. about its Header, Image File Directories( IFD's) and Stripped Image Data.
Now I have few concerns about this conversion. Please assist me.
SNG Continous Data vs TIFF Stripped Data: Should I convert SNG Data to TIFF as a continous data in one Strip( data load/edit time problem?) OR make logical StripOffsets of the SNG Image data.
SNG Data Header uses only necessary Meta Information, thus while converting the SNG to TIFF, some information can’t be retrieved such as NewSubFileType, Software Tag etc.
So this raises a concern that after conversion whether any missing directory information such as NewSubFileType, Software Tag etc is necessary and sufficient condition for TIFF File.
Encoding of each pixel component of RGB Sample in SNG data:
Here each SNG Image Data Strip per Pixel component is encoded as:
Out^[i] := round( LineBuffer^[i * 3] * **0.072169** + LineBuffer^[i * 3 + 1] * **0.715160** + LineBuffer^[i * 3+ 2]* **0.212671**);
Only way I deduce from it is that each Pixel is represented with 3 RGB component and some coefficient is multiplied with each component to make the SNG Viewer work RGB color information of SNG Image Data. (Developer who earlier work on this left, now i am following the trace :))
Thus while converting this to TIFF, the decoding the same needs to be done. This raises a concern that the how RBG information in TIFF is produced, or better do we need this information?.
Please assist...
Are you able to load this into a standard windows bitmap handle? If so, there are probably a bunch of free and commercial libraries for saving it as TIFF.
The standard for TIFF is libtiff -- it's a C library. Here's a version for Delphi made by an expert in the TIFF format:
http://www.awaresystems.be/imaging/tiff/delphi.html
There seems to be a lot of choices.
I think the approach of
Loading your format into an in-memory standard bitmap (which you need to do to show it, right?)
Using a pre-existing TIFF encoding library to save as TIFF
Will be a lot easier than trying to do a direct format-to-format conversion. The only reasons I wouldn't do it this way are:
The bitmap is too big to keep in memory
The original format is lossy and I will lose more quality in the re-encoding -- but you'd have to be saving in a standard lossy format (JPEG) to save quality.
Disclaimer: I work for Atalasoft.
We make .NET imaging codecs (including TIFF) -- that are a lot easier to use than LibTiff -- you can call them in Delphi through COM. We can convert standard windows bitmaps to TIFF or PDF (or other formats) with a couple of lines of code.
One approach, if you have a Windows application which handles and can print this format, would be to let it do the work for you, and call it to print the file to one of the many available 'printer drivers' which support direct output to TIFF.