I'm working with C# and a usb webcam that supports YUY2 or MJPG image formats. Thus far I've always had it in YUY2 mode and that works fine. Recently I tried changing the format to MJPG thinking that it would then feed my program one JPEG image per frame capture. It appears to almost do that. When I try to display the buffer, my app always takes an exception which is vague, but seems to indicate that the stream is invalid. I then copied one of the buffers to a file and tried to view it with IrfanView and it tells me that there is no huffman table. Looking at the buffer with a binary editor, I see it does have the SOI and EOF JPEG markers (and several others); however, it doesn't contain a huffman table marker. Any ideas what I'm doing wrong here? I've read a bit about JPEG and apparently there are cases where images can use a standard huffman table to reduce file size; however, if that's the case, how do I insert this into the image (if appropriate)?
This is with reference to Microsoft Lifecam by the way.
Part of the Motion-JPEG standard for AVI files is that a fixed Huffman table will be used so that it doesn't have to be stored in every frame.
Related
I want to be able to set the "Title" and "Comments" (listed in properties->details) of some mp3 files in Windows using python. Is this possible, perhaps with a library like PyWin32? Also, would these details be visible in other operating systems or are they Windows-specific? Thanks.
Simple Answer:
Yes, you can set 'Title' and 'Comments' (and many other fields) of an mp3 file in Windows using Python.
Also, the details are visible on all operating systems and are not windows specific.
First you have to understand what is mp3 file and how data is organized within an mp3 file.
Detailed Answer:
Raw audio consumes a lot of size. For example, an audio signal of 10 sec sampled 48 kHz and having a bit depth of 16 bits per sample will be of size 10*48000*16 bits, which is close to 1 MB. So, for a 5 minute song, it will almost take 30 MB. But, if you observe, most 5 min mp3 songs are of size around 5 MB (of course it depends on sampling frequency, bit depth and amount of compression used). How is it possible? It is possible because we compress the data using signal processing techniques which in itself is a big topic altogether which we will not discuss here. So, to create an mp3 file we need something called encoder which converts the raw audio data to compressed data and every time you play an mp3 song, decoder is used which converts the data from compressed format to raw audio, which is what you can only listen. So, compression is done for saving storage and also transmission bandwidth (basically saving amount of data to be transmitted over internet).
Now, coming to how data is organized inside an mp3 file. mp3 file will obviously contain the compressed data. In addition many mp3 files contain some meta data (like Title and Comments you mentioned in your question). There are several formats for storing this meta data. So, a decoder which is decoding mp3 file should also support decoding of meta-data, then only you can see the information, other wise you can't see. The meta data is operating system independent, and can be seen on any operating system provided you have a proper decoder.
Finally, yes you can edit the meta data on windows (for that matter on any OS) using python. If you want to do this, using only python without any library, you need to understand how data is organized inside an mp3 file, find the meta-data inside it, edit it and store it back. But, there are libraries and packages in python which support editing meta-data of mp3 file. You can use them directly. Also, the meta data is independent of OS, and once you edit your properties, you should be able to see the properties in any OS provided the decoder you use has the support.
Some links which will help you:
mp3 tag tool
Another stack overflow question which gives details about libraries that support viewing and editing of meta data using Python
I have cached preview files from Capture One (a photo processing program, similar to Lightroom) where I have lost the originals. Capture One saves previews in their proprietary .cop format and I'm not sure how to go about identifying what's what in there.
There are the strings ETIFFTagInteropIFD and JPEG Embedded TIFF Tags seen in the HEX view which suggests that they are somehow embedding a TIFF in there.
I do have original JPEG files with their corresponding COP-file, but when comparing them there isn't much that's similar - which makes sense I guess, since the preview COP-file is roughly half the size of the original.
What conclusions can I draw from this and what are some good tools for going further?
Anyone knows why the image, shown below, is partially gray while loading? I assume it has something to do with progressive JPG, but I haven't seen the grayscale effect before. Is there some kind of a JPG export setting that enables that? How is it called? Can I disable it?
Direct image link
Edit:
The problem could either be the problem described in #KonradDzwinel answer OR my answer, both could look identical:
What is the problem
For some reason the file is saved or produced in way that make the file we call it Lossless JPEG.
I am not sure which software, tool or how this problem is was produced, but that won’t change the fact that your file had have some issues or even corrupted.
How to find the problem in the file
Your file was saved in way that it works identical but it had issues. To check whether your file is healthy or not, it requires a tool to scan/analysis the image file. I use a very nice and easy to use tool (software) called JPEGsnoop (link for download). This tool is free and I used it to scan and analysis your image files for problems.
Your file comes up with few places with following note, (the screen-shot btw shows only one note, but there were more):
NOTE: Scan parsing doesn’t support this SOF mode.
After I have re-saved the file correctly and analysis it again, it does not show any problems or notes:
What I did to create a problem FREE image file
For testing I have used Photoshop 5.5 to open the Lossless file and save it with new name with default jpeg (since I don't have the original file). But correctly I assume you have the original file, and I assume you have Photoshop any version does not matter OR any other image tool. Try to optimize your jpeg file best possible, analysis it and remember/note the saving setting for future wise image saving.
Here is an example of my Photoshop save settings, which result in problem FREE file:
How can I learn more about Lossless JPEG
I won’t go in details of this problem but I will leave some link that explain it in details, I hope also you find this is useful to solve your issue:
http://www.impulseadventure.com/photo/fix-corrupt-jpeg-photo.html
http://fileformats.archiveteam.org/wiki/JPEG
http://fileformats.archiveteam.org/wiki/Lossless_JPEG_%28original%29
http://www.howtogeek.com/142174/what-lossless-file-formats-are-why-you-shouldnt-convert-lossy-to-lossless/
Software JPEGsnoop
http://www.impulseadventure.com/photo/jpeg-snoop.html
Progressively encoded JPEGs contain ten scan layers by default. That means ten iterative layers of image information build on each other to deliver the final visual quality of the image. The first visible scan layer of a progressive JPEG is always highly pixelated and often black & white because it saves on color channel information.
Source (emphasis mine)
Another resource that explores this issue in lengh: http://cloudinary.com/blog/progressive_jpegs_and_green_martians
I am developing a game in j2me. How to handle images in .dat format.
I downloaded some games and extracted jar , found some dat format images and not able to open that images and images size also very less.. what tools I need to use?
Ref link
enter link description here
Not able to find solution?
A dat file could be anything. Depends what the developer felt like doing.
Some developers chose to strip PNG files of their header, and added the header back in the code. This was partly done in order to save a few bytes (because they mattered back then), and partly because of the challenge in doing it like that, and partly because it ensured all images used the exact same palette.
So that's one possibility, but it really could be anything.
As stated by mr_lou, there really isn't anything special about a .dat extension.
The steps to re-compile a file usually start with opening the file up in a hex editor and then looking at the first bits of information in the file. You then basically work from there to re-compile the data necessary for a 'normal' program to interpret the file. In particular, the first 8-16 bytes are often very helpful for determining what type of file it is "supposed" to be.
If you are looking at a png file (that's what I usually prefer to use for art assets) then you can reference http://en.wikipedia.org/wiki/Portable_Network_Graphics to see how a 'normal' png might look. When you're tweaking to save bytes you often strip unnecessary fields from png headers (things like the ancillary chunks) and using a common palette.
However, remember that it's not necessarily image data. It could be things like level data, sound, default stats or any particular amount of stuff.
In follow up to my previous question, I am able to save the backbuffer of a Direct3DDevice to a surface.
I already found the D3DXSaveSurfaceToFile in the DirectX SDK and it works fine! However, I want to record the obtained surfaces to an AVI file.
I also found the AVIFile reference but they are obviously not straight up compatible with DirectX surfaces.
What would be the best way of approaching this problem? I've seen a number of GDI+/MVC based solutions of grabbing HDCs but those are out of the question. I'm also not sure what kind of data AVIFile expects and how to extract it from the D3DSurface.
Please advise! :)
edit:
Post-processing is also an option. I can capture the surface data in a number of formats, specified here, into memory with D3DXSaveSurfaceToFileInMemory. Afterwards, I could compress this data and then store to disk.
How should I be compressing my data? How should I be storing it? Do I store a timestamp along with it? After recording, how should I turn the generated data into an AVI file?
The source code at this link will show you how to do it:
http://gpalem.web.officelive.com/SimulationRecording.html
Edit: Well you don't have to do things exactly like that linked code. You have a D3DSurface so you can just lock it grab the bits and pass them into CAviFile::AppendFrameUsual ... If you want to change its format then use D3DXLoadSurfaceFromSurface. I didn't say the link was a perfect solution but it DOES show you how to write the frames into an AVi file.
Edit2: As I didn't answer your edit I should do. Firstly don't bother with compression until you have got uncompressed working. Compression is a significantly more complicated thing to get right and you won't be able to get proper compression by simply using the various D3DXSurface copying functions. They don't support the kinds of compression you are after. D3DX is for 3D rendering and NOT for video compression.
For video compression you are best off using DirectShow as you can, simply, add any compressors you wish. This will however mean you'll need to write a "source filter" that you can build your graph off. DirectShow is not an easy thing to use but its very powerful. As far as writing the "source filter" goes you can check out the "Push Source" example in the windows SDK. You will need to adapt it to take the data you are retrieving however.
As an aside, going further on my original edit you could use that code as is by intercepting more D3D9 calls. If you hook the SetRenderTarget calls then you can insert whatever render target you like in there and use the, previously, linked code directly ...