I have seen in picasa that we can find the details of camera and date at which an image is taken. I want to know what kind of other information's can be find out using a digital image. Do you know any tools which can be used for this purpose?
EXIF Tags contain additional information about the image:
Wikipedia "Exchangeable image file format"
It really depends on the image and camera the image was taken with, but the most common fields include: Date, Manufacturer, Model, Orientation, Compression, Flash info, GPS-Info (newer/better cameras) and much more.
There are various tools for reading EXIF data:
- The simplest of all may be the Windows Explorer itself (Right click on the image and you can read all EXIF Tags)
- More sophisticated programs like the Adobe Suite can also be used to read EXIF Data.
Related
I've noticed that many website change all their user-uploaded images to .jpg or .png format.
I am wondering what are the pros and cons of converting images to the same format.
Possible points of consideration are:
Security (I heard it is possible to put malicious code in images of certain filetypes)
Storage
Image quality
Scalability
Typically, after a user uploads a photo to a web application, some processing will be done to the image. For example, if a user uploads an avatar image, it will be cropped so that it is square, and resized so that all avatar images are the same size. Sometimes, we may want multiple resolutions of the same image for different display purposes (avatar icon vs. profile page). ImageMagick is often the tool of choice for performing image processing on the server.
Does parsing of a RAW camera image yield all the necessary informations to create a viewable picture from it?
More specifically, is it possible to obtain informations like sensor layout, crop position and size, ... just from the RAW file?
I'm asking because in the case of crop, there is ActiveArea TIFF tag but it seems it is not always available. Also, I see that RAW conversion software seem to always include a hand-crafted database of attributes like black-point, sensor pattern so I was wondering whether that is some kind of optimisation or that all the required information is simply not there in the RAW?
You know, computer stores images as channels and pixels in those channels. And pixel values are like "00110101" which fills 8 bits at memory. I want to know truly where that bits stored at memory, and how can i make operations on them.
Thanks!
Well, the standard book is Digital Image Processing by Gonzalez and Woods.
Another book, where you can pick up the PDF for free is Image Processing in C by Dwayne Philips - PDF here.
First, you need to get a decent C compiler and development system - personally I use Mac OSX, but I guess you would want Visual Studio free edition on Windows.
Then you need to get started with some simple reading and writing of files and memory allocation. I would go with greyscale images of the NetPBM format - probably just PGM files - described here as they are the easiest. You can download the NetPBM programs and run them in a Windows Command Prompt and see how they work and try and implement them yourself in C. You can also download ImageMagick for Windows and try converting images from colour to greyscale and resizing them like this:
convert input.png -colorspace gray result.jpg
convert input.tif -resize 400x400 result.pgm
When you have got that, I would move on to colour PPM format and then maybe PNG and/or JPEG. Remember there are libraries for TIF/JPEG/PNG/BMP so don't be afraid to use them.
Finally, move on to displaying images yourself with Windows GDI etc.
Come back to StackOverflow if you get stuck - questions are free!
tl;dr wildly different with different encodings/filesystems/os'es/drivers
Well that depends on the image format. BMP is one of the easier formats, details on what these files look like can be found on for instance wiki
And to answer "where its stored", it is stored on permanent storage (hardrive/ssd), where exactly depends on the filesystem (FAT/NTFS/EXT etc).
When an image is to be displayed, its read into memory, where it can be manipulated and through some apis this data can be put into a memory region specifically meant to display the current images on you screen.
I'm building a web application (RoR) that manages images that are in raw image format. I need to create thumbnail/web versions of these images to be displayed on the site. Currently, I'm using imagemagick, which delegates to dcraw to produce the jpeg thumbnail. The problem I'm running into is that the thumbnail deviates from the look of the original; the image gets darker and the white balance is sometimes heavily shifted.
I'm assuming that the raw format default setting can't be read by dcraw, and thus it's left guessing how to parameterize the raw conversion. I can play around with customizing these setting, but it seems getting it right on one image causes others to be further off the mark.
Is there a better way to do this in order to get a result that more closely mimics the what I might see in a raw viewer like photoshop, or even Mac OSX preview? Given that Mac OS X supports a variety of digital camera raw formats, is there anyway to utilize the OS's ability to render preview images (especially considering that result is what is expected).
The raw images that I'm using are 3FRs and fffs (both from Hasselblad).
I can post samples if people are interested.
Thanks
Look at "sips" and "Resizing images using the command line" to get you started.
I'm using an image loader (DevIL) for image loading. Im just wondering if the image format (the uncompressed format in memory) loaded from files (.jpg, .png, .bmp etc) is determined by the image loading program itself, or is some way contingent upon the actual image file.
All of the images I have looked at so far seem to be loaded into the RGBA / UNSIGNED_BYTE format. However I am wondering if I can always rely on this. Is it conceivable that an image might actually be loaded into the RGBA / FLOAT format instead? (NOTE: i am hoping that the loaded image format will always be the same, i want to rely on it:)
I can't find any docs in DevIL that explains this point, so I'm hoping anyone experienced with imaging / image loading could give me an answer just based on their experience / common sense.
Thanks
I don't know DevIL, but nearly any imaging library is going to provide you with an image object that has some concept of Pixel Format. The pixel format tells you how the image is laid out in memory. Looking quickly at the docs, I see that IlTexImage has a property called Format which can be one of IL_COLOUR_INDEX, IL_RGB, IL_RGBA, etc. The docs say
The format of the image data. Formats accepted are listed here and
are self-explanatory