Is there a way to obtain (on the client side) the creation/last modification date of an image uploaded via FineUploader? Looking for a solution for JPEGs (where EXIF is available) and PNGs(where EXIF is not available).
It is not possible to determine these values for non- jpegs. For jpegs, you can use a client side EXIF parser, like, https://github.com/jseidelin/exif-js to extract this data.
Related
I have a PDF file which is made of photographs of a book connected in a single PDF file. I'm trying to convert it back to single images in PNG format, every tool I tried asks me to set DPI which alters the size of resulting images, is there a way to get images of the exact same pixel size the original images were?
Most PDFs of books contain a single image per page and depending on the scanner these images can basically be in three different formats: JPEG, JPEG2000 or TIFF. JPEG2000 is rarely used, so your PDF probably contains JPEG and/or TIFF images.
The good thing about JPEG (and JPEG2000) images is that they can be embedded as-is into a PDF! So you can extract the images as they are stored in the PDF. With TIFF this is also sometimes possible (but I don't think always...).
As mentioned by Tim Roberts you should try using pdfimages or hexapdf images to view and extract the images stored in the PDF. This will give you the best result.
Basically I have a document with lots of small images and I need a fast way to build a list of unique images (and identify them in the document), I was thinking of using Base64 conversion to store each unique image in an xml file (or simply store the MD5 hash of each image).
If the images were saved as files somewhere (i.e outside of the document) I'd be able to do this but (unless there's good reason not to) I'd like to learn how to read the image directly from the document.
Specifically, if I have myDoc.InlineShapes(myImageIndex) how can I most efficiently PREPARE that to either convert to Base64 or create a hash?
All the examples I can find assume the image is loaded from file, I'm hoping to load the image directly from the document... (e.g. Convert image (jpg) to base64 in Excel VBA?)
Many thanks in advance,
I want to upload image data to a php script on the server. I have a URL for an image source (PNG, the image might be located on a different server). I load this into a Javascript image, draw this into a canvas and use the canvas.toBlob() method (or a polyfill as it is not mainly supported yet) to generate a blob holding the image data. This works fine, but I recognized that the resulting blob size is much bigger than the original image data.
In contrast if I use a HTML File input and let the user select an image on the client the resulting blob has equal size to the original image. Can I get image data from a canvas that is equal to the original image size?
I guess the reason is that I loose the PNG (or any image compression) when using the canvas.toBlob() polyfill:
value: function (callback, type, quality) {
var binStr = atob(this.toDataURL(type, quality).split(',')[1]),
len = binStr.length,
arr = new Uint8Array(len);
for (var i=0; i<len; i++ ) {
arr[i] = binStr.charCodeAt(i);
}
callback(new Blob([arr], {type: type || 'image/png'}));
}
I am confused by so many conversion steps via image, canvas, blob - so maybe there is an alternative to get the image data from a given URL and finally append it to FormData to send it to the server?
The method toDataURL when using the png format only uses a limited set of the possible formats available for PNG files. It is the 8bit per channel RGBA (32 bits) compressed format. There are no options to use any of the other formats available so you are forced to include redundant data when you save as a PNG. PNG also has a 24bit and 8 bit format. PNG also has several compression options available though I am unsure which is used but each browser.
In most cases it is best to send the original image. If you need to modify the image and do not use the alpha channel (no transparency) but still want the quality to be high send it as a jpeg with quality set to 1 (max).
You may also consider the use of a custom encoder for PNG that gives you access to more of the PNG encoding options, or even try one of the many other formats available, or make up your own format, though you will be hard pushed to improve on jpeg and webp.
You could also consider compressing the data on the server when you store it, even jpeg and webp have a little room for more compression. For transport you should not worry as most data these days is compressed as it leaves the page and most definitely compressed by the time it leaves the clients ISP
I'm working on a photo viewer. In this context, I wrote a small class to be able to read and use some EXIF data, as e.g. image orientation. This class works well for reading.
However, I would add a new option to rotate photos. I want to rotate and write the photo data itself, not just rewrite the orientation tag. I already wrote the code to rotate and save the primary JPEG image, and it works well. But I also need to rotate the thumbnail contained in the EXIF data, if any, to keep the image coherent. For this reason I need to write in the EXIF data, to replace the existing thumbnail.
But this raises some questions, that I've some trouble answering, namely:
Can the EXIF data contains more than 1 thumbnail, and if yes, what is the maximum thumbnail count that an image can contain?
What are the supported formats for thumbnails? (I found JPEG and TIFF, are there other?)
Is there any guarantee in the EXIF standards that the thumbnails are always written in the late EXIF data, just before the primary image?
If not, then each tags containing an offset that points to a location beyond the thumbnail to replace should be updated. So, is there a standard way to iterate through all tags and sub-directories, to recognize which EXIF tags contain offsets, and to update them if needed? Or the only way is to read a maximum of tags and rewrite only that are known?
Or is there a way to guarantee that the size of the newly rotated thumbnail will be smaller or equal to previous thumbnail size to replace with?
Regards
Here are some answers for your questions:
1) The EXIF data is laid out like a TIFF file with 2 pages. The first page is the camera information and the second page is the thumbnail. If you add more pages (with thumbnails), 99.99% of the applications probably won't notice since you'll be doing it differently than the "standard" way. As far as "maximum count", you have 64k of data that can be stored in any JFIF tag. You can put what you want in that 64k.
2) There is only 1 supported EXIF thumbnail format: TIFF. Inside the TIFF there can be compressed (JPEG) or uncompressed data. Again, you're welcome to stick LZW-compressed data in there, but most apps probably won't be prepared to display it properly.
3) The JFIF container format allows for tags with metadata to appear before the main image. The APPx tags contain metadata that can follow the standard or not. You're welcome to stick multiple EXIF APP1 tags into your files, but again, most apps won't be able to properly handle that situation. So the simple answer is that the EXIF data (including thumbnail) must come before the main image and if you put more than 1 thumbnail it will most likely be ignored.
4) If you are modifying a JFIF (including the metadata), you must rewrite the metadata. It's actually quite simple because each tag is independent and has a simple length value instead of relative offsets.
5) You can do anything you want with the size/orientation of your thumbnail as long as you make the EXIF APP1 tag data total size fit within 64k.
Here's what you need to do...
1) Read the source image (and thumbnail if present).
2) Prepare your rotated image (and thumbnail).
3) Write the new metadata with the new thumbnail image.
4) Write the new main image.
If you want to preserve the original metadata along with your new thumbnail, it's pretty easy. Just read the original tags and hold on to them, then write them in the new image. Each JFIF tag is just a 2 byte identifier (FFxx) followed by a 2 byte length and then the data. They can be packed in almost any order and there's no hard limit on how many total tags can appear before the main image.
I have some raw data in a file that I would like to store in an image file (bmp, jpg, png, or even gif (eegad)). I would like this to be a two way process: I need to be able to reliably convert the image file back later and get a file that is identical to the original file.
I am not looking for a how-to on steganography; the image file will probably be one pixel wide and millions of pixels high and look like garbage. That is fine.
I looked into the Imagemagick utility convert, but am intimidated by the large number of options and terse man page. I am guessing I could just use this to convert from a 'raw' black channel to png, but would have to specify a bunch of other stuff. Any hints? I would prefer to work within Imagemagick or using Linux utilities.
If you are wondering, there's nothing black hat or cloak and dagger about my request. I simply want to automatically backup some important data to a photo-sharing site.
I'd plow into ImageMagick if that's what you'd prefer anyway.
Specific image formats support storing text data to different degrees, and ImageMagick supports all of the formats you mentioned. I'd choose the one that lets you store what you need.