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Posts Tagged ‘format’

PDF (Portable Document Format) documents are a handy way to present text and images to others knowing they’ll look the same no matter what word processor or operating system they use. Basically, they’re a snapshot of a document, so saving images from them can be a hassle, even if your viewer lets you right-click them and save them as files. There are a few programs around that can do this for you, but it’s actually much easier and faster doing this from the command-line.

The pdfimages command is part of poppler-utils, which should already be installed on your system (sudo apt-get install poppler-utils in the terminal if it isn’t). To extract the images from a PDF, just open a terminal in the folder with the document, and run a command like the following:

pdfimages -j Cool-Pix-of-2011.pdf cool2011

Note that when extracting from files with spaces in the name, you will need to enclose the filename in single quotes. Eg:

pdfimages -j 'Cool Pix of 2011.pdf' cool2011

The text at the end of the command is what each extracted image will begin with, so the resulting filenames will be cool2011-000.jpg onwards (note that numbering starts at 000, not 001). Once again, if you’d prefer to have spaces in the target names, for example to mirror the name of the original PDF, then enclose that in single quotes too (eg: 'Cool Pix of 2011 ' – note the space at the end, just to provide a bit more separation between '2011' and the hyphen preceding the automatic numbering; this is of course optional, and you can pretty much do what you want). Eg:

pdfimages -j 'Cool Pix of 2011.pdf' 'Cool Pix of 2011 '

Your pictures will now be extracted into the folder with names starting with Cool Pix of 2011 -000.jpg.

Also, the -j option is to save the images in the .jpg format, otherwise they will be saved in .ppm (Portable Pixmap) format, with each file being over a megabyte. This can mean, for example, that an 18Mb document with 120 images can extract to 154Mb of files, whereas exporting them as .jpg ends up with a total of 18Mb, just like the original document. Of course, if you’d prefer to save them as .ppm images, simply leave out the -j option.

If you would like to include the page numbering in the file names, add the -p option. Eg:

pdfimages -j -p 'Cool Pix of 2011.pdf' 'Cool Pix of 2011 '

Lastly, don’t worry if you see the following in the terminal for each image being extracted:

Error (18468081): Missing ‘endstream’
Error: Unknown operator ‘endstream’
Error: Unknown operator ‘endobj’

You shouldn’t see that with every PDF you try to extract from, but even when you do you should find the target images have been created without issue.

Extra Notes:

For more options for this command, run pdfimages -?. For example, you can specify a start and end page, but personally I find it easier to just extract the whole document and delete any images I don’t want afterwards. But if you need to specify a password, you will find the option here.

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If you’ve attached an external hard drive to your system, then decided to use your partitioner to format it to EXT4 for greater efficiency (or just to match your Ubuntu system), you may have been shocked to find that your empty drive seemed to be missing a few gigabytes when mounted afterwards. And this has nothing to do with the good old binary (base-8) vs decimal (base-10) situation which would see your “750Gb” drive be more like 700Gb (in Windows and earlier versions of Ubuntu – now Mac OS X and Ubuntu have followed hardware manufacturers and use decimal, so that’s more like 738Gb).

This is because Ubuntu (and other Linux distributions) reserve typically around 5% of the space for the root user and system services, so should you run out of hard drive space, the administrator can still log in, and system services continue to run.

However, this is only really needed for your Ubuntu partition, so if you have an external EXT4 drive, or have an EXT4 partition on your internal drive (other than the one your system is on), you are needlessly wasting space (40Gb of the drive in the example). But you can free up that disk space quite easily, without having to re-partition the drive or anything. All it takes is a couple of commands pasted into the terminal.

In the following example, an external hard-drive will have the reserve set to 0 (zero), since this is what most people will need this for. First, we have to determine the device name, as using its mounted name – /media/700Gb Ext4 – won’t suffice. To do so, enter the following into the terminal:

mount|grep ^'/dev'

Look for the line containing your device:

/dev/sdc1 on /media/700Gb Ext4 type ext4 (rw,nosuid,nodev,uhelper=udisks)

… and you can see what it is named (/dev/sdc1 in this case). To free up reserved space, enter the following (replacing /dev/sdc1 with whatever the appropriate device name is, if need be – just make sure you don’t do it to your main drive!):

sudo tune2fs -m 0 /dev/sdc1

You should then be presented with the following message:

Setting reserved blocks percentage to 0% (0 blocks)

To confirm all has gone well, you can right-click an empty area of the folder window for the device and choose Properties, then compare the free space from before and after, or run the following command (once again replacing the device name with the correct one in your case):

sudo tune2fs -l /dev/sdc1 | grep 'Reserved block count'

You should be greeted with the following:

Reserved block count: 0

That’s it – you now have all of your drive to use.

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Note: if you receive the following error message:

tune2fs: Bad magic number in super-block while trying to open /dev/sdb1
Couldn’t find valid filesystem superblock.

… then the filesystem likely isn’t EXT4 – chances are the drive is actually formatted as NTFS or FAT for use on Windows systems (which would be the case if you’ve bought an external drive, and never did anything other than copy files to it). You would have needed to partition/format the drive to EXT4, so if you didn’t, then you actually don’t need this guide.

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If your system is slowly grinding to a halt, and multitasking is a nightmare, you may need to check your swap is in use. If you’re experiencing non-stop, furious hard drive activity resulting from even the most simplest tasks (like clicking another tab in your browser, or even something basic like minimising an app), with things you’ve initiated taking 2 minutes or more to appear, then open a terminal and enter top.

You’ll see “Swap” near the beginning, and if the total is 0k (that’s zero kilobytes), then that means your swap has been deactivated for some reason. To enable it again, start the Partition Editor (found in System > Administration; if it isn’t installed, enter sudo apt-get install gparted in a terminal to do so).

Locate linux-swap, right-click it, and choose Swapon. Your swap partition should now be in use, but if you have further hassles, it might pay to reformat (or even delete) the swap with GParted (ie: Partition Editor). To format it again, just right-click the swap and choose Format > linux-swap.

In case the swap appears on (even if not working), you will need to Swapoff to get the Format options. Similarly, if you decide to delete the swap and start again, you might need to turn it off first so the Delete option is available. The swap can then be recreated with the unallocated space it left when deleted, which you would then format as linux-swap.

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Did this information make your day? Did it rescue you from hours of headache? Then please consider making a donation via PayPal, to buy me a donut, beer, or some fish’n’chips for my time and effort! Many thanks!

Buy Ubuntu Genius a Beer to say Thanks!

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