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452

The "white" pixels in the apple picture contain the picture of a pear, stored at a much higher intensity, i.e. very bright. The "black" pixels in the pear picture contain the picture of an apple, stored at a fairly normal intensity, but scaled down to near black with the gamma correction. The image contains a gAMA chunk specifying a file gamma value of ...


188

This was a little too much for a comment, but hopefully it helps. So, I am fairly certain that this issue deals with the way the browsers interpret gamma information with PNGs. It's a pretty fun problem and deals with the ambiguities of gamma information in the first place. The article The Sad Story of PNG Gamma “Correction” provides a very nice summary of ...


186

PNG is compressed, but lossless The compression level is a tradeoff between file size and encoding/decoding speed. To overly generalize, even non-image formats, such as FLAC, have similar concepts. Different compression levels, same decoded output Although the file sizes are different, due to the different compression levels, the actual decoded output ...


157

PNG is lossless. GIMP is most likely just not using the best word in this case. Think of it as "quality of compression", or in other words, "level of compression". With lower compression, you get a bigger file, but it takes less time to produce, whereas with higher compression, you get a smaller file that takes longer to produce. Typically you get ...


87

Your best bet would be to use Imagemagick I am not an expert in the actual usage, but I know you can pretty much do anything image related with this! An example is: convert image.png image.jpg and it will keep the original as well as creating the converted image. As for batch. I think you need to use the Mogrify tool (from the same command line when in ...


60

In xkcd style from lbrandy.com:


49

Or without installing anything: qlmanage -t -s 1000 -o . picture.svg It will produce picture.svg.png that is 1000 pixels wide. I have tested it only on OS X 10.6.3.


48

If you have imagemagick installed, you can just type: convert myfile.pdf myfile.png Though personally I prefer the results obtained from pdftoppm from Poppler utilities: pdftoppm -png myfile.pdf > myfile.png


38

This is overkill for what you need, but in the absence of another answer, GIMP can do this for you. Just install it, open the PDF, and save-as a PNG.


38

From What is the difference between TIFF, GIF, JPG, JPEG, PNG, and a BMP file? BMP - Bitmap. This was probably the first type of digital image format that I can remember. Every picture on a computer seemed those days to be a BMP. In Windows XP the Paint program saves its images automatically in BMP. However, in Windows Vista and later images are now saved ...


38

rsvg-convert did the trick for the SVG I wanted to convert: $ sudo apt-get install librsvg2-bin $ rsvg-convert -f pdf -o t.pdf t.svg rsvg-convert -f pdf doesn't rasterize the SVG, and it embeds and subsets fonts (at least it has embedded the used characters of the Arial font). Sometimes font embedding fails (e.g. for the LMRoman17 font), and the whole ...


36

You should be aware of a few key factors... First, there are two types of compression: Lossless and Lossy. Lossless means that the image is made smaller, but at no detriment to the quality. Lossy means the image is made (even) smaller, but at a detriment to the quality. If you saved an image in a Lossy format over and over, the image quality would get ...


29

There are several ways to get an "uncompressed" AVI out of ffmpeg, but I suspect you actually mean "lossless." Both terms have a fair bit of wiggle room in their definitions, as you will see. I'm going to anchor this discussion with the 720p HD version of Big Buck Bunny, since it's a freely-available video we can all test with and get results we can ...


29

Changing the gamma of an image consists in modifying the value gamma in: (R',G',B') = (Rɣ, Gɣ, Bɣ) which gives the output pixel color (R',G',B') displayed on the screen after applying the gamma function to the initial pixel values (R,G,B) (considering R,G, and B normalized between 0 and 1). Now, let's take the red channel for example. If R ...


26

Excel lacks any user-accessible support for this functionality, but you can either easily work around this or dig in to VBA, where this functionality is provided: "One-shot" export Select the graph (the whole graph, not an internal component; so select the border). Copy it (ctrl-c, right-click copy, whatever you like). Open MS Paint. Paste (you may wish ...


26

All image formats (even vector) must maintain a rectangular border specifying the size of the image. However, one can use the transparent properties of PNG images to simulate the appearance of a non-square image. Just create your image/shape, ensure the background is transparent, and save the file in the PNG format. Make sure you include the alpha ...


24

The existing answers include very little technical data, so I'll include that here. JPEG: up to 24-bit color (possibly more?), variable (usually high) compression, lossy, no alpha support PNG: up to 48-bit color, moderate compression, lossless, alpha support BMP: up to 24-bit color, very little compression, lossless, alpha support GIF: up to 8-bit color, ...


22

Use GIF if the image has few colors (like icons). Can also be used for animated images (like ad banners). Use JPG if the image has many colors (like photos). JPEG is the same thing. Use BMP if you want to save the image without compression. Much larger filesize! Use PNG if you want to publish the image on the web and be up-to-date on modern standards. Pros: ...


22

PNG compression happens in two stages. Pre-compression re-arranges the image data so that it will be more compressible by a general purpose compression algorithm. The actual compression is done by DEFLATE, which searches for, and eliminates duplicate byte-sequences by replacing them with short tokens. Since step 2 is a very time/resource intensive task, ...


21

No need for any additional tools. OS X has sips, which can convert images to (almost) any format. For example, to convert every .gif to .jpeg, putting them into a folder called jpegs: mkdir jpegs sips -s format jpeg ./*.gif --out jpegs Or, to recursively convert them using find, which will place a JPEG file with the same name as the GIF next to it. find ...


21

Make your selection Edit -> Copy Merged File -> New (Photoshop should automatically suggest a new canvas size to match the selection size) Edit -> Paste File -> Save As (PNG) Rinse and repeat... (keyboard shortcuts are handy here) (Tested on Photoshop CS4)


19

Here is one thing you can do. Copy the image you want to multiply. (CtrlA and CtrlC) Make a new 'Black' color layer and click 'add mask'. alt-click the Mask icon, so that you can enter to mask edit mode. Paste your 'multiply' images in the mask (b/w) , and then invert it. You will have a black layer with your multiply material masked. You can adjust ...


18

For most file formats, yes. For example, PNG files are composed of typed chunks, so you could add a chunk named aAAA or lOLZ with arbitrary data. JPEG has "application-specific" segments APPn; the Exif tags in JPEGs are actually a complete TIFF structure inside such a tag. Other formats such as GIF are not extensible, but they often do have a field for ...


18

Using ImageMagick: identify -verbose image.png ImageMagick should be cross-platform. I tried it on Linux with your attached image: [...] Properties: Author: Hans Müller Date: 2010-12-08 09:45 date:create: 2010-12-08T13:15:43+01:00 date:modify: 2010-12-08T13:15:43+01:00 Desc: A long time ago in a galaxy far far away.... signature: ...


17

PngOptimizer 165KB in about 2 seconds. Image quality is untouched.


17

The convert command found on many Linux distributions is installed as part of the ImageMagick suite. Here's the bash code to run convert on all PNG files in a directory and avoid that double extension problem: for img in *.png; do filename=${img%.*} convert "$filename.png" "$filename.jpg" done


17

ImageMagick is an extremely versatile command-line image editor, which would probably rival Photoshop if it had, you know, a GUI. But who needs those anyways. :P Something like the following would convert a .svg to .png, after installation: $ convert picture.svg picture.png The original .svg isn't deleted.


15

I have a couple more solutions. The simplest solution is like most already posted. A simple bash for loop. for i in *.png ; do convert "$i" "${i%.*}.jpg" ; done For some reason I tend to avoid loops in bash so here is a more unixy xargs approach, using bash for the name-mangling. ls -1 *.png | xargs -n 1 bash -c 'convert "$0" "${0%.*}.jpg"' The one I ...


15

As far as I know, these are the only reasons: AnimGIF. This animation works everywhere. There's APNG format, but it's not as widely supported, and has no real editing tools. 1x1 transparent graphic, assuming you care whether it's 80b or 120b. That's virtually the only case in which GIF gives smaller file size than PNG. If you don't have proper tools for ...


15

This works on Ubuntu Lucid: $ sudo apt-get install inkscape $ inkscape t.svg --export-pdf=t.pdf The command-line Inkscape invocation above works even in headless mode, without a GUI (DISPLAY=). However, installing Inscape installs lots of dependencies, including X11. Please note that the exit status of Inskscape is always 0, even if an error occurs -- so ...



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