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What are the different usecases of PNG vs. GIF vs. JPEG vs. SVG? [closed]
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Closed 9 years ago.
I'm using ImageMagick to convert some files from one format to another. I was always under the impression that .png files were supposed to be as big/small as .jpg if not smaller, and definitely smaller than .gif.
However when I run
convert photo.jpg photo.png
The files I'm getting out is about 6 times bigger than the original jpg.
Original jpg is a regular photo about 300x500 px, 52 kb. Output is a proper png of the same dimensions, but size is about 307 kb?
Does anyoone know what the hack is going on? Am I doing something wrong?
P.S.:
I tried both on Debian and Windows with the same results.
P.P.S.:
Also when I add resize option to this and resize to 10000 x 10000. Converting and resizing to jpg takes a few seconds, but it works, if I do the same of png, I jsut strt running out of memory altogether
P.P.P.S.:
For people who keep marking this question as duplicate of PNG vs. GIF vs. JPEG vs. SVG - When best to use? . Please read carefully and understand the question. It's not a duplicate, since this question asks' about files produced programmatically with specific application (image magick). The question you marking as duplicate, is asking which image format is better to use on the web. Two DIFFERENT questions.
The key thing to note here is that each image file format is best for specific purposes.
JPEG stands for “Joint Photographic Experts Group.” That right there should tell you that the .JPG file format is optimized for photographs. It doesn’t work so well for line-art, logos, gradient or tiled / patterned backgrounds, and the like. .JPG’s DCT (Discreet Cosine Transform) artifacts (the “blocky” artifacts we all know and loathe) are much more noticeable with line art and logos than with photos.
PNG has replaced GIF for everything that GIF was ever good for, except one, and that only because no clear standard has emerged: animations. Animated .GIFs are well known on the Web. There are two competing standards for animated .PNGs: APNG and MNG.
APNG is supported in most modern browsers, and is also fully backwards compatible (the file extension is .PNG, not .APNG, and if any program that can display .PNGs but doesn’t know APNG is “fed” an APNG, it will display either a stand-in image of the developer’s choice, or the first frame of the animation if no such stand-in was provided — as far as the older program is concerned, it’s just an ordinary single-frame .PNG with that one image in it — the rest is safely ignored). Gecko (FF, etc.) and Presto (Opera) support it natively, and Google Chrome (using Webkit) can with an add-on.
MNG has the backing of the actual PNG-format development team, but is its own format and is not backwards compatible, but is more powerful and flexible. Right now, only KHTML-based browsers (Konquerer) support it: not Trident (IE), Gecko, Webkit (Chrome, Chromium, Safari), nor Presto.
PNG does everything (except animations unless enhanced with APNG) that GIF does, and better. All else being equal, a .PNG will almost always be smaller than a .GIF at the same resolution and bit depth. Like .GIF, .PNG can support color depths up to 8 bits per pixel in indexed-color (paletted) mode, but unlike .GIF (yet like .JPEG) it also supports direct-color mode at 24 bits per pixel.
In either mode it can add 8 bits of alpha transparency, unlike .GIF (which can only do indexed color transparency [pick a color out of the palette to be replaced with 100% transparency, aka invisibility] — .PNG can do that, too). Alpha transparency produces much better results than indexed transparency, because the pixels can be partially transparent, whereas with indexed transparency (the only kind available in .GIF) your choices are either opaque or invisible. This makes for “halos” around non-rectangular objects when placed against background colors other than the one the .GIF or indexed .PNG was originally “matted” against. It also inhibits being able to do effects such as glows, drop shadows, and, of course, see-through colored objects (without dithering). Alpha transparency can do all of those things with ease, against almost any background (glows would be largely invisible on a white background, and drop shadows would be invisible on black, but you know what I mean).
Yes, you can do 8-bit alpha transparency in an indexed-color .PNG! And guess what? Even Microsoft Internet Explorer 6 can display those just fine, complete with transparency! It’s only the 32-bit .PNGs (24-bit RGB color + 8-bit alpha) that IE6 choked on and displayed as gray!
The most well-known program that can export PNG8 (indexed color) with alpha transparency is Adobe (formerly Macromedia) Fireworks. The Photoshop “Save for Web and Devices” (at least as of CS3) could not do that, despite having basically lifted the feature from Fireworks when Adobe bought out Macromedia. It can save PNG8, but only with indexed-color transparency.
Anyway, full 32-bit (or even 24-bit) PNGs will be pretty large, though usually much smaller than the nearest equivalent .BMP or .TGA or uncompressed .TIFF or some such (unless you’re trying to do a photograph with it — that’s what JPEG is for!). It will usually be somewhat smaller even than .RLE (losslessly compressed .BMP) or losslessly compressed .TIF, all else being equal.
Unlike most of these other formats, PNG also supports 48-bit RGB color, with optional 16 bits of alpha transparency, for extremely high quality (much higher than most monitors can display). These are best used as an intermediate storage format, to retain information from a high bit depth scanner or camera (RAW mode) or some such. Their file sizes would be quite large, despite the lossless compression.
One thing that .PNG cannot currently do is handle non-RGB color spaces such as CMYK or L*a*b.
In short:
For photographs, use .JPG.
For line art and logos of limited color, use indexed-color .PNG (PNG8), with alpha transparency if needed.
For line art and logos of extensive color (e.g. lots of gradient fills, metallic chrome-type reflection effects, etc.), use direct-color .PNG (PNG24) with alpha if needed, if you want the best quality or need transparency (and don’t mind it not working in IE6 or use one of a variety of IE6 workarounds for transparent PNGs), and don’t mind the larger files and bandwidth usage. Otherwise, use .JPG, but be aware that the quality will be degraded. You may need to crank the JPEG quality up pretty high, especially for logos or other graphics with “text” in them, which would reduce your file size savings.
For non-Flash/Silverlight/video/HTML5 Canvas animations, .GIF if the main choice at present, but be prepared to switch to APNG (I don’t think MNG is going to beat it, despite the more official support from the JPEG developers).
JPG is a lossy compression algorithm while PNG is a lossless one.
This fact alone will (in general) make JPG images smaller than PNG ones. You can tweak the compression ratios for each format, so it could also be that you're not compressing your PNG files as much as your JPG ones.
For a photographic image saving as JPG will usually produce a smaller file than PNG as there's more noise or randomness in the image for the compression to work with. Images created by graphic art tools will tend to have more hard edges and areas of solid colour which will compress better in PNG.
If you have text in your image then PNG is going to produce a better quality image as the harder edges of the characters won't be blurred like they would be if JPG is used.
GIF is smaller because it's based on an colour palette (of 256 colours) rather than the separate RGB values for each pixel (or group of pixels) in JPG and PNG.
The PNG format can provide images of 24 bits per pixel or 8 bits per pixel. JPG is a 24 bit format, but it uses lossy compression to reduce the file size significantly. PNG and GIF both use lossless compression, but GIF only works with 8 bits so it requires your image to have 256 colors or less - this often results in a grainier picture.
Try the -colors and -dither options in ImageMagick to reduce the number of bits in your PNG output. At that point it should be comparable to the GIF file size. If you need to reduce it further, there are utilities to optimize the PNG.
The .jpeg file format is a lossy format, it throws information away. Which makes for good compression ratios. The .gif file format is not lossy but loses other information, it only supports 256 colors. The .png file format is not lossy and preserves the color range.
It depends on the kind of image. JPEG's lossy compression works very well on images with lots of color gradients (i.e. photos).
Try it on an image consisting of areas with the same color separated by sharp edges (screenshots are good, unless they show a photo desktop background, and the fancy window borders and task bar of Vista and Windows 7 also tend to mess this up). JPEG is bad at that kind of thing, and you'll probably find PNG to compress better (probably better than GIF too).
Replying to :
Does anyone know what the hack is going on? Am I doing something wrong?
yeah I study this, you aren't doing nothing wrong, you produced 8-bit/color RGB PNG
I solve it with reduce or compress png with pngnq ( http://pngnq.sourceforge.net/ ) that produce 8-bit/color colormap PNG.
pngnq seems to me the most improved project, since is a fork of others like pngquant etc, and is normally in main stream of Linux distros so I just do this:
convert photo.jpg png:- | pngnq -s 1 > photo.png
For the last upvoter (2016): pngnq as been deprecated in favor of pngquant (https://github.com/pornel/pngquant)
Related
I have an iOS app that displays lots of thumbnails on the screen. It's a requirement that the thumbnails have a transparent background.
I store these images as PNG's so that I can get transparency, but all of the images are photographs, so JPEG compression would be perfect for this use case.
In testing, using JPEG's instead of PNG's cuts my disk usage by 90% on average and would reduce needless disk I/O. Unfortunately, I can't make the switch because I would lose the transparency information.
Is there a variant of JPEG (ideally, something that works with the iOS SDK) that allows me to compress photographic images but still keep transparent pixels? I don't actually need a full alpha channel - I just need some pixels to be fully transparent and some to be fully opaque.
I am told that it is possible to use a JPEG with a transparency mask using SVG. I also understand there is 3d party code to display SVG files in IOS.
My app requires that each user has a profile picture of around 140*140px. Right now I am using jpgs, I am wondering if performance wise it will be better to use pngs. I read pngs are good for small UI elements and images, jpg for large images with detail such as photos. Obviously my profile pics are photos but they are small. Would it make much difference switching to png? Thanks
JPEG is best for small file sizes of photos, even for low resolutions.
PNG makes sense when there are many pixels of the exact same color next to each other. This is not the case with photos.
These should be helpful for you.
When to use PNG or JPG in iPhone development?
PNG vs. GIF vs. JPEG vs. SVG - When best to use?
Apple optimizes PNG images that are included in your iPhone app bundle. In fact, the iPhone uses a special encoding in which the color bytes are optimized for the hardware. XCode handles this special encoding for you when you build your project. So, you do see additional benefits to using PNG's on an iPhone other than their size consideration. For this reason it is definitely recommended to use PNG's for any images that appear as part of the interface (in a table view, labels, etc).
As for displaying a full screen image such as a photograph you may still reap benefits with PNG's since they are non-lossy and the visual quality should be better than a JPG not to mention resource usage with decoding the image. You may need to decrease the quality of your JPG's in order to see a real benefit in file size but then you are displaying non-optimal images.
File size is certainly a factor but there are other considerations at play as well when choosing an image format.
I need to edit a png image,by giving it border and drop shadow effect. But the final size of the edited image is too high to use for a mobile app .I know that size of jpeg is less compared to that of png.So i convert that image to jpeg and tried to give drop shadow and border effect.But that image is not having transparent background..Is their any other methods to accomplish this using jpeg?
Another option is to try either ImageOptim for losseless compression, or its lossy cousin, ImageAlpha.
ImageOptim tries a series of lossless algorithms to shrink a PNG and selects the smallest result of the bunch. It has taken 25% to 50%+ of quite a few of our images.
ImageAlpha, on the other hand, is lossy and can further crunch the image, with results more like JPEG but without losing Alpha.
You would also do well to disable PNG compression in Xcode as shown here, with additional details here.
What #minitech wanted to say is not about scaling, it's about file compression. jpg and png files usually have some data that could be removed from the file. There are some compression methods to reduce file size (note that is size in kbs, not in scale measurement). Jpg images can reduce file size by reducing image quality, too.
If you want another file type that accepts transparency, there are the gif format, which gives you a smaller file, but have some drawbacks, like a lack of alpha channel (variable transparency). Check this link for more details: http://www.w3.org/QA/Tips/png-gif
There are a couple of online file compressors. If you want to compress png files, you could try using http://tinypng.org/
No, jpeg image wont support transparency.But you can change the white background coming along with jpeg image
For some reason, when I load a JPG image at design-time, the image shows as a grey scale image with vertical bars reminiscent of TV scan lines. and the image is not sized properly. The image is 500x364 32 bpp, and previews beautifully.
Is there a limitation of TImage in terms of colour depth?
The JPEG implementation in Delphi has some bugs in them.
What do you mean by 32 bit JPEG? If you mean CMYK JPEG files? If so, then you just hit a major problem area in the JPEG implementation in the JPEG unit.
Note hat there are other JPEG packages that you can download as shareware, like NativeJPG, (I don't know if there are freeware packages) that do support CMYK JPEG files correctly.
It was a long time ago... But the answer is Yes for sure, It's just that You have to do the loading of the JPEG separately in Your code.
I don't remember exactly how, but I remember seeing it done easily;)
I'm looking for software to create PNG8 format transparent images as per this article.
NOTE: I need a Linux solution myself, but please submit answers for other OSes.
pngquant does a good job of converting to PNG8 while preserving full transparency.
If you're size-conscious, you may also be interested in pngcrush, which can usually (losslessly) compress PNG files quite a bit.
I also needed a Linux solution and found pngnq to do a pretty good job. It seems to be designed specifically for creating 8-bit PNG images with alpha channels.
apt-get install pngnq # If on Ubuntu/Debian
For Mac: ImageOptim and ImageAlpha are GUIs that run pngcrush, pngquant, and various other normally command-line compression utilities. http://pngmini.com/
The link you provided references ImageMagick, which is an excellent toolkit for manipulating images on Linux.
Ah, if I remember correctly, when I have read this article some months ago, pngquant hadn't a Windows version. I see it has one now. So I tried it, and pngnq too.
The latter seems to do a slightly better job on the IceAlpha.png test image (from libpng.org), at the cost of a slightly bigger image (it can be post-processed with pngcrush or pngout anyway).
The dithering algorithms (the two of pngquant, the only one of pngnq) are different, and it might be worth having both tools, converting images with all algorithms and see what looks the best.
For the record, on the Windows side, IrfanView (4.10) displays these images very well (using the transparency level on each palette entry) while XnView (1.85.1) and GIMP (2.4) apply only a full transparency/opaque display, à la GIF: the light bulb given as an example in the linked article has a transparent background around it, but the orange part is fully opaque.
And the excellent utility TweakPNG shows we have a PLTE (palette, 222 entries) chunk and a tRNS (alpha values for palette colors, 222 entries) chunk. Even more, it allows to edit each palette entry, color and alpha level. It might be an interesting complementary tool for this format.
Note on IrfanView support: if it handles PNG8 correctly for transparency, it doesn't handle gamma information in PNG files: on the toucan image or the ping-pong image, I had to apply a gamma of 2.4 to get similar (lighter) colors.
Note also that IrfanView does an awful job of converting 32-bit PNG images to 256, allowing only one transparent color, which looks bad if full color was dithered!
I see that the GIMP manual states: "his “PNG8” format, like GIF, uses only one bit for transparency; only two transparency levels are possible, transparent or opaque. "
while the ISO/W3C standard states:
"The tRNS chunk specifies either alpha values that are associated with palette entries (for indexed-colour images) or a single transparent colour (for greyscale and truecolour images).". The PNG specification 1.2 added: "Although simple transparency is not as elegant as the full alpha channel, it requires less storage space and is sufficient for many common cases."
It looks like the unique transparent color is more implemented than the full transparency palette, alas. At least browsers get it right.
It depends on what exactly your original images look like.
If your images already contain 256 or fewer colors (RGBA values), you need only look at pngout (Windows) (Linux/BSD/Mac OS X ports), which you should already be using to optimize your PNG images anyway. It can't quantize images, but it can save them as 8-bit, including alpha transparency. Just pass in the /c3 (or -c3 on Linux et al.) color option to force it to save the image as PNG8.
If your images do contain more than 256 colors, you have a few more, but all less than perfect options:
Adobe Fireworks is probably the best option in terms of the resulting image quality. It will do the job if you only need to convert a few images, or if you don't mind relying on Fireworks to do the batch processing. I did find that it sometimes somehow limits the number of colors in the palette, creating a worse quality image than necessary. I don't know if that's perhaps a bug in CS3 that's been fixed in CS4.
If you're not on Windows or OS X this obviously isn't an option, and buying Fireworks just for this probably isn't worth it either.
The only alternatives I know of are the already mentioned pngquant and pngnq. I've had better luck with pngnq, but that's probably just going to depend on which quantization strategy works best on the files you're working with.
Unfortunately, I've noticed that neither of them work very well with small amounts of transparency (say, an opaque image with transparent, rounded corners).
I recommend "The GIMP" as it is possible to output in PNG8 and supports Linux/Windows. If you want a quick Windows-only solution, I also recommend IrfanView.
Microsoft Windows: Ultimate Paint (freeware and shareware
versions are available).
Both versions can save as an 8 bit transparent PNG image.
It can also save as a 4 bit PNG (16 colours). This cuts the
file size in half compared to 8 bit.
Input formats include BMP, GIF, ICO, JPG/JPEG and PNG.
The freeware edition of Ultimate Paint Standard 2.88 LE can
be downloaded directly from
http://www.ultimatepaint.com/up.zip (1.7 MB).