My experiance with normal archive types for data such as zip/gzip/7zip/lzma/etc.. dont do a good job of image compression
I was wondering if there exists image compression that allow for a very high compression ratio for long term storage, in which the image doesnt need to contain enough data to preview or "look" at the picture, just ensure that the data is reproducable to a normal jpeg/png?
When searching for image compression algorithms, google basically only returns jpeg,png,gif,bitmap. As far as I understand these image types are for compressing images that need to be viewable in their compressed format. But if you didnt need to view it the image when its compressed could you achieve a higher compression ratio.
Thanks
PNG optimized with ZopfliPNG (e.g. via GUI like ImageOptim) will give you pretty good lossless compression.
PNG has prediction filters that help it achieve better compression than bare gzip.
Related
I understand that graphic images do not compress well when using a lossless compression archive file format like .zip. Is there an image file type that losslessly compresses better (smaller) than the others?
Which image file format compresses the most when using a lossless data compression archive file format (like .zip)?
Lossless image compression algorithms implemented in image file format use the same methods as general purpose compression software, plus some specific methods based on image models. These methods tend to remove data redundancy and to provide a variable length coding that exploits data statistics to reduce coding cost.
Hence if a compressed image can be significantly recompressed by, say, zip, it is probably not a very efficient file format in terms of compression. So to answer your question, the image file format that can be the most efficiently compressed by zip is the format with the least internal compression. And the final result will be worse than using a good lossless image compression method and skipping the zip recompression.
There are good lossless image compression methods available. The compression ratio is of course worse than the one provided by lossy compression, but can be decent, depending on your need. In standard methods, you can use png of lossless jpeg2000. And the are very good non standard methods, as webP, FLIF or BPG. But with none of them you will have any significant gain if using zip on these images.
The file format does not affect the compression ratio of the image .it usually tells us what is the data format and the compression used.
The image itself affects the comprrssion. A monothonic image will compress better than a noisy one.
Which lossless compression algorithm [between LZW or JBIG] is better for compressing data sets consisting of images (colored and monochrome) ?
I have implemented both and tested on smaller data sets [each containing 100 images] and have found inconclusive results.
Please Note:: I cannot use Lossy compressions like Jpeg because the data after decompression has to be identical to that of the source. Neither I can other lossless algorithms like PNG as they are not supported by the firmware which is responsible for the decompression.
Neither LZW or JBIG are optimal, although JBIG (JBIG2) should give you better results.
LZW is not designed for images (e.g., it does not exploit 2D correlation), and JBIG. JBIG (perhaps you mean JBIG2?) does exploit the 2D correlation, although it is designed for monochrome images such as fax pages.
Of course, results will depend on your particular dataset, so if results are inconclusive the best thing you can do is to test on more images (and perhaps differenciate between color and grayscale images).
If your firmware supports it, I would also test JPEG-LS (https://jpeg.org/jpegls/), which in my experience gives good overall lossless compression performance.
JPEG-LS or JPEG 2000 would give better results. You can think about WebP or JPEG XR as well.
Note: If you want to render compressed image to browser then you may need to take the browser support into account. e.g. JPEG 2000 supported by safari, WebP supported by chrome and android browsers, JPEG-XR supported by IE11 & Edge likewise.
I am working on an iPad application which has hundreds of photo-quality images. I would have naturally assumed to store these images as JPEGs so as to optimize the app file size. However, Apple's guidelines state:
Use the PNG format for images. The PNG format provides lossless image content, meaning that saving image data to a PNG format and then reading it back results in the exact same pixel values. PNG also has an optimized storage format designed for faster reading of the image data. It is the preferred image format for iOS.
However, if I store the same images as JPEGs at 100% quality, the size of them drops to about half that of the PNG lossless versions.
Is there really that much of a performance hit to use JPEG instead of PNG? If I am viewing these images in a carousel or gallery style, do I really need to worry about the performance and use PNGs instead?
Thanks!
Regarding the quality PNG is good for application kind of images, but JPEG is preferred for photos. Choose the lowest JPEG quality that gives good enough quality for your images.
Regarding speed, size also matters. I have no IPad to test with, but the smaller file size to read from flash or network might very well out weight any additional decompression cost. The only way to find out is to measure on your actual device.
There is a performance consideration but while PNG is preferred for quality, given your application, I'd suggest JPEG would be preferable.
Pure performance isn't the only factor of interest or concern; an iPad has only a finite space available to it, and filling that up with image data that most users are not going to need or want seems preferable to using more computational power for most cases.
One other thing to consider - on a gallery, you are strongly recommended to generate thumbnails which give you the best of both worlds: the smaller, more accessible image for general use and the full original image for 'best'.
If in doubt, benchmark with both and see how big the difference is in your application - and if the difference is something you can live with versus the space saving, go with JPEG.
I'm creating barcodes on the fly, and embedding them in web pages. What format should I use? I'm wavering between JPG and PNG, and I don't really understand the advantages of both. Size matters in this, as does readability (better a clear barcode than a blurry one). Is there another format that would be better yet?
PNG, or even GIF. Jpeg is right out, because it's designed for the smooth gradients of photographs, not the sharp edges of bar codes. Draw a simple Bar code by hand in MS Paint, save it, and then reload it, you'll see all kinds of compression artifacts.
Definitely PNG. It's much better at storing vector graphics, such as bar codes (as opposed to photos).
Wikipedia has a nice comparison of JPG vs. PNG.
PNG should be better than JPG (JPG is lossy). GIF might be even better since the image is going to be monochrome (but check it in your case).
PNG is the better option between PNG and JPG. The main issue here is of compression - there are two forms of compression techniques in images, lossy and lossless. Lossy compression algorithms (such as the one used by JPG files) "lose" information during the compression->decompression cycle. Because of this, there will be artifacts in your image. PNG, on the other hand, uses lossless compression, so the displayed image will be exactly the same as the original, uncompressed imagery prior to the initial saving.
In the case of barcodes, the exact pixel-by-pixel placement of black/white is very important (that's the entire point), so using a lossy compression routine like JPG could be very bad. If you're using a 2D barcode, it will be even worse, and your scanner may have a very difficult time reading the barcode accurately. PNG will completely eliminate this problem.
I have used .gif and .png successfully. My answer (and other answers, to be fair) to this question has more detail.
PNG all the way. It will not only avoid the compression artifacts you'll get with JPG, but will almost certainly yield better compression as well. JPG is very badly suited to images with sharp edges.
I have a very large background image (about 940x940 pixels) and I'm wondering if anyone has tips for compressing a file this large further than Photoshop can handle? The best compression without serious loss of quality from Photoshop is PNG 8 (250 KB); does anyone know of a way to compress an image down further than this (maybe compress a PNG after it's been saved)?
I don't normally deal with optimizing images this large, so I was hoping someone would have some pointers.
It will first depend on what kind of image you are trying to compress. The two basic categories are:
Picture
Illustration
For pictures (such as photographs), a lossy compression format like JPEG will be best, as it will remove details that aren't easily noticed by human visual perception. This will allow very high compression rates for the quality. The downside is that excessive compression will result in very noticeable compression artifacts.
For illustrations that contain large areas of the same color, using a lossless compression format like PNG or GIF will be the best approach. Although not technically correct, you can think of PNG and GIF will compress repetitions the same color very well, similar to run-length encoding (RLE).
Now, as you've mentioned PNG specifically, I'll go into that discussion from my experience of using PNGs.
First, compressing a PNG further is not a viable option, as it's not possible to compress data that has already been compressed. This is true with any data compression; removing the entropy from the source data (basically, repeating patterns which can be represented in more compact ways) leads to the decrease in the amount of space needed to store the information. PNG already employs methods to efficiently compress images in a lossless fashion.
That said, there is at least one possible way to drop the size of a PNG further: by reducing the number of colors stored in the image. By using "indexed colors" (basically embedding a custom palette in the image itself), you may be able to reduce the size of the file. However, if the image has many colors to begin with (such as having color gradients or a photographic image) then you may not be able to reduce the number of colors used in a image without perceptible loss of quality.
Basically it will come down to some trial-and-error to see if the changes to the image will cause any change in image quailty and file size.
The comment by Paul Fisher reminded me that I also probably wouldn't recommend using GIF either. Paul points out that PNG compresses static line art better than GIF for nearly every situation.
I'd also point out that GIF only supports 8-bit images, so if an image has more than 256 colors, you'll have to reduce the colors used.
Also, Kent Fredric's comment about reducing the color depth has, in some situtations, caused a increase in file size. Although this is speculation, it may be possible that dithering is causing the image to become less compressible (as dithering introduces pixels with different color to simulate a certain other color, kind of like mixing pigment of different color paint to end up with another color) by introducing more entropy into the image.
Have a look at http://www.irfanview.com/, is an oldy but a goody.
Have found this is able to do multipass png compression pretty well, and does batch processing way faster than PS.
There is also PNGOUT available here http://advsys.net/ken/utils.htm, which is apparently very good.
Heres a point the other posters may not have noticed that I found out experimentally:
On some installations, the default behaviour is to save a full copy of the images colour profile along with the image.
That is, the device calibration map, usually SRGB or something similar, that tells using agents how to best map the colour to real world-colours instead of device independant ones.
This image profile is however quite large, and can make some of the files you would expect to be very small to be very large, for instance, a 1px by 1px image consuming a massive 25kb. Even a pure BMP format ( uncompressed ) can represent 1 pixel in less.
This profile is generally not needed for the web, so, when saving your photoshop images, make sure to export them without this profile, and you'll notice a marked size improvement.
You can strip this data using another tool such as gimp, but it can be a little time consuming if there are many files.
pngcrush can further compress PNG files without any data loss, it applies different combinations of the encoding and compression options to see which one works best.
If the image is photographic in nature, JPEG will compress it far better than PNG8 for the same loss in quality.
Smush.It claims to go "beyond the limitations of Photoshop". And it's free and web-based.
It depends a lot on the type of image. If it has a lot of solid colors and patterns, then PNG or GIF are probably your best bet. But if it's a photo-realistic image then JPG will be better - and you can crank down the quality of JPG to the point where you get the compression / quality tradeoff you're looking for (Photoshop is very good at showing you a preview of the final image as you adjust the quality).
The "compress a PNG after it's been saved" part looks like a deep misunderstanding to me. You cannot magically compress beyond a certain point without information loss.
First point to consider is whether the resolution has to be this big. Reducing the resolution by 10% in both directions reduces the file size by 19%.
Next, try several different compression algorithms with different grades of compression versus information/quality loss. If the image is sketchy, you might get away with quite rigorous JPEG compression.
I would tile it, Unless you are absolutely sure that you audience has bandwidth.
next is jpeg2k.
To get more out of a JPEG file you can use the 'Modified Quality Setting' of the "Save as Web" dialog.
Create a mask/selection that contains white where you want to keep the most detail, eq around Text. You can use Quick-Mask to draw the mask with a brush. It helps to Feather the selection, this results in a nice white to black transition in the next step.
save this mask/selection as a channel and give the channel a name
Use File->Save as Web
Select JPEG as file format
Next to the Quality box there is a small button with a circle on it. Click that. Select the saved channel in step 2 and play with the quality setting for the white and black part of the channel content.
http://www.jpegmini.com is a new service that creates standard jpgs with an impressively small filesize. I've had good success with it.
For best quality single images, I highly recommend RIOT. You can see the original image, aside from the changed one.
The tool is free and really worth trying out.
JPEG2000 gives compression ratios on photographic quality images that are significantly higher than JPEG (or PNG). Also, JPEG2000 has both "lossy" and "lossless" compression options that can be tuned quite nicely to your individual needs.
I've always had great luck with jpeg. Make sure to configure photoshop to not automatically save thumbnails in jpegs. In my experience I get the greatest bang/buck ratio by using 3 pass progressive compression, though baseline optimized works pretty well. Choose very low quality levels (e.g. 2 or 3) and experiment until you've found a good trade off.
PNG images are already compressed internally, in a manner that doesn't benefit from more compression much (and may actually expand if you try to compress it).
You can:
Reduce the resolution from 940x940 to something smaller like 470x470.
Reduce the color depth
Compress using a lossy compression tool like JPEG
edit: Of course 250KB is large for a web background. You might also want to rethink the graphic design that requires this.
Caesium is the best tool i have ever seen.