I would like to know which image format inside PDF's is rendered fastest. I tested mupdf code and I figured out that image decoding takes an important part in rendering time. So I would like to know if there are image formats that would not impact very much on cpu load.
I dont think this is really a question of what is best simply within PDFs, however:
As a general rule, I have always found that pre-rendering the image's size to the actual size you wish to present on screen is the best way to get both size and rendering speed to what you want them to be. Simply dragging an image into a document doesnt bring the pixel count (thus size) down as most document types simply put a display size tag around the full image. This causes the display program to have to real-time resize the image for display. The less the display program has to real-time resize the image the faster it will display.
As for file types:
Bitmaps are generally considered the fastest to display as they (for the most part) are copy and paste the color for each pixel onto the screen pixel. They are generally considered the biggest file. Depending on your images, if they aren't noisy (have a lot of solid runs of the same color) then they can be RLE encoded. I have seen many RLE encoded images that are indeed even smaller than JPEG images, but it is very situational.
JPEGs tend to be the smallest for transfer and also generally display decently quick. As an opinion they are also the lowest quality images (look close, if you started with a perfectly clean image, JPEG compression will add noise to it unless using lossless compression)
PNGs tend to be my favorite. They can be lossless compressed, can be fairly small if using flattened PNGs (i.e. NOT ADOBE FIREWORKS PNGs) and do produce crisp images that render fairly quickly.
So to sum up: I would probably recommend flattened PNGs that have been pre-sized and saved to the size you wish to display on screen.
Related
Pretty much with every Pagespeed test I do for all my website I get the comment "Optimize images by lossless compressing image X" which often increases my page rank a lot.
I already save EVERY image with 'save for web' with Photoshop, but I was wondering how I could "Optimize images by compressing lossless" even more. As far as I know I'm already doing everything I can.
Really wondering..
Off-topic, but I noticed that Google's PageSpeed uses a Retina device to check, since all my Retina images got loaded instead of the regular ones. Since these are larger than the area I got a 1/100 score on the mobile segment. Haha.
This was a real issue with many of my sites, however I use the free version of kraken to 'loosely compress' all of my images and this passes the Google Test, thus boosting rankings!
https://kraken.io/web-interface
I must have used this for well over 10,000 images already!
The images you create in programs like Photoshop and Illustrator look amazing but often the file sizes are very large. This is because the images are made in a format that makes them easier to manipulate in different ways. If you put these files on your website it would be very slow to load. Optimizing your images for the web means saving or compiling your images in a web-friendly format depending on what the image contains.
How does it work?
There are two forms of compression that we need to understand, Lossy and Lossless.
Images saved in a lossy format will look slightly different than the original image when uncompressed. Keep in mind that this is only visible at a very close look. Lossy compression is good for web, because images use a small amount of memory, but can be sufficiently like the original image.
Images saved in lossless format retain all the information needed to produce the original image. For this reason, these images carry a lot more data and in return are a much large file size.
We also can optimize images for the web by saving them as the appropriate dimensions. Resizing the image on the webpage itself using CSS is helpful but the issue is the web browser will still download the entire original file, then resize it and display it.
Can you imagine taking a poster size image and using it as a thumbnail? The little 20px by 20px image would take as long to load as the original poster when we could just be loading a 20px image the whole time.
How to Optimize Images?
In simple terms optimizing your image works by removing all the unnecessary data that is saved within the image to reduce the file size of the image based on where it is being used in your website. Optimizing images for the web can reduce your total page load size by up to 80%.
Full optimization of images can be quite an art to perfect as there are such a wide variety of images you might be dealing with. Here are the most common ways to optimize your images for the web.
Reduce the white space around images – some developers use whitespace for padding which is a big no-no. Crop your images to remove any whitespace around the image and use CSS to provide padding.
Use proper file formats. If you have icons, bullets, or any graphics that don’t have too many colors use a format such as GIF and save the file with lower amounts of colors. If you have more detailed graphics then use JPG file format to save your images and reduce the quality.
Save your images in the proper dimensions. If you are having to use HTML or CSS to resize your images, stop right there. Save the image in the desired size to reduce the file size.
To resize your images you will have to use some form of program. For basic compression, you can use a simple editing program such as GIMP. For more advanced optimization you will have to save specific files in Photoshop, Illustrator, or Fireworks.
I'm porting some CF 2.0 VB.Net apps to a newer version of a handset that has twice the screen resolution. So I have to double the dimensions of everything otherwise it all gets squished up into the top LH corner of the screen.
One screen had a bitmap which was 250K in size, and after I doubled the dimensions naturally it blew out to one MB. This isn't real good on a handheld, so I fired up irfanview and converted it to a .GIF. The .GIF was only 60KB in size, with no discernible change in the quality of the image.
To me, it seems a no-brainer : Convert all Bitmaps to Gif (or JPG) and get the same results for a fraction of the disk space (and probably quicker form loading times).
But does anyone know of a situation where you would use a bitmap in preference to a GIF/JPEG? I cannot find any.
I really can't think of any realistic example where you would prefer an bitmap to a GIF. Since GIF is a lossless format you loose no information when storing images. So after reading the file in your app you will have the same image data as if you have read a bitmap. And like you said: The file will be smaller and thus will probably will be read faster from disk.
JPEG is different because it's a lossy format, meaning you will lose information when storing images in it. You will need to decide if the loss of information is meaningful in your app.
Bitmaps would be preferable if and only if reading files from disk where faster than decompressing the file in memory.
And to be precise you would prefer bitmaps when storing images in main memory, so you can work easily on the data in your code. Which is actually what you most likely already have when you have loaded a file using an image library.
To cut a long story shorts, a BMP is stored as a series of pixels along with their colour. This is useful if you want to do such things as pattern recognition, movement detection and such like.
Bitmaps are typically used for their convenience - you can knock one up in paint without having specialist graphics software.
What is the best way to store images for web-sites?
What size I should not exceed?
Now, I save all interface-files in png (mostly in sprites) and usual images in jpg's. Some images are about 100-150Kb.
What quality and compression should I choose while saving images?
Preparing Images
To prepare images for presentation on
the Web, follow these steps:
Begin a new file. If it’s a photo or original artwork, use 300 dpi as
the resolution. If you are creating
something simple, set the resolution
to 72 dpi.
Use the drawing, text, shape and other tools provided in the graphics
program to create your image.
Save your file in the native file format (a file type meant for editing
that is specific to the image editing
program) of the program you are using.
For example, a Photoshop document
creates files with a ".psd" extension.
If you need to make a change or edit
later, do it in this file rather than
on the Web.
If necessary, lower the resolution of the image to 72 dpi.
If necessary, resize the image to the height and width in pixels
specifications desired.
Save the file in a Web-ready file format, usually a GIF (most programs
give you several choices for file
types), finding a balance between the
way the file looks and an appropriate
file size. Some image programs will
let you preview the final file output,
whie in others, you have to save it
and load it in the browser to see the
final effect.
Preparing Photographs
To prepare photographs for
presentation on the web, follow these
steps:
Download the photo from your digital
camera or scan in the photograph. The
process for this varies depending on
the software bundled with your scanner
or camera. The image will probably end
up in "Your Photos" on Windows, or the
"Photos" folder on a Mac, unless you
chose some other folder as the default
destination.
Use the color correction, drawing, text, shape, and other tools provided
in the graphics program to alter and
improve your image.
Save a copy of your file in the native file format of the program you
are using. Make later changes or edits
in this file rather than on the web.
With photographs, save an untouched
version of the photo in case you want
to use it again for another purpose.
If necessary, lower the resolution of the image to 72dpi.
If necessary, resize the image to the height and width in pixels
specifications desired.
Save the file in a web-ready format, usually a JPEG, finding a
balance between the way the file looks
and an appropriate file size.
Making images web-ready is all about
compromise. In general, the better
your image looks, the larger the file
size will be. The larger the file
size, the longer it will take to
download. Your job is to find a
compromise between quality and file
size. Some things to consider are:
Is this image conveying crucial information? If so, go for higher
quality.
Is the image on a page with a lot of other images? If so, make the file
size smaller.
Will your web visitor be able to detect that the quality of a photo or
image isn’t very good?
Make images of people fairly high quality because visual acuity is
strongest with people’s faces.
(Source)
For your images, here is a tip:
Do not scale images in HTML
Web page designers sometimes set image
dimensions by using the width and
height attributes of the HTML image
element. Avoid doing this since it can
result in images being larger than
needed. For example, if your page
requires image myimg.jpg which has
dimensions 240x720 but displays it
with dimensions 120x360 using the
width and height attributes, then the
browser will download an image that is
larger than necessary.
(Source, see another tip)
This all depends on what the image is for. If you're generally adhering to a web-safe palette, gifs will come out smaller and clearer than a jpeg. Jpeg's are for photos. For jpegs to handle websafe colors well, you need to save at 88%+ quality, which increases file size. Png's generally have the best quality, and in some cases (when you don't need transparency) can come out smaller than jpgs, and comparable to gif. So, for jpeg photos, 80 quality, (sometimes even 75 for smaller images) will get you decent results and small filesize. Use gifs / png for site imagery generally. As far as images on a page, I try not to exceed 30kb total, assuming the page isn't something that is focused on photos / imagery. Hope this helps.
It depends on what your image is of, and what the quality needs to be, whether you choose quality over page loading etc.
I personally save all mine in .png but IE has a problem rendering the colour correctly in .png so if you are using them for aestetical purposes I would save .jpg
As to the size of the image, like said it depends really on the quality you want your image and how it affects performance if it is a large file.
i usually use save for web mode that exists in photoshop. obviously the lower size is best. The sizes that you talking about (100-150) are good or not in relation to the dimension of the image. Anyway i advice you to use sprites and when possible in jpeg format.
something like 75-80% quality are good enought to a good quality of image
And please pay attention to the cmyk mode, that cause problems in some browsers
I have a small script that I use to resize all of the images in a directory. I run this script in cygwin and it uses "convert" to do the image resizing. The images change their resolution just fine, but I am having problems with file sizes after the script is run.
I typically use this script to resize images dumped out from a Powerpoint presentation to use in a little web presentation app that I wrote. When I dump out gif's and run the script, the files more than double in size (ex. 8KB to 18KB; 14KB to 50KB)
The pertinent lines of the script are as follows:
/usr/bin/convert $holdfile -thumbnail x480 temp.GIF
mv temp.GIF $i
Is there a switch to prevent the file sizes from growing so much? I know that the file sizes are not huge, but when I have a good number of people connecting to a presentation or the unavoidable dialup users, I just want to make their experience as nice as possible.
Edit: I should have specified that the files start at a 960px x 720px resolution and are being resized to 640px x 480px.
Well, this can happen if convert compresses worse than the input files. Since the exact same compression scheme might yield different results depending how good the compressing code is this can happen.
Another, more likely option here would probably be that you are resizing the images which will probably be done with bicubic resizing. This causes the edges of text or drawings to become a little bit blurry. This means they use up more colors and compress worse.
Also likely would be that your original images use an optimized color palette, maybe just with a few colors and after resizing they need the full 256 colors which are supported by a single GIF frame, due to smoothing done by the resizing.
In any case, you probably should see better performance using PNG instead of GIF. PNG was designed as a modern replacement for GIF and no (graphical) browser in use today has problems displaying PNGs (without an alpha channel). PNG compresses much better than GIF, and allows more colors at the same time. Also there are tools like optipng which will compress PNG images even further.
Convert automatically optimizes the palette however the palette might be growing due to colors being blended during resize. You should be able to inspect the source and resultant images in a graphics program and see the number of colors.
GIF only supports LZW compression but due to patent restraints that have since expired (the last was 2004) it was once necessary to manually enable LZW compression. I'm not sure if that is still the case however it's worth looking into.
If LZW compression is specified but
LZW compression has not been enabled,
the image data is written in an
uncompressed LZW format that can be
read by LZW decoders. This may result
in larger-than-expected GIF files.
- imagemagick.org
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.