 |
Saving pictures, file formats
By  Thomas F Abrahamsson
Index:
Picture compression
First, to know the background, I'll give you some info on computer
pictures:  Without compression, picture files are
huge. This is because a computer picture consist of millions of tiny
little dots called pixels. A normal picture easily consist of over a
million of pixels, and each of these pixels has a colour.
There are three generally used ways of saving pictures:
Uncompressed (non-destructive)
This way of saving images produce files. It simply takes each and
every dot on the picture and saves down the colour value in one, large
queue of pixels. The BMP format found in Windows uses this way of
saving, that's why the BMP files are so big.
(There is a workaround in BMP called RLE, run length encoding. RLE
is a simple compressing algoritm to shrink file sizes a
little. Basically, it find repetitions of similar pixels in the queue
i just mentioned. Instead of writing down 200 red pixels (Like "red
pixel, "red pixel", "red pixel", and so on 197 more times) , it says
'Here are 200 pixels. They are red".) In all cases, this is
non-destructive, which means that the exact picture is saved, and once
you load the picture again, you will get that very same picture back,
each pixel unmodified.
LZ Compressed
LZ is a well known algoritm for compressing data. It's usually very
effective when it comes to written text, and variations of LZ
is used in most popular file compression utilities found, like
ZIP, ARJ and SIT.
GIF and TIFF uses LZ compression for making picture files smaller. The
LZ algoritm is non-destructive, so the picture you get from packing up
a GIF, is exactly the same as you saved down.
Compared to RLE (mentioned above) LZ uses bit trees to pack data more
effective.
Destructively Compressed
JPEG and MPG are examples of destructively compressed pictures. A JPEG
picture is saved in a quite complicate format, which takes in mind the
human eye and perception. Things that are not very visible, are
removed when saving, and then approximately re-generated when
reloading the picture.
Bit depth, short intro
The larger bit depth, the bigger files and nicer pictures.
| Bit Depth | Colours |
| 1 | 2 |
| 4 | 16 |
| 8 | 256 |
| 16 | ~65000 ("High colour", Thousands of colours) |
| 24 | ¨16.7 ("True Colour", Millions of colours) |
Most scan programs produce pictures in 24 bit plans (16.7 million
colours).
JPEG or GIF?
Generally speaking, JPEG is the better option. With some exceptions (see below) a JPEG picture can get smaller and more effective. JPEG is constructed for packing photos and such, so its ideal for painted pictures as well!
If you don't know which to chose, chose JPEG. (See below for hints on how to make effective JPEG pictures)
What about GIF pictures then? Well, these are often used on the web for
a number of reasons. The main ones are:
- Can have transparent backgrounds!
- Can be animated
- Are not destructively saved - good quality.
- Can be small, if the right conditions are met...
At Elfwood, there is no need for transparent backgrounds, so this is right out. If you have an animated scene, you have to chose GIF though, so that one is clear. But what about quality and size then?
Well, if your picture contains only a few, distinct colours you can usually save it as a GIF and gain some size! If your picture is black and white, (lineart) you can also save it as GIF and gain some quality and kB's. So, that's basically it: Black&White line art, and small pictures with few colours. Otherwize, use JPEG for Elfwood. Conclusion:
- If the image has many unqiue colors and has a softer, more photolike, appearance, go for JPEG and save as 'medium' quality.
- If the image has less colours, make a GIF. In photoshop, you
can enter the number of colours to use when you go from RGB to INDEX'ed colour mode. (See the GIF chapter for more info)
- Why not PNG, BMP or TIFF or....?
Simply because I can't handle them correctly, nor can
the majority of the browsers. Convert to JPEG or GIF before you send
me. At Home: You can use any format you want! Remember that most web
browsers only support GIF or JPEG though...
How to make smaller JPEG pictures
If you save and reload a JPEG picture many times, the quality of the
picture will get worse and wose, so NEVER EVER use JPEG as your
working format. This will eventually result in unusable material.
- So, should I ever use JPEG then?
- yes, it is a very effective packing format, which generates very
small, and indeed good looking pictures, for example for the web. In
most cases, JPEG is the best choice. (See chapter below for a discussion on
this topic...)
- What is this "quality factor" then?
- When saving a JPEG, you can actually tell how much data that should
be removed. If you remove too much, the picture might appear a little
blurry and squary at some places. If you remove too little, you will
end up with huge files anyway.
- Why bother about quality anyway?
- Faster downloads (2-3 times faster) for modem users!
- Less disc space used at lothlorien
- So, what image quality shold I have at my JPEG pictures?
- When saving a JPEG, you can chose how much you want to pack it (ie, how much information to remove).
Maximum quality.
Size 27608 bytes. |
'High' quality.
Size 16608 bytes. |
'Medium' quality.
Size 10948 bytes. |
'Low' quality.
Size 8235 bytes. |
| The picture above is © Thomas Abrahamsson |
So, what happens with my picture?
Let us compare the two most extreme cases, the absolute minimum compression (Often called Max quality) and
the most extremely violent compression (Min quality). Normally you use something between those two (Medium quality), I use these two to illustrate the destructive compression though:
(Above) This is the picture saved with minimal compression (max quality), As you can see in the zoomed up area, things are sharp, clear and fine. However, this picture is very very large in KB count: 51 KB.
(Above) This other picture illustrate the worst case scenario with JPEG (Minimum/Low quality). If you look at the zoomed-up area, you will notice that the picture is blurry. This is what JPEG can do to your pictures, if you chose maximum compression. So, use some medium compression value instead, and those blurry areas will not be as visible to the eye as in this example. The only good thing with THIS picture is that its extremely small in KB count: 9 kB (!).
(Above. Finally, This is the same picture examined. This time its saved with a medium degree of
compression. As you can see, Its not very blurry (not visible if not zoomed up like this)
and file size is decent: 21 kB.
So, How do I save a jpeg image in this medium quality then?
That depends on your paint program. Some basic paint programs does not
include this option. However, Paintshop pro (mentioned below) is
avalable for download on the Internet and is recommended!
Here are some examples for three major programs:
Photoshop 3
The above screenshot is taken from Photoshop version 3 on a Windows
Machine. In Photoshop 4 you have more control to change the quality
setting, while version 3 only support these four predefined values.
Paintshop Pro
Quality is called compression level. The paintshop pro manual says:
"Compression Level.
The compression level controls the amount of data compression applied to the image. The higher the number, the smaller the files, and the greater the loss of data. "
- Select image type to "JPEG - JPEG - JFIF Compliant"
- Press the options button
- Lower compression level.
Photoshop 4
Photoshop 4 gives you more control!
David Östman shares some hints:
"I have noticed that when it comes to JPEG and pencil art, you can save
the image using the lowest quality (i.e. highest compression) without
losing any quality or details whatsoever. I use Photoshop 4.0 and chose
Quality 0 (zero), and as far as I can see there is no difference from
10, except for the size of the file.
I once took a GIF pic from the gallery, 101 kB, saved it in JPEG format
in Quality 0, and it ended up as a 36 kB file. I then compared the two
of them, and there was no difference at all. Same quality, same
everything. Just 65 kB smaller..."
Some final notes:
As Jpeg actually modifies the picture, destroying it a little, you
should never work with JPEG pictures. When you do digital painting, or
something like that, always save the picture as TIFF or some other
non-destroying format. If you load and save from a JPEG file several
times it will get more and more blurred... When you are DONE with your
changes, and ready to upload the picture to Lothlorien, first then you
save a copy in JPEG format, and upload that copy (keep the original).
What if I want transparency?
If you want a colour transparent, you have to use the GIF format, as
JPG doesnt support this feature.
How do I check how big the resulting file is?
To see the current file size, you shouldn't look at the file size information in your paint program. This one displays how big the file is WITHOUT any compression at all. You must go to the windows explorer (windows) or finder (mac) and look at the actual file sizes there.
About GIF
First of all, GIF is suitable for line art, and images
with large areas of similarly coloured areas, or with a limited
number of colours. This is due to the way
the GIF standard works. For "photolike" pictures, JPEG is a better
choice. Gif isn't destructive.
In Photoshop, when going from RGB mode (true colour / 24 planes / etc) to INDEXED colour you can specify how many colours the new image should have. The less colours you allocate, the more grainy picture... but, also, less storage size. The smaller the picture, the faster download for all the modem users around. Most GIF's look excellent in just 96 or 120 colours.
In photoshop, it look like this:
(above) We go from RGB mode (which is default) to Indexed colour. This gives us a palette with a fixed number of colours. The RGB picture can contain 16.7 million different colours, so in some way, the paint program has to compensate for this. This is what the dither option tells us. Try the different modes to see the difference. Normally, GIF's pack best if you choose 'none' at the dither option. (see below)
For a table on color depth <-> number of colours, look at the beginning of this article!
...in Paint shop pro, it look like this:
This is about the same as in Photoshop. You chose X colours, and enter (in the box (see below)) how many colours you should head down to:
Marie (valkyrie@earthlight.co.nz) has a useful hint to share:
"I have a useful little hint for those resizing pics with Paint Shop
Pro.. especially those pencil drawings with fine outlines.. instead of
doing a straight resize, I found it much better to go to the image
selection and choose RESAMPLE, choose size specs and that way less
information(detail) is lost! then go and do greyscale(256 shades) and
then decrease colours down from there(I went to >16)! :) (this is for
those saving in GIF format)"
Quality comparison, different No of Colours
Ink and charcoal pictures can be reduced to some 8 or 16 colours without losing any quality. A standard GIF is 256 colours, and going down to 16 makes the file much smaller. Have a look at this normal colour picture first:
256 colours
Size: 28483 bytes |
128 colours
Size: 23141 bytes |
64 colours
Size: 19488 bytes |
32 colours
Size: 15903 bytes |
16 colours
Size: 11863 bytes |
8 colours
Size: 8886 bytes |
| The picture above is © Thomas Abrahamsson |
Apparently, we can go down to 64 or even 32 colours without loosing
too much in visible quality. Note that this is a photo-like colour image which
normally best packed with JPEG. If we do the same thing with a black and
white ink picture, things are even better. Line art type of pictures (as mentioned before) are
very suited for GIF's ability to save in less colours. Just have a look at this example, and see what I am talking about:
 
The first picture is an ink picture saved with 256 colours, this making it 23 kB in size. The second one is in only eight (!) colours, making it 9 kB in size! Can you see any difference? I can't...
About PNG
PNG files nearly always use file-extension "PNG" or "png".
Portable Network Graphics (PNG) is a pixel based image format that
uses non destructive (lossless) compression. It was created to improve
upon and replace the GIF format, as an image-file format not requiring
a patent license.
PNG supports both palette-based (palettes of 24-bit RGB colors) or
greyscale or RGB images.
The motivation for creating the PNG format came in early 1995 when it
came to light that the LZW data compression algorithm used in the GIF
format had been patented by Unisys. Some other problems with the GIF
format also made a replacement desirable, like the limitation to 256
colors.
At the time of writing, Elfwood doesn't support PNG even though we
plan to do it... real soon :)
FARP Article Guestbook
| Date | Name | Comment | | | 11 Dec 2005 |  Anonymous | i want to know how to put JPEG on my computer.how do i do it???????????????// | |
| 30 Mar 2006 | UnderBlueSkys | Many Times after a scan is done or you download something .. the picture is huge in physical size as well as pixels. Sometimes as crazy as 20 x 24 at a high resolution too. For this problem you can resize the physical dimensions of the picture first. Such as ... a 20 x 24 down to a 8 x 10 or even a 4 x 6. Many times that greatly reduces the pixels but is not reducing the quality For internet posting this is all that is needed many times. After you reduce the physical size you can see just what real pixel size is... then you can reduce the pixel size to a resonable one without too much quality lose or the need to crop. Be sure to keep the original in the high quality large size if it is for printing later. .... Even MSN Paint has a physical size changing area UNDER ... Image ... Stretch/Skew!!! They do not use inches but use percentages ... so you have to play with it some to find the size you want. | |
| 19 Apr 2006 | Chatz | i have a Mp3 player and i can only put JPEG pictures on it. but most of the songs i want are in GIF format. is there possibly a way that i can use to change GIF pictures to JPEG format? | |
| 21 May 2006 | AD Jackson | I only have Windows Art *so sad* so how do i resize and get them down to the required limit???? | |
| 14 Aug 2006 | Anonymoose | "i have a Mp3 player and i can only put JPEG pictures on it. but most of the songs i want are in GIF format. is there possibly a way that i can use to change GIF pictures to JPEG format?"
Your songs are in GIF format? Do you mean pictures? You can change GIF to JPEG using Adobe Photoshop (I would tell you the exact way of doing it but I don't have Photoshop on my computer at the minute). You can save a file into GIF or JPEG, but watch the quality of the picture, as mine has a nasty reputation for turning it all sorts of colours. Hope I could help! | |
| 5 Dec 2006 | Anonymous | how do I make a GIF picture into a JPG? | |
| 7 May 2007 | Ulpu Pajari | >>how do I make a GIF picture into a JPG?
Just open it in a picture-editing program and "save as" JPG. | |
| 20 Jul 2007 | vera | To much to read. | |
| 10 Jan 2008 | Pablo Luna | File formats
http://www.fileformat.info/
BMP
http://en.wikipedia.org/wiki/Windows_bitmap
JPG
http://en.wikipedia.org/wiki/Jpg
GIF
http://en.wikipedia.org/wiki/Gif
PSD
http://en.wikipedia.org/wiki/Adobe_Photoshop#Features
PNG
http://en.wikipedia.org/wiki/Portable_Network_Graphics
FREE TOOLS
GIMP (Image editing software)
http://gimp-win.sourceforge.net/stable.html
You need to download and install GTK+ environment and GIMP
Tutorials
http://www.gimp.org/tutorials/
3D TOOLS
Anim8or (3D modeller)
www.anim8or.com
Tutorials for newbies:
Lesson 1
http://www.orbithangar.com/searchid.php?ID=2729
Lesson 2
http://www.orbithangar.com/searchid.php?ID=2730
Lesson 3
http://www.orbithangar.com/searchid.php?ID=2731 | |
| 10 Mar 2008 | Vera Franks | What type of disk do you use to make copies of you pictures? I am very new at this and have tried to save on a CD and a DVD. I get messages saying ’cannot be saved on this disk’ So what kind do you use, there are so many out there I need someone to tell me exactly what I need. Thanks, Vera | |
| Page: [1] 2 3 4 5 6 7 |
 Back to the FARP main page.
 The collection of art and writing tutorials in the Elfwood Fantasy Art Resource (F.A.R.P.) is a part of Elfwood.
The FARP logo was created by  Miguel Krippahl (The muscular guy in the FARP-logo) and  Thomas F Abrahamsson (The text and general graphic design). Those sections written by volunteers are copyrighted to Thomas Abrahamsson and the respective writer. Elfwood is a project created by Thomas Abrahamsson. All rights reserved. Unauthorized Reproduction of the graphics, writings, and materials on these pages is absolutely prohibited! You may consider all material on these pages protected and copyrighted, unless otherwise noted. You may NOT use the images found at the FARP or Elfwood pages on your home pages! All of these images are copyright protected! Everything you see here represent the collaborative effort of the Elfwood community and Thomas Abrahamsson. Please read the Legal Disclaimer for more info on warranties/etc for these pages!
|
|
