he features for PNG are intended to address the needs of applications that previously used the special strengths of GIF.

• 100% Lossless Compression
  PNG has a better compression than the GIF/LZW method. Like a GIF, a PNG file is compressed in lossless fashion (meaning all image information is restored when the file is decompressed during viewing).
     PNG also allows the creator make a trade-off between file size and image quality when the image is compressed. Typically, an image in a PNG file can be 10 to 30% more compressed than in a GIF format.
  
• True Color Images Up to 48 Bits per Pixel
  PNG supports true color images. True color is the specification of the color of a pixel on a display screen using a 24-bit value, which allows the possibility of up to 16,777,216 possible colors. PNG supports up to 48 bits per pixel allowing it to double the possibility of 24-bit value. Many displays today support only an 8-bit color value, allowing up to 256 possible colors.
     There is no other widely used image format that losslessly compresses true color images as effectively as PNG does.
• Gray Scale Images Up to 16 Bits per Pixel
  Asides from being able to support true color images, it can also be saved using a gray-scale format. Regularly, displays only support 8-bit gray scale value. PNG supports up to 16-bits.
  Note: Since PNG supports up to 48-bit true color or 16-bit grayscale, saving, restoring and re-saving an image will not degrade its quality.
• Full Alpha Channel and Transparency Support
  Some form of transparency control is desirable for applications in which images are displayed against a background or together with other images. GIF provided a simple transparent-color specification for this purpose. PNG not only supports a simple transparent color specification, but it also supports a full alpha channel as well as transparent-color specification. (The extra byte, called the alpha channel, is used for control and special effects information.) This allows both highly flexible transparency and compression efficiency. Not only can you make one color transparent, but you can control the degree of transparency (this is also called "opacity").
• Streamability and Progressive Display
  GIF is well adapted for online communications because of its streamability and progressive display capability. PNG shares those attributes also.
• Interlacing
  Interlacing is a method of progressive display. This method of progressive display is supported by PNG, and is faster in developing than in the GIF format. Progressive display meaning that while you're downloading a picture, fragments of the picture will be shown as opposed to waiting for the whole image to be downloaded before you can see anything.
• Gamma Correction
  Gamma correction basically refers to the ability to correct for differences in how computers (especially computer monitors) interpret color values. If an image is prepared on a machine with one gamma value and displayed elsewhere, it may look either too pale or too dark; washed out or over-saturated; and will have significant color casts. This feature of PNG allows you to "tune" the image in terms of color brightness required by specific display manufacturers.
• Hardware and Platform Independence
  The format can be accepted by all hardware platforms.

• Single-Image Format
  The one major disadvantage of the PNG is that it is a single-image format. Unlike the GIF89a, the PNG format doesn't support animation since it can't contain multiple images. However, the PNG is described as "extensible." That means Software houses will be able to develop variations of PNG that can contain multiple, scriptable images.
• Slow Acceptances of PNG
  Although PNG has been out for a several years already, it still isn't widely used. There are two reasons for this slow acceptance. The most important is browser support. PNGs are supported in Netscape Navigator/Communicator v 4.04 and later and in MS Internet Explorer v4.01 and later. Many people have not upgraded to these browsers yet, for any number of reasons. Until the vast majority of web-surfers is using PNG-capable browsers, web developers will be distrustful of them.
     For people who don't yet have PNG-capable browsers, there are plugins, which allow PNG images to be viewed. Some of those know plugins are PNGLive plugin available from Seigel & Gale, and several other image plugins, including Apple's Quicktime, which can also view them.
     The other problem-solving acceptance of PNG is poor implementation in image editing programs. Paint Shop Pro is considered one of the pretty good image editing programs that can handle PNG, but it does have two important defects - palette size and palette transparency inefficiency. When saving an image with 17 to 255 colors, Paint Shop Pro will write a complete, 256-entry palette. This causes the PNG to have from 3 to 717 extra bytes, which will outweigh the compression efficiency that PNG has over GIF in small images.

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