Every picture tells a story – or does it? Are your website’s images optimized for all people and devices?
When you convert your PNG files, your meta data and keywords are stored inside. The Portable Network Graphic format was created in 1995 when Unisys and CompuServe officially announced that programs using GIFs would require royalties because of the patent on the LZW compression method using GIF.
The best thing about PNG files for digital photographers is that they can be smaller in file size and preserve transparency. PNG’s have proven to be the best for gradients. You can categorize and add keywords. The danger is that there is a problem with the loss of your meta data when the image is opened with indifferent software. Your information can easily get lost.
Comparison to JPEG
JPEG (Joint Photographic Experts Group) format can produce a smaller file than PNG for photographic (and photo-like) images, since JPEG uses a lossy encoding method specifically designed for photographic image data, which is typically dominated by soft, low-contrast transitions, and an amount of noise or similar irregular structures. Using PNG instead of a high-quality JPEG for such images would result in a large increase in filesize with negligible gain in quality. By contrast, when storing images that contain text, line art, or graphics – images with sharp transitions and large areas of solid color – the PNG format can compress image data more than JPEG can, and without the noticeable visual artifacts which JPEG produces around high-contrast areas. Where an image contains both sharp transitions and photographic parts, a choice must be made between the two effects. JPEG does not support transparency.
Because JPEG uses lossy compression, it suffers from generation loss, where repeatedly encoding and decoding an image progressively loses information and degrades the image. Because PNG is lossless, it is a suitable format for storing images to be edited. While PNG is reasonably efficient when compressing photographic images, there are lossless compression formats designed specifically for photographic images, lossless JPEG 2000 and Adobe DNG (Digital negative) for example. However these formats are either not widely supported or proprietary. An image can be saved into JPEG format for distribution so that the single pass of JPEG encoding will not noticeably degrade the image.
The PNG specification does not include a standard for embedded Exif image data from sources such as digital cameras. TIFF, JPEG 2000, and DNG support EXIF data.
Early web browsers did not support PNG images; JPEG and GIF were the main image formats. JPEG was commonly used when exporting images containing gradients for web pages, because of GIF’s limited color depth. However, JPEG compression causes a gradient to blur slightly. A PNG file will reproduce a gradient as accurately as possible for a given bit depth, while keeping the file size small. PNG became the optimal choice for small gradient images as web browser support for the format improved.
Comparison to JPEG-LS
JPEG-LS is a “near-lossless” image format far less widely known and supported than the other lossy JPEG format discussed above. It is directly comparable with PNG. On the Waterloo Repertoire ColorSet, a standard set of test images (unrelated to the JPEG-LS conformance test set), JPEG-LS generally performs better than PNG, by 10–15%, but on some images, PNG performs substantially better, on the order of 50–75%. Thus, if both of these formats are options and file size is an important criterion, they should both be considered, depending on the image.
Comparison to TIFF
Tagged Image File Format (TIFF) is a format that incorporates an extremely wide range of options. While this makes TIFF useful as a generic format for interchange between professional image editing applications, it makes adding support for it to applications a much bigger task and so it has little support in applications not concerned with image manipulation (such as web browsers). It also means that many applications can read only a subset of TIFF types, creating more potential user confusion.
There is a TIFF variant that uses the same compression algorithm as PNG uses, but it is not supported by many proprietary programs. TIFF also offers special-purpose lossless compression algorithms which can compress bilevel images (e.g., faxes or black-and-white text) better than PNG’s compression algorithm. I need to find out more about why we would use TIFF files and plan to find out in an upcoming class.
Bitmap graphics editor support for PNG
The PNG format is widely supported by graphics programs, including Adobe Photoshop , Corel ‘s Photo-Paint and Paint Shop Pro, the GIMP, GraphicConverter, Helicon Filter, Inkscape,IrfanView, Pixel image editor, Paint.NET and Xara Photo & Graphic Designer and many others. Some programs bundled with popular operating systems which support PNG include Microsoft’s Paint and Apple’s iPhoto and Preview, with the GIMP also often being bundled with popular distributions.
Adobe Fireworks (formerly Macromedia) uses PNG as its native file format, allowing other image editors and preview utilities to view the flattened image. However, Fireworks by default also stores meta data for layers, animation, vector data, text and effects. Such files should not be distributed directly. Fireworks can instead export the image as an optimized PNG without the extra meta data for use on web pages, etc.
File size and optimization software
Compared to GIF
Compared to GIF files, a PNG file with the same information (256 colors, no ancillary chunks/metadata), compressed by an effective compressor will normally be smaller than GIF. Depending on the file and the compressor, PNG may range from somewhat smaller (10%) to significantly smaller (50%) to somewhat larger (5%), but is rarely significantly larger for large images. This is attributed to the performance of PNG’s DEFLATE compared to GIF’s LZW, and because the added precompression layer of PNG’s predictive filters take account of the 2-dimensional image structure to further compress files; as filtered data encodes differences between pixels, they will tend to cluster closer to 0, rather than being spread across all possible values, and thus be more easily compressed by DEFLATE. However, some versions of Adobe Photoshop, CorelDRAW and MS Paint provide poor PNG compression, creating the impression that GIF is more efficient.
What is GIMP?
The (GNU Image Manipulation Program) is an image retouching and editing tool and is released under the GPLv3 license as free and open-source software. There are versions of GIMP tailored for most operating systems including Microsoft Windows, Mac OS X and Linux.
GIMP has tools used for image retouching and editing, free-form drawing, resizing, cropping, photo-montages, converting between different image formats, and more specialised tasks. Animated images such as GIF and MPEG files can be created using an animation plugin.
The developers and maintainers of GIMP have a product vision for GIMP to strive to be a high end free software graphics application for the editing and creation of original images, photos, icons, graphical elements of web pages and art for user interface elements.
GIMP’s fitness for use in professional environments is regularly reviewed; as such, GIMP is often cited as a possible replacement for Adobe Photoshop. The maintainers of GIMP state that GIMP seeks to fulfill GIMP’s product vision rather than seek to replicate the interface of Adobe Photoshop.
The user interface of GIMP is designed by a dedicated design and usability team. This team was formed after the developers of GIMP signed up to join the OpenUsability project. A user interface brainstorming group has since been created for GIMP, where users of GIMP can send in their suggestions as to how they think the GIMP user interface could be improved.