With the release of IE 7, the consistent use of PNG for Web sites and Web applications moved closer to a reality. However, while recently experimenting with a few concepts that rely heavily on PNG, I discovered IE interprets the gamma (gAMA) data chunk contained within a PNG differently than other browsers. The image will render darker(i have encountered with it,and it takes me some time to fix it.), which can be problematic if you need a GIF or JPG to match the color profile of a PNG.
The W3C specification pinpoints the gamma and chromaticity data associated with a PNG as the primary advantage of this format, since it is a mechanism for more accurately managing colors across different platforms. Yet, it is the PNG alpha transparency that gives Web developers an opportunity to extend the design pallet. Unfortunately, in order to take advantage of one, it is necessary to compromise the other, and therefore, the gamma data should be removed.
TweakPNG is an amazing program for accomplishing this task. It is available under the GNU GPL, and is free to use. You can download it by clicking here. According to the Web site, the program has not been updated for a few years, but it works on Windows 95, 98, ME, 2000, and XP. Open up your PNG with TweakPNG, highlight the gAMA row under the Chunk column, right-click, and left-click on Delete. Now save the PNG, and the issue is resolved.
Choosing an image format
- For photos and scans JPEG will almost always be more compact than 24 bit PNG format.
- For true color images containing text and sharp color transitions 24 bit PNG could turn out smaller, and will certainly provide the best quality. Ideal for maps, charts and diagrams with more than 256 colors.
- If the quality is acceptable, converting true color images to a 8 bit palette can often produce a smaller file. Dither the colors if necessary.
- For converting GIF images, use 8 bit PNG. With the right image tools only tiny GIF files remain smaller than a PNG equivalent (small icons, for example).
- Use single-color transparency if alpha-channel transparency is not really necessary. It works in Internet Explorer and the file size will most likely be smaller.
- There’s a small overhead for PNG’s versatility: the minimum file size is 67 bytes for an opaque single pixel.
