PS7 and Linear PNG?

[Roger_Cavanagh]

Here's something I stumbled across today that I thought I'd share.

I fired up the latest version of BreezeBrowser (2.0.1) today and converted a single image to (so I thought) linear TIFF. Going into PS7, I used File Browser to open the image and realised that it was a PNG image. Checking with the BB release history, I found that Chris B has added support for 8 and 16-bit PNG format. Checking some web sites, I read:

PNG provides a patent-free replacement for GIF and can also replace many common uses of TIFF. Indexed-color, grayscale, and truecolor images are supported, plus an optional alpha channel. Sample depths range from 1 to 16 bits... PNG is robust, providing both full file integrity checking and simple detection of common transmission errors. Also, PNG can store gamma and chromaticity data for improved color matching on heterogeneous platforms.

So I run HQ Chooser. Everything seems to be fine.

AS often happens, the PS manual didn't throw any further light. I haven't tested exhaustively, but so far it appears that 16-bit linear PNG can be used as a replacement for linear TIFF. The big advantage of using it is space: the PNG file is around 10mb compared to 18mb for TIFF. There also is a speed improvement reading the file in PS and in Windows Explorer.

Two other points: PS6 seems to be capable of reading only 8-bit PNG and PS7 will only write 8-bit.

Anyone got anything to add?

Regards,

[Pekka]

PNG seems to be good format - only reservation I have is how supported it will be in let's say 5 years. Industry has adopted TIFF so it'll be very likely that we have TIFF in all future programs. TIFF has also lossless compression options but at least LZW compression has a tendency to save it larger than the original (!).

One other thought: I recall that once Photoshop had a lossless compression choice in PSD format (or am a dreaming?), now it seems to do it always uncompressed. I can't understand why Adobe has not included a lossless compression option in new Photoshop's PSD's..

[rudison]

There is a free plugin available for Photoshop that supports the 16 bit PNG format: SuperPNG. See http://www.fnordware.com/

It replaces the default import/export filter of Photoshop and is available for Win & Mac.

It tried it with PS7. It works with RGB and grayscale images (with or without an alpha channel). The compression is even a bit better than the default PNG filter (tested with 8 bit images). Saving a 8 bit PNG file is more than twice as fast a the default PS filter. The resulting file seems to be valid: All the graphic programs i tried had no problem in opening the file created by SuperPNG.

Advantages of PNG:
- very good (lossless) compression
- open source format and patent free
- supported by nearly every image editor / viewer
- no compatibility problems (unlike compressed tiff)

Disadvantages of PNG:
- Currently doesn't store EXIF information and ICC profiles within the file (as far as I know)
- Saving a PNG file takes longer than saving an uncompressed file