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I've been doing some research to try to figure out why more people do not store high-resolution image files as PNG-24. PNG has exactly-reversible, lossless compression, it is a net-friendly format so any web browser can view it, and it supports full transparency.

I've seen several people say that TIFF has a "higher quality" than PNG, but no one provides any details on exactly how it is of higher quality. PNG-24 is lossless, so when you "Save As" a TIFF to a PNG, how exactly are you losing quality?

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Define higher quality. Does loosing color profile means lower quality? Loosing metadata? Sharpness? Color depth? –  takeshin Jul 11 '11 at 11:27

3 Answers 3

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You explicitly mentioned PNG-24 - that has eight bits per channel, whereas a TIFF file can have 16. That would be one reason the quality could be higher, from a RAW conversion especially but also if you are doing a lot of editing.

The PNG standard also supports 16-bits per channel (PNG-48) but I don't know how many applications support that, whereas pretty much anything that can read TIFF is going to be able to read a 16-bit TIFF file.

TIFF can also store layers in it, which is not a quality issue so much as a flexibility thing. PNG is really meant to hold an image, not a layered set (although APNG can hold a set, it's really not for the same purpose).

One additional bit of practical information is that TIFF can store many kinds of Photoshop layers, I have used it for images which had a number of adjustment layers applied. That is not possible with PNG, you would have to flatten the whole image.

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In fact, channels in TIFF files can be in any IEEE 754 floating-point format too, including the 128 bit one, for 384 bits (48 bytes) per pixel in the RGB, YCbCr and CIE L*a*b* formats and 512 bits (64 bytes) per pixel in the CMYK format. Same applies to any alpha channel, if present, as well as potentially non-visible channels (satellite images are often full of IR channels in different bands, for example). –  Martin Sojka Jul 27 '11 at 11:13

Take a look at Why don't most cameras support PNG format? for some other answers. Often cited reason is that the usual metadata (IPTC and EXIF of TIFF and JPG) is not very well supported by PNG and the software.

PNG does support color profiles now, but it does not offer CMYK as TIFF does, because it is focused on web-usage.

Anecdotal: I used to store 2000dpi 135er scans as PNG before I cared about metadata but the results differ not that much from TIFF with LZW+Prediction (free since 2003) in most of my cases (+25 - 50% size) that it is worth the time converting now.

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PNG as a format has no problem supporting metadata. The problem seems to be with editors and unskilled programmers that assume it can't be done so don't offer it. –  James Snell Aug 13 '13 at 22:07

You are not losing any quality. It is mostly a habit, I am guessing. Lots of books on digital imaging still suggest TIFF as the highest quality format. For non-technical people, that is all they need to know.

Note both TIFF and PNG have higher bit-depths as well. Most people who still save in TIFF use 16-bits per-pixel, so the equivalent of PNG-48. If they save as PNG-24 in this case, they do lose quality.

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What about the metadat issue? –  mattdm Jul 11 '11 at 2:24
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Metadata has no impact on image quality but yes, that is a reason to use TIFF over PNG. –  Itai Jul 11 '11 at 5:15
    
I think that's an important part of the full question, which is only partly about quality and partly about "why would people prefer tiff?". –  mattdm Jul 11 '11 at 9:56

protected by John Cavan Aug 21 '13 at 18:07

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