Subject: [VCARDDAV] There should be suggested PHOTO dimensions

From: "Peter K. Sheerin" <[email-masked]>
Date: Thu, 20 Mar 2008 18:26:53 -0700

Since the purpose of the PHOTO field is to include a photo of the 
person, and different aspect ratios and sizes accomplish this to a 
greater or lesser extent, the specification should provide some guidance 
on the matter.

The only existing guidance I have found is from the Jabber group, which 
suggests square, instead of portrait, photos and a maximum photo size 
(max 64 px and preferably less) that I believe is too little to provide 
an adequate representation.

Since most users will want to use a head shot, and such portraits are 
generally rectangular, the vCard specification should provide some 
guidance here so users and software authors know what ranges should be 
provided and supported.

Given the international nature of contact exchange these days, the 
dimensions should be based on ISO 216, the international paper format, 
which specifies a ratio that is consistent across all sizes, and thus 
makes it possible to scale documents without cropping or creating the 
letterbox effect.

When I first created a fancy vCard years ago, I did something like this 
based on U.S. photo dimensions, and came up with this list: 50x70, 
75x105, 100x140, 150x210, and 120x250, but these don't quite represent 
the ISO 216 ratio of 1:√2 (http://en.wikipedia.org/wiki/ISO_216).

So instead, I'd like to suggest this recommended size, which is taken 
from a pixel interpretation of ISO 216 
(http://en.wikipedia.org/wiki/Metric_Pixel_Canvas):
dA8: 208 × 296

This can be reduced in even multiples to create images of 104 × 148 and 
52 × 74. By suggesting these sizes, aspect ratio can be maintained and 
the scaling algorithm can be simple enough it's unlikely to be an issue 
on mobile phones or PDAs and will result in acceptable image quality, 
unlike scaling in non-even increments.

208 × 296 is large enough that it should satisfy anyone that wants a 
largish photo to appear (contact management software on a desktop 
computer could benefit here) but still small enough that a moderately 
compressed photo won't be too many bytes.
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