
Fun Photoshop File Format Facts - robin_reala
https://posts.postlight.com/fun-photoshop-file-format-facts-edbc1374c715
======
IvanK_net
BTW. I have spent 3 years studying PSD format while making
[http://www.photopea.com](http://www.photopea.com)

True fun facts are, that Adobe specification [http://www.adobe.com/devnet-
apps/photoshop/fileformatashtml/](http://www.adobe.com/devnet-
apps/photoshop/fileformatashtml/) is very incomplete and that Adobe is not
going to make some data open
[https://forums.adobe.com/thread/1524517](https://forums.adobe.com/thread/1524517)
.

You can ask me questions, if you want :)

~~~
agumonkey
reminds me of the CCC PDF talk
[https://www.youtube.com/watch?v=l6eaiBIQH8k](https://www.youtube.com/watch?v=l6eaiBIQH8k)

lots of .. surprises.

~~~
IvanK_net
PDFs can be inserted into PSD file as a smart object. So we will need to add
PDF support into Photopea in the future. Luckily, there already exists pdf.js
[https://github.com/mozilla/pdf.js/](https://github.com/mozilla/pdf.js/) :)

------
slr555
What is interesting to me is the intersection of all these perspectives about
code and the user experience. I have taken quite a few photoshop classes
through the years from the perspective of a photographer (as opposed to
designer) and what always makes me smile are all the functions you are told
never to use. The most basic of these is the menu choice under Image>Black &
White. When asked why we should not use it the instructor invariably says,
"Photoshop is a monolith of code and Adobe is terrified to remove anything for
fear it will all come crashing down. So even though no one uses Black & White
it will be there forever."

I am told this is much of the reason that Lightroom was born. It was an effort
to make a photographers tool that wasn't crushed under the weight of its own
legacy code.

------
vladdanilov
The fun is multiplied by how Photoshop actually renders graphics. For example,
1-pixel drop shadow looks identical to 2-pixel one. When scripting, bounds of
vector shapes may be off by 1 or 2 pixels due to some floating point math
followed by rounding. Just today stumbled across dithering issues caused by
mismatching user-defined and internal color values
([https://twitter.com/vmdanilov/status/705262877805039616](https://twitter.com/vmdanilov/status/705262877805039616)).

~~~
PeCaN
And there's the fact that its rendering of 1px vector rectangle borders
depends on their location. Yup, sometimes they render a little bit thicker[1],
which can be fixed by moving it up or down a couple pixels. I kind of hate
Photoshop, except it's actually 10x better than anything else at what it
does[2]. RIP Fireworks though.

(As of CS 5.5)

1\. Photoshop does antialiasing/subpixel rendering on vector shapes, so while
"a little bit thicker" is of course 2px, the second row of pixels is blended
with what's nearby.

2\. Haven't tried GIMP for a couple years though. Also I've switched to Krita
for digital painting lately, and actually like it more than PS.

------
emehrkay
Apparently adding a solid white layer as the upper-most layer will sometimes
reduce overall file size.

~~~
Rumudiez
I believe that's because it saves bytes when generating a flattened preview
image which for high resolution PSDs can be quite expensive to do losslessly.
Can anybody confirm?

~~~
MontagFTB
This is likely what is going on. PSDs have a flattened, full-size version of
the image embedded for compatibility's sake.

Instead of a white top-layer you could also disable the "Maximize
compatibility" option when saving the PSD, which will strip out this full size
rendition.

~~~
jzwinck
If you disable Maximize Compatibility you also lose compatibility with current
programs from Adobe itself, such as Lightroom. So while it seems like a good
thing to turn off old crufty stuff, it actually is horrible.

~~~
Rumudiez
I didn't know that Lightroom had that restriction, actually. Is that tested
with CC 2015 versions of both programs?

I do know that Maximize Compatibility doesn't affect usage within Illustrator
and InDesign documents, though, which to me are the more common use cases for
a PSD anyway, so I'll probably stick to unticking that box.

------
Archio
This gives me fond memories of the famous PSD format rant in source code:
[http://codepad.org/DidDsbjF](http://codepad.org/DidDsbjF)

~~~
jkaptur
Maybe it was the article's reprinting of that rant, in its entirety, with a
link to the actual file in github.

~~~
logicrook
Hey, do we have to read the articles before commenting now?

Let's take a stand for free speech! Ill, unadvised speech is still speech!

