dipityPix app

Monday, October 12, 2015

New iPhone app up

We've just updated our main iPhone photo editing app, Subjective, to include reworks of our most successful filters.   It uses a new color space we've developed that I will post more on later this week.

We'll be updating the UI to our new design, but the basic flow and the filters we provide will stay the same.

Please go buy or update the app for $2.99 and RATE IT.   I'll buy you a beer when show me the app on any phone :)   This  is what I am up against, so I need your help.

Tuesday, September 29, 2015

A drawing package with barycentric interpolation?

I want to do a simple diagram that I could easy do with SGI IRIS Showcase (my all time favorite drawing package that as far as I know is extinct).   One feature it had was you could assign three colors to the three triangle vertices and it would interpolate a between the vertices (Gouraud interpolation, barycentric interpolation, linear interpolation, whatever you want to call it).   As far as I know, no current programs support this.  PLEASE tell me I am wrong, or go write it :)

Sunday, September 13, 2015

My new main email address

I have been using shirley@cs.utah.edu (where I worked 7 years ago!) for some time because of the good graphics history karma of the name, the department has been kind enough to leave my account there, and because the systems support at that department is outstanding.   And because my gmail idea sucks-- I can barely spell my middle name!   My computer went into the shop for a week so I've been taking care of some of those non-urgent things on my to-do list and one of them is finding a more permanent email address.  Gmail is the default pick for most people and I like it myself but almost every account name I have tried is taken.

I dug deep into my naming history, and recall that an old FORTRAN trick to keep to 8 letters (a requirement on some systems!) was to eliminate vowels.   English has almost no information in the vowels so this works pretty well.   In my name is "y" a vowel?   I say yes, because it does allow one available email.   Thus my new "permanent" email is now:


If I'm in your address book please update it!

Wednesday, September 9, 2015

A killer app for the new iPad and stylus

Unlike the ghost of Steve Jobs, I am super-excited about the new huge iPad with pencil (or "stylus" for English speakers).   There are surely plenty of art apps that will be great on this device, but for me the killer app will be white-boarding.   At NVIDIA I used shared white boards a lot and my far-seeing boss had me try a wacom cyntiq. 

It was awkward because of clunky software (not wacom's-- the shared whiteboarding software), but wacom had the hardware nailed.    It was a good enough experience I felt like I saw the future.   I have been using the new shared whiteboarding app from limnu and really like it-- I use it to take quick notes on my phone when I am without a pencil.   But my finger is big, and the phone is small.   This shows how much I can get using that:

A screen shot from the limnu app on an iPhone 6+
 It's very usable on the iPad mini (I have posted those on the blog before) and I far prefer it to a "real" drawing program when just messing with ideas.   I have been hoping the Windows 8 tablets would take off because their hardware is great (and so is Windows 8 on mobile-- I loved my windows phone!  I am still wondering why it didn't).  But the new iPad and stylus will make this app perfect for me!   The size is something like we see in real portable whiteboards like this 8.5" by 11" one.   And it looks like the Apple stylus will give finer control than most real white board markers.

It's cool that there is still hardware that can invented that I can hardly wait for!

Monday, August 31, 2015

sRGB gamma

In my previous post I did some gamma conversions to sRGB and a comment asked if I used the real sRGB gamma.   I did not.   From wikipedia the full formula is:


The linear part is only near the beginning (I think to avoid the infinite slope at 0).   I usually just use gamma = 1/2.2 as an approximation, but I thought I better check how much error that introduces.   For the part far from zero, the error is very small:

Nearer zero it's worse but as long as your range isn't in there gamma 1/2.2 is good enough for most things

Wednesday, August 26, 2015

Saturated colors look brighter than greys

Graphics people are pretty used to converting RGB colors to "luminance", and usually things that have higher luminance look brighter.    For sRGB the standard formula is:

Y = 0.2126 R + 0.7152 G + 0.0722 B

The (R,G,B) here is linear.   To get it linear you need a gamma of approximately 2.2 (see the wikipedia page for the exact transform which is linear for low values).

 If we go with a linear Y of 0.0722, these pure saturated colors are all the same luminance:

(0, 0, 1.0)
(0, 0.1, 0)
(0.34, 0, 0)

In 8bit RGB after gamma these would be equal Y RGB:

(77, 77, 77)
(0, 0, 255)
(0, 90, 0)
(156, 0, 0)

This is an image with those colors:

Note the blue and red probably look brighter to you even through they "should" be the same luminance.   The green is about the same brightness as the grey for me on my computer.   There are many places in calibration and cross-computer image viewing that would explain some of why these are not all the same subjective brightness.   But a contributing effect is almost certainly the Helmholtz-Kohlrausch effect, where saturated colors appear brighter than neutral colors.   It's good to be aware of this because it can make you think your math is wrong when in fact your perceptual system is just complicated!

Tuesday, August 18, 2015

SIGGRAPH 2015 proceedings free this week

Via an interesting post from Eric Haines with some cool tidbits.   The whole siggraph 2015 proceedings is free this week

Also Eric notes: Folklore 1: Jim Blinn confirmed that the teapot model was shrunk down because it looked nicer that way, not that the pixels were non-square (incorrectly propagated here and here). Jim & 3D printed teapot.    (I have also spread that false info!   We will know computer graphics has gone mainstream when this is at snopes).