The CIE Lab data comparison between IMAQ Vision and Photoshop

[john_mao@htc.com.tw]

Hello~

I'm programming some color check function via IMAQ Vision 7.0 and I found out some unreasonable value appears from "LV_colorHistogram_v2" in CIE Lab color mode while checking some black area in the image.

I've attached a powerpoint file to compare the CIE Lab data difference between IMAQ Vision and Photoshop.

I got CIE Lab calculation in IMAQ Vision Concepts Manual but lacks for Photoshop, so I don't know how photoshop runs.

But in attached comparison, it seems the a* and b* data from Photoshop is much reasonable.

Doese any body know which one is correct CIE Lab data?

[J.Harv]

john

     I would guess that they are both correct.  Since the CIE l*a*b* values are estimations of human perceptions there are several dozen different ways to caluculate them. Also, there is different RGB schemes to consider.  Since our Vision systems usually involve cameras we use NTSC RGB but there are several dozen RGB models. Each respective program simply uses a different approach.  It sounds like you've already found our calculations in the Vision Concepts Manual.  That manual is a goldmine of information, including how we make those specific calculations.  I would suggest posting at Adobe or calling them to find out how their values are calculated.  Then once you know you can choose which values you want to use. Anyway, let us know if you have questions. Thanks.

Regards,

John H.
Applications Engineer
National Instruments
http://www.ni.com/support

[Clauruvi]

Hello Jhon.M

I will do a research about color in food and basically i was thinking to use Labview  to process my images  with NI IMAQ VISION using a camera  CANON G7 which  have a  special software   http://www.breezesys.com/PSRemote/index.htm   program that allows photographs to be taken with a Canon PowerShot camera and viewed within seconds on a Windows PC.

I will use  this software to  get the photographies and process in Labview , but I'd like  to know if NI IMAQ  could read the CIELAB parameters L*, a*,b*  i need this parameters to make my owns comparation  between IMAQ Vision and Photoshop.

Please let me  know if you can help me because  i'm just a begineer in Labview !

Greetings  from Perú.

Claudia!

[John_Mao]

I've attached a simple NI IMAQ Vision program and hope it helps.