# [argyllcms] Re: [Possible bug in Spyd2.c] Inconsistant readings from Spyder3

• From: Graeme Gill <graeme@xxxxxxxxxxxxx>
• To: argyllcms@xxxxxxxxxxxxx
• Date: Sat, 07 Mar 2009 02:50:32 +1100

```howdy555@xxxxxxxxx wrote:
```
```The spyder 3 produces values of exactly 0.0 all the time for black on my CRT.
```
```So even if there is a problem of erroneous readings of something close
to zero, it would be indistinguishable from valid measurement...
```
```
I figure it's showing this problem all the time on my
display, because the brightness is below the quantization
threshold, even with an integration count of 32e6.

```
```Could I ask you to try to measure very dark grey (I tried using XYZ: 0.196480
0.200497 0.384248) instead. Maybe you would be able to reproduce the problem.
Please make at least 20 measurements before giving up :)
```
```
If I choose and R=G=B on my display to give a Y of about 0.2, this is what
I get:

Reading X   Y   Z
1   0.000000    0.175008    0.124630
2   0.000000    0.176625    0.126857
3   0.000000    0.177723    0.127206
4   0.106032    0.187275    0.159078
5   0.106109    0.187766    0.162659
6   0.000000    0.122717    0.193857
7   0.000000    0.180656    0.130376
8   0.107101    0.190537    0.163706
9   0.000000    0.182667    0.132824
10  0.109261    0.191781    0.165216
11  0.156973    0.134002    0.232604
12  0.000000    0.182397    0.132627
13  0.109114    0.191958    0.165993
14  0.109026    0.191553    0.165962
15  0.158718    0.134652    0.232149

so the X value seems to be quantized below about 0.1.
Given that typical LCDs have a white of about 400, this is
0.025%, not unreasonable in many ways. Measuring my
CRT it's not so good, since it's brightness is about 50
(i.e. this then amounts to 0.2% for my CRT).

```
```Also, could you make the same test but with full white and about 20
measurements? Does the result decrease, increase or stays more or less
the same?
```
```
It depends on the stability of the display of course. Many LCD
displays drift markedly on warmup, sometimes for extended
periods of time (20 minutes ?) - I know my MacBook display does.

On my CRT it bounces around a bit (possibly because the Spyder 3
doesn't seem to have the same smarts as the Spyder 2 to synchronize
it's readings to the refresh rate), but there were no obvious
trends.

```
```[For comparison the i1pro produces XYZ values of 0.048 0.051 0.064,
and the Spyder 2 values of 0.035 0.042 0.043 ]
```
```So the error is 0.064 -> perfectly acceptable for me :) I was
referring to errors of about 0.200 when measuring a value of about
0.200 :).
```
```
Right, but what's your white level ?

It's interesting that the specifications for the Spyder 3 seem to
be less comprehensive than the Spyder 2.

Spyder 3:

Accuracy (x,y typical)        0.0025

Spyder 2:

Accuracy: Chroma x,y:         0.0020 (CRT), 0.0035 (LCD)
Luminance:                    Y Typical +/- 1.5%
Dynamic Range:                Black Point: 0.02 cd/m2,
White Point:                  > 5,000 cd/m2

Graeme Gill.

```