Black level value 在多少以下算比较好的？

lcfyj · 发表于 2007-1-10 09:41:29

我用的OV9660的sensor，不知道black level value 在多少以下才是可以接受的，
请大侠们帮忙！

3homer · 发表于 2007-1-10 12:07:09

请教LZ,所谓"black level value"是指啥啊?

chengsean · 发表于 2007-1-10 13:01:56

Black level value means when you take the picture under DNP and set the exposure time
and gain to minimum. The sensitive(pixel value) should be 0 in ideal condition. But this can't be achieved. So you will see the pixel value is begger than 0 and this value is called black level value.

chengsean · 发表于 2007-1-10 13:13:12

It is hard to say which value is the batter. In general, backend ICs or ISP will have black level compensate. If your ISP or backend ICs do'nt have this function,
the black should be less than 10. If your black level is bigger than 10, after digital gain, CC,
gamma, the value will be enlarge veyr much. So you will see the flare effect in your image.

3homer · 发表于 2007-1-10 14:24:01

和暗电流是什么关系??

lcfyj · 发表于 2007-1-10 14:42:05

纯正的黑的值应该是0，因为有了暗电流所以它的值就不再是零，为了使别的颜色都有统一的计算标准，所以会象线路有GND一样，关学中也就有了一个标准的黑色.

我测的值是12，但是我评价的是RAW data format picture，不知道是不是太大呢？
通过什么方式可以把它降低呢？

3homer · 发表于 2007-1-10 15:42:17

to chengsean

所谓"DNP"是...,,??

chengsean · 发表于 2007-1-10 16:25:23

DNP is as the following figure

The value 12 is good or not. Which pixel depth is your raw data format ?
If your pixel depth is 10bit, the 12 is acceptable. But if your pixel depth is 8bit, this value is
not acceptable.

In general, all sensor will have black level compensate (OBC) function in it.
Some OV spec will have the register setting in the datasheet. But some are not such as OV3630.
If you use sensor OBC fucntion to decrease the optical black level, it is also bigger than
1. The thing you can do is use backend ICs or ISP to decrease it. [br]<p align=right><font color=red>+3 RD币</font></p>

lcfyj · 发表于 2007-1-10 16:51:17

我用的是8bit.

这么经楼上讲解，思路清晰多了，如果有更多相关资料，恳请attach上.

一个DNP要多少钱？有没有好的便宜的供应商可介绍呢？现在我们这边没有 DNP,做Lens shading很麻烦，效果也不好，但是设备比较贵，申请起费用来很麻烦的.

chengsean · 发表于 2007-1-10 18:16:45

DNP is very expensive. As I know, a DNP is higher than 800K $NT. But if your budget is not
acceptable, you can use this one.

I have try this one before, the effect is also acceptable. BTW, I don't know what related
document do you want. Because this is a big issue about adjust good parameter for senosr.
Could you give more detail information about what you want ?

lcfyj · 发表于 2007-1-11 10:42:01

BTW我以前没有听说过，和DNP一样吗？什么样子？大概多少钱？能告诉我相关的供应商的网址吗？

能否发一些black level 改善方法的详细资料呢？

chengsean · 发表于 2007-1-11 17:27:38

http://www.kphoto.com.tw/front/bin/ptlist.phtml?Category=59333

This equipment is used for photographer before. You can buy it in any photograph store.
The black level information, I only have book about sensor and CCD.

tonyhongbin · 发表于 2007-1-29 21:42:58

Hi,chengsean
可以给我们一些sensor中ISP的算法相关的资料吗？

wishercjf · 发表于 2007-1-30 08:39:19

楼主测的12应该就已经不错了.如果在小的话,整个图象看起来就比较暗了.效果不好了.
使用rgb raw的格式的话,dsp需要调试的东西比较多

chengsean · 发表于 2007-1-30 12:43:14

His value is 12 in 8-bit pixel depth and is from raw data.
Let's simulate the 12 value to pass ISP and see the output.

Assume that
1. AWB gain is about 1.5x
2. CC gain is about 1.5x

Then what happen to this value 12.
12 * 4 * 1.5 * 1.5 / 4 = 27.
The darkest value is 27. Your picture will serious flare.

jimi · 发表于 2007-1-31 09:18:14

to chengsean

你的算法值得商榷, 个人认为这个值主要受gamma变换的影响.

((12/255)^0.45)*255=65

CC 一般要求行系数相加应为1.因此对亮度的影响较小.

chengsean · 发表于 2007-1-31 15:17:59

Ya.. Your are right. I neglected the gamma.

lcfyj · 发表于 2007-1-31 17:28:53

前一段时间突然上不了这个网站了，今天上来看到这个主题还在前面很是高兴。谢谢大家捧场.

大家有没有用Qualcomm 的软件Chromatix & QCLIMB 的？

我现在遇到很多问题，但是Quanlcomm 那边的feedback很慢，很多问题都没有回答，
希望有技术高深的大侠给予指点.

另外我又重拍了一下black level,算出的值是8，这样的话是不是效果会好一些呢？

jimi · 发表于 2007-1-31 17:54:29

to chengsean

在那个动态范围的帖子你的见解很精辟,佩服!

tonyhongbin · 发表于 2007-1-29 21:42:58

Hi,chengsean
可以给我们一些sensor中ISP的算法相关的资料吗？

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[讨论] Black level value 在多少以下算比较好的？