3ac7bb69
From: nospam@null.void
On Wed, 23 Feb 2011 08:00:46 -0800, jogging wrote:
> On 23 fév, 03:34, Glen Walpert wrote:
>> On Tue, 22 Feb 2011 08:15:40 -0800, jogging wrote:
>> > Hi, all
>> > Today I try to find why the captured image is not clear.
>> > I happened to find that blue channel is noisier when I open the image
>> > using photoshop and look at each channel. This is true for most of
>> > about twenty images in my computer. Why? the sensor or optical
>> > system?
>>
>> > Best Regards
>> > Jogging
>>
>> Are these images JPEG compressed? JPEG compression is lossy and throws
>> away information based on visibility to the human eye. The human eye
>> has far fewer short wavelength (roughly blue) cones than medium and
>> long wavelength cones (even more roughly green and red). The eye may
>> have evolved this way because neither predators nor prey are blue, also
>> resulting in an eye where blue is significantly defocused when red and
>> green are in focus, thus higher levels of compression can be used for
>> blue without being evident to the observer.
>
>
> Thanks, Glen.
> But JPEG compression works on the image in YUV color space. so I don't
> think it is related to compression.
>
> I don't understand the statement,
> "blue is significantly defocused when red and green are in focus". Does
> it mean different wavelength need different focus length to be in focus?
> White light is composed of different colors, so it results in being out
> of focus. Does it affect how we sense the objects when we look at them?
>
> Best Regards
> Jogging
Brian already answered the question about blue defocus in the human eye,
but if you want more detail read Foundations of Vision by Wandell. The
first half of the book characterizes human vision in considerable detail
and the second half discusses application of that data to image
compression.
Glen
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