Image Quality

[sury]

I tried to ask this question in another thread of mine and also on DPR pro-digital talk but did not get any replies. Canon 5D MKII highest resolution JPEG image files are approximately between 5-8 MB as seen on my friend's 5DMKII. Whereas, typical A900 JPEG images are anywhere from 14-21MB. How is that Canon is able to manage image quality with such high compression? I did some samples and I am getting about 1:2 compression between RAW and JPEG images. That explains the size difference but not quality of the image.

My friend's hypothesis is that Sony has conspired with disk/card manufacturers. Just kidding.

With best regards,
Sury

[David Kilpatrick]

Two things - lower noise levels in the image, and more smoothing (noise reduction) leading to loss of fine detail. JPEG size increases with noise, with accuracy of focus and wealth of detail in the subject (textures etc), with sharpness setting (set +3 sharpness and your JPEGs get bigger), and also with the richness of the colour palette (colour discrimination).

The A900 has much better native sharpness and colour rendering, it may also have better lenses (especially if CZ is used, that can increase JPEG size a fair amount), and on the downside it also tends to have more noise (but with this, more detail).

David

[sury]

David,
Thank you for that explanation. If I were to take the discussion further, can I then classify "noise" having two behaviors?
One being a non-desirable (as seen in shadows of an high ISO image) and the other adding texture and details and therefore desirable? If that is the case, I am hard pressed to believe the size difference is 2X to 3X and not some percentage. Since he shoots with 70-210/f2.8 IS L series lens, one of these days I am gong to rent the Sony 70-210/f2.8 and do a comparison shoot session. I am now very curious.

Sury

[David Kilpatrick]

I don't know if noise is desirable really, but noise reduction to the point of losing textural detail is not - for sure. I've used the 5D MkII, and I don't think the images are softer than the A900 in overall contrast or lower in sharpness for clearly define edges. There is something about the image which looks smoother and perhaps a little less realistic. The 70-200mm Canon is one of the best lenses they have.

However, at ISO 100 where neither camera has noise, I've just compared my studio shots (identical) made with the 5D MkII and A900 - both are almost exactly 6.21MB as a JPEG. See:
http://www.photoclubalpha.com/2008/12/1 ... dmkii-d3x/

First two pic examples.

If anything the Canon file is larger in relative terms. Some of the Canon outdoor scenes make JPEGs 10-13MB in size. And although I have thrown away most of my A900 JPEGs and only kept the raws, I have found a few scenes compressed down to 7-8MB.

So I think it's down to the individual shot, the focus accuracy, the noise reduction and ISO speed set - loads of factors. I do not think the Canon files are always smaller than the Sony ones.

David

[sury]

(Stuff deleted)

So I think it's down to the individual shot, the focus accuracy, the noise reduction and ISO speed set - loads of factors. I do not think the Canon files are always smaller than the Sony ones.

David

David,
Only plausible explanation I have now is about individual shots. He has the camera for about 3 weeks now and claimed not a single one exceeded 7MB. I will ask him for some land scape shots. It is likely that he is taking portraits with tight crops even out doors and that is in line with your reasoning. Thank you for taking time to explain and your insight is appreciated as always.

With best regards,
Sury

[destrianlives]

Dude it depends on the image. I've seen brightly lit city scenes for my a700 taken and have jpg imagesabout 3-4mb and others from the same shoot at the same manual settings have 2 mb images.

[gilroy]

Thank you for that explanation. If I were to take the discussion further, can I then classify "noise" having two behaviors?
One being a non-desirable (as seen in shadows of an high ISO image) and the other adding texture and details and therefore desirable? Sury

Yes, you are correct about this. I might actually call this "noise" high freq information. Behavior 1 noise is undesirable as it is random, while the desirable behavior as you mention is the non-random component (details in the textures etc.)
Jpeg compression works in the freq domain - and what this blabber means is that the image signal with high freq components (good and bad noise) when jpeg compressed is going to increase the filesize.
I can't say much about the differences between the cameras and the lenses etc. that contribute to the noise, as I don't know.

Regards,

gilroy

[sury]

Dude it depends on the image. I've seen brightly lit city scenes for my a700 taken and have jpg imagesabout 3-4mb and others from the same shoot at the same manual settings have 2 mb images.

At the cost of repeating myself, I am baffled by the stated file sizes. 5DMKII manual says the typical image size is around 7MB when talking about card capacity. Whereas the typical size of Standard JPEG for A900 is around 6MB (page 33 of the manual, 148images/1GB card). The highest resolution JPEG on A900 per manual is around 20MB (43images/1GB card). Such a variance as described in the manual could not be explained as "it depends on the image". I am aware of the fact that for a given camera different images take up different sizes.
Shouldn't a 21MP camera highest resolution JPEG size not be in the neighborhood of of a A900 (less 12% due to MP difference) highest resolution for the same scene? If so, why it isn't? If not, then why not? That is my question.

With best regards,
Sury

[harvey]

At the cost of repeating myself, I am baffled by the stated file sizes.
Sury

JPEG compression works by taking blocks of the image and turning them into a set of components at different spatial frequencies. Then the compression is done by throwing away the higher frequencies based on what quality you pick and a table of coefficients that varies by manufacturer/camera/software package.

So you can't expect the sizes to be the same.

Harvey

[David Kilpatrick]

Don't forget that Sony offers Extra Fine JPEG (which can not be shot alongside RAW, only on its own) and Canon does not offer this.

Therefore the largest JPEG size from the A900 will be Extra Fine, but Canon only offers Fine. I know a lot of Sony owners don't find much difference between X Fine and Fine, and therefore never use X Fine, but there is a difference clearly as the filesizes show.

I have just done a quick test of a highly detailed (green garden - luminance values predominate) scene on the 50mm at f/8. Fine - 14.2 MB, Extra Fine - 25.3 MB. I do not have a Canon 5D MkII here to compare, but my guess is that the Canon with 50mm prime lens and similar settings would be around 11 MB.

David

[alphaomega]

David Kilpatrick stated above

I have just done a quick test of a highly detailed (green garden - luminance values predominate) scene on the 50mm at f/8. Fine - 14.2 MB, Extra Fine - 25.3 MB.

with the A900 I presume.
I wonder if he would like to share the results. Did he find any difference between fine and X fine when looking at the grass leaves level? I would be interested to know as presumably the same observations might apply to the two Jpeg levels on my A700.

[David Kilpatrick]

The pic is scruffy, no desire to post it - the answer is that althoughthe X Fine must have more detail, I honestly can't see it even at 100 per cent.

What I found with the A700 was that X Fine held together better if you wanted to adjust the JPEG later - levels, sharpening etc. If you left it alone, it was almost impossible to see the artefacts created by the higher compression level, but if you start making extreme adjustments they begin to show up.

If I want to adjust, I shoot raw, so I simply don't use X Fine. When I need JPEG only, it is for casual stuff and I may even set the smallest file size, the last thing I need is a 24 megapixel routine quality JPEG!

David

[agorabasta]

The pic is scruffy, no desire to post it - the answer is that althoughthe X Fine must have more detail, I honestly can't see it even at 100 per cent.

You could resave XFine to Fine in Sony junk software, then open in some editor and subtract one from the other. The result is quite telling.

[sury]

You could resave XFine to Fine in Sony junk software, then open in some editor and subtract one from the other. The result is quite telling.

I did that with a JPEG file. I opened Photoshop 7 and copied original to my low res image and did a blending of difference. Difference gave me a black screen. Is there another method of "subtracting"?

With best regards,
Sury

[agorabasta]

Difference gave me a black screen. Is there another method of "subtracting"?

Check the histo - if there's something in the shadows, then stretch it out.
Should work.