Megapixels and resolution: K-x 12MP beats 18MP Canon 60D. Why?

rawr · 10-06-2010, 03:31 PM

[This is not really a camera specific issue, so I thought I'd post this here, rather than in DSLR Discussion].

I've long been puzzled by this. Maybe someone can explain why this is so.

I know in theory a 12MP camera (like the K-x) should deliver less resolution than a 18MP camera (like Canon's 550D/60D/7D or similar). But in charts like the ones below this isn't the case, and it is a consistent issue.

A 12MP camera like the K-x can even be shown to deliver consistently HIGHER resolution than the 60D. For example in the charts below one can see that from ALL ISO's above ISO 400 the resolution of the K-x exceeds that achieved by the 60D (at the RAW centre). Only in the JPG measurements does the 18MP camera consistently beat the 12MP camera, but even in JPEG the resolution difference is sometimes only marginal.

K-x chart sourced from Photoreview.com.au camera review for the K-x

60D chart sourced from Photoreview.com.au camera review for the Canon 60D.

You can also see similar results to the 60D from the Photoreview Canon 7D camera review.

This isn't just a measurement issue with Photoreview.com.au. DPreview notes the same in their 550D review: "The difference between the raw output of the EOS 550D and the Pentax K-x is ... so subtle as to be almost irrelevant to normal photography at print sizes smaller than A3."

Only when you move into Canon 5D2 (22MP) or Nikon D3x (24MP) territory do you see consistent high resolution being achieved in the Photoreview.com.au test charts.

This issue of interest to me. I've recently been doing a lot of birding and being able to crop heavily into shots has always been one of the attractions in the back of my mind about (affordable) higher megapixel cameras like the 550D and 60D, not to mention new cameras like the K-5.

But according to what I am seeing in these charts and tests, if I stick to RAW and use a good RAW processor (eg LR3) - which is what I am doing now - I won't gain any practical, usable resolution improvement from moving from the K-x up to a higher resolution camera like the 60D or K-5.

Not until I move into big money camera territory like the D3x (which is not going to happen) will I see a real RAW resolution advantage (ie > than 25%) above the K-x.

tl; dr: Why doesn't 18MP deliver SIGNIFICANTLY more resolution than 12MP?

Last edited by rawr; 10-06-2010 at 03:37 PM.

elho_cid · 10-06-2010, 03:53 PM

I have the same impression, My friend purchased a 550D earlier this year and I had the opportunity to insert my SD card and shoot few images. I was not impressed with the picture quality, even though he had a great 200/2.8L lens on it. I didn't notice much resolition difference compared to my K10D with Sigma 180/3.5.
I believe there are 3 reasons to it:
1) while there is 25% more pixels to each side, the sensor itself is in fact physically smaller. More resolution is lost to physics.
2) Stronger filter in fron of the sensor - Pentax is known for having the AA filter very light.
3) Noise reduction - Canon CMOS sensors have integrated noise reduction that makes the images appear softer.

But I do not expect much advantge form the K-5 as well and yet I ordered one. For me this resolution is good enough. If it wouldn't then 5D mk2 is the way forward.

rawr · 10-06-2010, 05:11 PM

I think there are indeed probably several explanations for the rather puzzling relationship between megapixels and resolution evident here. I must read up more on the subject of digital camera resolution.

I am guessing that whatever is going on is why Nikon was comfortable sticking with 12MP (D300, D5000, D90, D300s, D700 etc) for so long.

brofkand · 10-06-2010, 06:57 PM

Resolutions is much more than just how many pixels vertically times how many pixels horizontally.

What this means is either there is noise reduction going on that blurs detail, decreasing "detail" resolution, or flare from the lens, reducing "contrast" resolution, etc.

It's one of the reasons a 35mm exposure on ISO 50 film has higher resolution than ISO 400 film; they are the same size but if you enlarge both up to say 11x14 or larger, the ISO 50 shot will still be reasonably sharp, have decent to low grain, and still good contrast. The inverse is true of the ISO 400 film.

shadmanaj · 10-08-2010, 09:01 AM

Yay for the K-x!! Thanks for clearing up about resolution.
AJ

10-06-2010, 03:31 PM	#1
rawr Veteran Member Join Date: Jun 2009 Posts: 11,913	Megapixels and resolution: K-x 12MP beats 18MP Canon 60D. Why? [This is not really a camera specific issue, so I thought I'd post this here, rather than in DSLR Discussion]. I've long been puzzled by this. Maybe someone can explain why this is so. I know in theory a 12MP camera (like the K-x) should deliver less resolution than a 18MP camera (like Canon's 550D/60D/7D or similar). But in charts like the ones below this isn't the case, and it is a consistent issue. A 12MP camera like the K-x can even be shown to deliver consistently HIGHER resolution than the 60D. For example in the charts below one can see that from ALL ISO's above ISO 400 the resolution of the K-x exceeds that achieved by the 60D (at the RAW centre). Only in the JPG measurements does the 18MP camera consistently beat the 12MP camera, but even in JPEG the resolution difference is sometimes only marginal. K-x chart sourced from Photoreview.com.au camera review for the K-x 60D chart sourced from Photoreview.com.au camera review for the Canon 60D. You can also see similar results to the 60D from the Photoreview Canon 7D camera review. This isn't just a measurement issue with Photoreview.com.au. DPreview notes the same in their 550D review: "The difference between the raw output of the EOS 550D and the Pentax K-x is ... so subtle as to be almost irrelevant to normal photography at print sizes smaller than A3." Only when you move into Canon 5D2 (22MP) or Nikon D3x (24MP) territory do you see consistent high resolution being achieved in the Photoreview.com.au test charts. This issue of interest to me. I've recently been doing a lot of birding and being able to crop heavily into shots has always been one of the attractions in the back of my mind about (affordable) higher megapixel cameras like the 550D and 60D, not to mention new cameras like the K-5. But according to what I am seeing in these charts and tests, if I stick to RAW and use a good RAW processor (eg LR3) - which is what I am doing now - I won't gain any practical, usable resolution improvement from moving from the K-x up to a higher resolution camera like the 60D or K-5. Not until I move into big money camera territory like the D3x (which is not going to happen) will I see a real RAW resolution advantage (ie > than 25%) above the K-x. tl; dr: Why doesn't 18MP deliver SIGNIFICANTLY more resolution than 12MP? Last edited by rawr; 10-06-2010 at 03:37 PM.

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10-06-2010, 03:53 PM	#2
elho_cid Veteran Member Join Date: Dec 2007 Location: Prague Photos: Gallery Posts: 1,199	I have the same impression, My friend purchased a 550D earlier this year and I had the opportunity to insert my SD card and shoot few images. I was not impressed with the picture quality, even though he had a great 200/2.8L lens on it. I didn't notice much resolition difference compared to my K10D with Sigma 180/3.5. I believe there are 3 reasons to it: 1) while there is 25% more pixels to each side, the sensor itself is in fact physically smaller. More resolution is lost to physics. 2) Stronger filter in fron of the sensor - Pentax is known for having the AA filter very light. 3) Noise reduction - Canon CMOS sensors have integrated noise reduction that makes the images appear softer. But I do not expect much advantge form the K-5 as well and yet I ordered one. For me this resolution is good enough. If it wouldn't then 5D mk2 is the way forward.

10-06-2010, 05:11 PM	#3
rawr Veteran Member Join Date: Jun 2009 Posts: 11,913 Original Poster	I think there are indeed probably several explanations for the rather puzzling relationship between megapixels and resolution evident here. I must read up more on the subject of digital camera resolution. I am guessing that whatever is going on is why Nikon was comfortable sticking with 12MP (D300, D5000, D90, D300s, D700 etc) for so long.

10-06-2010, 06:57 PM	#4
brofkand Pentaxian Join Date: May 2009 Location: North Carolina Posts: 836	Resolutions is much more than just how many pixels vertically times how many pixels horizontally. What this means is either there is noise reduction going on that blurs detail, decreasing "detail" resolution, or flare from the lens, reducing "contrast" resolution, etc. It's one of the reasons a 35mm exposure on ISO 50 film has higher resolution than ISO 400 film; they are the same size but if you enlarge both up to say 11x14 or larger, the ISO 50 shot will still be reasonably sharp, have decent to low grain, and still good contrast. The inverse is true of the ISO 400 film.

10-08-2010, 09:01 AM	#5
shadmanaj Forum Member Join Date: Aug 2010 Location: NYC Posts: 82	Yay for the K-x!! Thanks for clearing up about resolution. AJ