Canon 60D moire & aliasing issue on videos

Question

Is it a common issue on canon 60d to have moire & aliasing issue when recording videos. Or is it that my sensor or lens has a defect? I'm using the kit lens EF-S 18-135mm IS.

Does anyone here have this issue?

Turning down sharpenss & contrast didn't help.

Asked by Petrick Lim

Answer

Aliasing (and therefore moire, a type of aliasing) is a problem for almost all Canon DLSRs (as well as other manufacturers). The root cause is line skipping, whereby in order to get the necessary framerate only every third line of pixels is read from the chip.

If you have fine detail that is about the same size as a line of pixels then as the camera moves the detail will pop in and out of existence as it passes each active line of pixels.

The latest generation of sensors to be found in the 1DX and 5D mkIII apparently address this issue by reading the whole sensor and downsampling in order to produce the 1080p image.

The issue can be remedied to an extend by mounting an anti-aliasing filter (much stronger than the one in front of the sensor) on the lens. This blurs the image so that the detail will be spread over several lines, and not pop in and out as it crosses an active line of pixels.

Answered by Matt Grum

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Can I get high resolution photo from video?

Question

Waiting for the exact moment to snap a picture can be very difficult especially when working with children or animals. I've read somewhere (can't find source) that every freeze frame from an HD video is essentially a high-resolution photo (is this even true?).

What are the challenges, pros, and cons of selecting the best frame from a video as a way of taking still photos where timing is crucial?

Answer

The big pro to this is, as you say, the ability to take many pictures in a short period of time, allowing you to pick the best frame.

However, there are several cons to this approach:

• Lower resolution. Even "Full High Def", 1080p, is only 2 megapixel (1920 * 1080 = 2,073,600). This would give you an acceptable print size of 6.4x3.6 inches, at 300 DPI. This might be fine for you, but if you want a larger print, you'll start noticing pixellation.
• Often, less control of settings like shutter speed, ISO, and aperture. Video also can generally deal with a bit more motion blur than still photos, and the camera may allow the shutter speed to drag longer than you might want.
• Video compression artifacts. Aside from key frames, most frames in a compressed video are rendered by modifying a prior frame. This results in artifacts that may not be noticeable in a video, but will degrade the quality of your photo. This depends a lot on the codec and the bitrate of the video.

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So why does Canon 5D Mark II have a better video quality than Canon 60D?

Question

Assuming that Canon 5D Mark II and Canon 60D both have the same processor, DIGIC 4 (single), why does the former shoots a better quality video? Better quality I mean the technical aspect, the video/compression itself.

Let's ignore the visual aspect like more shallow depth of field, for example.

I know 5D is a full-frame, but the video is 1920px wide. The 60D shoots 18MPx, which scaled down to 1920px wide should still look almost the same as if shot on full-frame initially, right?

Therefore, and this is my point:

UNCOMPRESSED INPUT -> DIGIC 4 -> OUTPUTTED VIDEO

If we exclude the depth of field and a better ISO handling from our equation, it's possible that the uncompressed input is the same on both cameras, right? Then, it goes to the digic 4 processor to be compressed, which is the same on both cameras. Yet, we end up with a better quality video on one of those cammeras. Why?

Answer

The 5D Mk2 has a far larger sensor (because its a full frame camera) and more pixels. My assumption would be the camera scales down the input to 1920x1080 so having more uncompressed data allows it to give a higher quality output.

If Andres's comment about it skipping lines whilst taking video is right, then the improvement in quality is more likely down solely to it's lower pixel density. A lower pixel density means a bigger area per pixel, which means more light per pixel, more light per pixel means less amplification is required (amplification increases noise also)

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Does this calculation for Canon 60D vs. Canon 7D video recording work?

Question

The latest official manual for Canon 60D says that a 1920x1080 movie with any FPS recorded takes up 330 MB/min.

The latest official manual for Canon 7D says that a recording with the same movie settings on this camera will also take up 330 MB/min.

Does this definitely mean both the cameras produce exactly the same results, or may it still be possible that one of the cameras produces worse video recording?

I'm sure it could be possible if those cameras were totally different, using different codecs for encoding, etc, but as those cameras are very similar and definitely using the same compression, I assume the aforementioned could be true, which makes me to ask the ultimate question: is the double DIGIC4 processor in Canon 7D useless when using it for shooting a video, compared to a single DIGIC4 processor in Canon 60D?

Answer

As you said, they could be 100% identical.

In all likelyhood they are not but given the bit-rate is the same for the same resolution, frame-rate and codec, I think it is safe to say that any difference will probably be negligible.

You are probably right that the second processor is probably not fully needed for video in this case. It is probably there to improve full-resolution continuous shooting.

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