Can cheap HDMI cables really give a poorer image?

Yes, it is possible for a cheap HDMI cable to produce a poor image, as you are seeing.

Effectively, your cable is "dodgy", and is distorting the "digital" signal so much that it is corrupting the bits on the way through. This is much like a "marginal" signal for digital TV - you still get a picture, but it freezes and is quite blocky because parts of the digital stream are missing and the decoder is trying to cope with it

In your case, I wonder if just one of the connections on your cable is not connected. I had a similar problem with a DVI-HDMI cable, which gave me a signal, but a lot of static/lines unless I wiggled the cable and got it just right.

The meme that there is no difference between a cheap expensive digital cable is fairly accurate, but not 100%. If the cable can get all the bits across it without corruption, the result of the cables is identical.

HDMI is a standard- so any cables which conform to this standard should work fine.

The only way a cheap HDMI cable is going to cause problems is if it's sub standard- but I've never come across one that bad before.

I've found no difference between $7 HDMI cables from eBay, and $70 brand cables with gold-plated connectors.

Due to the nature of the digital signal- the picture either tends to either be "perfect", or suffer from obvious macroblocking or have very obvious interferences lines through it. Differences are not subtle- and if you're having to look closely to notice a difference, you're probably not noticing problems caused by your cheap HDMI cable.

I've even connected 3 "cheap" HDMI leads end to end to connect a laptop to a TV the other side of a living room, and it works as well as when a short run of expensive HDMI cable is used.

So, in other words: don't get sucked in by the marketing guys who try to make you feel you need to pay a lot for good quality.

"Cheap" isn't really an indicator of anything. As Austin ''Danger'' Powers explained, there's a standard, well actually a series of standards, and to legally bear the HDMI logo, the cable has to comply with one of the standards. It's possible that some shady manufacturers are selling cheap cables by saving manufacturing costs and making non-compliant cables. That would be more a question of a misleading sales practice through false use of the HDMI logo on the product. Causing signal loss by wiggling the plug on a new cable, when similar action doesn't affect other cables, would suggest some shoddy manufacturing, though.

Aside from the loose plug issue, the problem is more likely the use of an HDMI cable that meets a standard too low for the application. At the current time, there have been something like nine versions of the HDMI spec, with successive versions sometimes requiring a more sophisticated cable to support the signals. mr.spuratic's answer mentions "Standard" and "High Speed cables". Since that time "Premium" and "Ultra High Speed" have been added to the list (and there are actually some other categories for other cable uses).

Those cable categories define construction that supports the requirements for different levels (versions) of the HDMI standard. The HDMI standard has evolved to support more and more demanding applications. If the original cable design was adequate for the requirements of the later standards, there would have been no need for the later cable designs. Those cable categories aren't marketing terms to sell fancier-looking cables with useless features at higher prices, they are actually different designs needed to support the demands of the usage made possible by the later spec.

Manufacturers are still free to sell cables that meet only early versions of the HDMI spec (Standard cable), and there are still applications for which those cables are fine. But if you have a more demanding requirement, you will get the kinds of crappy performance described in this thread if you don't use a cable designed to support it. In terms of "cheap cable", each successive "level" of cable is going to be more expensive to manufacture (and will have a price marked up to what the market will bear), so a Standard cable will be "cheap" compared to a High Speed or Premium cable.

Some of the capabilities of the successive HDMI specs are summarized in these tables (courtesy of Wikipedia):

Standard Video (refers to the video, not the cable):

Feature Support:

The Wikipedia article summarizes the cables that support the different levels of requirements. The general use ones:

• Standard HDMI Cable – up to 1080i and 720p
• High Speed HDMI Cable – 1080p, 4K 30 Hz, 3D and deep color
• Premium High Speed HDMI Cable - 18 Gbit/s HDMI 2.0 bandwidth
• Ultra High Speed HDMI Cable (48G Cable) – 4K, 5K, 8K and 10K at 120 Hz (48 Gbit/s HDMI 2.1 bandwidth)

HDMI's website describes them in a little more detail. I'll excerpt the general use cables:

Standard HDMI Cable
The Standard HDMI cable is designed to handle most home applications, and is tested to reliably transmit 1080i or 720p video – the HD resolutions that are commonly associated with cable and satellite television, digital broadcast HD, and upscaling DVD players.

High Speed HDMI Cable
The High Speed HDMI cable is designed and tested to handle video resolutions of 1080p and beyond, including advanced display technologies such as 4K, 3D, and Deep Color. If you are using any of these technologies, or if you are connecting your 1080p display to a 1080p content source, such as a Blu-ray Disc player, this is the recommended cable.

Premium High Speed HDMI Cable and Premium High Speed HDMI Cable with Ethernet
are special certification designations for High Speed HDMI Cables that have been designed and certified for ultra-reliable performance for 4K/UltraHD including advanced features such as 4K60, HDR, expanded color spaces including BT.2020, and 4:4:4 chroma sampling. They have low EMI and are identified by HDMI Licensing Administrator’s Premium HDMI Cable Certification Label for authentication verification.

Ultra High Speed HDMI Cable
ensures ultra high-bandwidth dependent features are delivered including uncompressed 8K video with HDR. It supports up to 48Gbps bandwidth and features exceptionally low EMI (electro-magnetic interference) which reduces interference with nearby wireless devices. The cable also supports the HDMI Ethernet channel. It is backwards compatible and can be used with the existing installed base of HDMI devices.