COMP6023 DCOM1b Classes 27 & 28

We did some experiments with dithering in Photoshop.

COMP6023 ITM1 Classes 27 & 28 Lab

We did some experiments with dithering in Photoshop.

COMP6021/COMP6023 Animated GIFs Documentary

COMP6021/COMP6023 JPEG

Here's an online video I made some time about about JPEG. It is largely the same as what we did in class.

This rather unusual logo has it origins in the way JPEG works.

COMP6023 DNET1 Labs

For the remaining 6 weeks of the semester the DNET1 labs will be taken with James O'Sullivan. I will still see students in the lectures.

COMP6023 DNET1/COM1c Class 26 GIF & JPEG

We looked at GIF & JPEG image formats.

[no recording due to technical problems]

COMP6021 Class 25 GIF & JPEG

the one with the DCT

We looked at the main features of the GIF and JPEG image formats.

COMP6023 DWEB1/ITM1 Class 26 GIF & JPEG

We looked at the main features of GIF & JPEG.

Students now ave everything they need to complete Assignment 2.

COMP6023 DWEB1/ITM1 Class 25 Indexed Colour and Dithering

We looked at indexed colour, colour palettes, and dithering.

COMP6023 Essay title errors and omissions

Today I corrected any errors in the essay choices of which I was made aware.

Students may no longer chose a topic. That choice was made for them some time ago.

However, if you made a choice, advised me of it, and the list does not reflect that please let me know and I will try to find the e-mail you sent me.

Please check the list to ensure that the blog URL and essay title are correct.

COMP6023 DCOM1 Class 25 Subsampling, Indexed Colour & Dithering

[no recording today]

We looked at subsampling and interpolation. We saw how 24 bit images can be coded with fewer bits per pixel by using a well chosen palette. We played a palette matching game.

I explained how dithering works and students did an exercise on dithering. There are more such exercises in the notes, for students interested in doing more.

COMP6021 Online Class: Dithering

COMP6023 DNET1/COM1c Class 25 Dithering

We looked at dithering. [no recording]

We did an exercise in class. There are other similar exercises in the slides.

I answered a few questions about interpolation.

COMP6023 DCOM1 Class 24

We looked at the Lab and CMYK colour systems.

We finished a bit earlier than usual. I wasn't keeping an eye on the time. It felt longer. I guess I was tired :-)

COMP6021 Class 24

the one with Colin's tie

We looked at indexed colour palettes and at dithering.

Only 5 students were in class.

COMP6021 Online Class: 1-bit images

COMP6021 Compression

COMP6023 DWEB1 Class 23 & 24

Students worked on their blogs and on assignment 2.

COMP6021 Class 23 Lab

We looked at an images RGB, CMYK, and Lab channels using Photoshop.

Students converted images from RGB, to Lab and then subsampled the a and b components so that they were a mere 1/36th of their original sizes. The results were surprising good in most cases.


In these images 35/36ths of the colour information has been discarded. Look closely to see the impact of this.

Original PNG.

Subsampled Colour.

If you were on holidays and paying roaming fees to upload the picture you would would pay 3.00 for the full quality picture, but only 1.05 for the low quality.

COMP6021 Class 22

We looked at the Lab system and the CMYK system. The Lab system was interesting because it separates out the luminance and chrominance components of a image. We say how subsampling the chrominance components of an image can be quite successful.

We considered the use of subsampling as crude compression mechanism and looked at interpolation to replace the lost data.  in practice, interpolation is more complex that I explained.