Pixel
Depth Reduction
Assignment2
Ken Noonan
DNet4
This
assignment was designed to make us see how pixel depth and colour palettes
combined with dithering all affect an images quality and size. For this
assignment I used the Palm tree image from the sample images supplied in
Photoshop.
Firstly we
were asked to convert to Indexed mode, 256 colours, no dithering
Size: 62.82k
Quality: 8
Then we
were asked to revert to the RGB image, convert to Indexed mode 200 colours no
dithering
Size: 50.19k
Without Dithering
|
Colour |
Size(K’s) |
Quality |
|
160 |
49.03 |
8 |
|
140 |
46.7 |
7 |
|
120 |
43.6 |
6 |
|
100 |
39.8 |
6 |
|
80 |
36.12 |
5 |
|
60 |
31.14 |
4 |
|
40 |
26.68 |
3 |
|
20 |
18.13 |
2 |
|
10 |
12.6 |
1 |
|
8 |
11.23 |
0 |
The quality
of the image with no dithering remained quite good throughout. The colour
starts to give around the 140 mark. And this was only very noticeable when you
zoomed in on the image. As is shown from the above table the size reduces with
the colour and hence the quality. It becomes unacceptable at 30.
We were
then asked to revert to RGB, convert to Indexed mode
256 colours, with dithering to adaptive palette.
Size: 62.82K
Quality: 10
Convert to
240 colours, with dithering to adaptive palette
Size: 61.98k
Quality: 10
With Dithering(100%)
|
Colour |
Size(Ks) |
Quality |
|
220 |
61.85 |
10 |
|
200 |
60.67 |
10 |
|
180 |
58.89 |
10 |
|
160 |
57.46 |
9 |
|
140 |
55.5 |
8 |
|
120 |
52.13 |
7 |
|
100 |
49.68 |
7 |
|
80 |
45.68 |
6 |
|
60 |
41.77 |
6 |
|
40 |
37.66 |
5 |
|
20 |
29.42 |
3 |
|
10 |
21.35 |
2 |
|
8 |
19.43 |
2 |
The image,
with dithering, starts to give around 130. This is only very slightly
noticeable in the sky. At 15 the image is unacceptable. In my opinion the best
value is when the colour palette is at 60. The quality here is still very
acceptable and the size is 41.77k.
If you
compare the two tables above you can see clearly where the quality and size can
be compromised. For example if you use 120 colour palette with no dithering you
get a 43.6K sized image with image quality at 6, whereas you can get the same
quality image with 100% dithering
and an 80 colour palette with image size 45.68k.
Dithering
results in a larger file size but with a smaller colour palette.