タスクジャグラー
I have had similar experience with ProjectLibre and GanttProject and I finally love タスクジャグラー and have never planned projects so fast once I got used to it.
Unfortunately the installation is not so simple, because it needs Ruby, RubyGems and a few gems in order to work, so I wrote the タスクジャグラー Installer for Windows, which does the installation for you (and a few nice things in addition). Disclaimer (if that was not clear enough): I'm the author of the installer.
あなたの要件
タスクジャグラー is based on a text file, so you need to learn some syntax, which may take a few hours. But if you keep things simple, there should not be too high hurdles. Here's a short walkthrough of the things you need according your description:
Define a task by start date and end date:
task t1 "Task 1" {
start 2015-11-06
end 2015-11-16
}
Define a second task as consecutive task and a duration (in calendar days here):
task t2 "Task 2" {
depends !t1
duration 5d
}
Quality of exported image:
Actually, タスクジャグラー does not create an image, it creates HTML. But that's a huge benefit: any browser can zoom today, so you can create an image of the quality you like.
Report only the start and end date:
Honestly, I'm not sure I understood the requirement correctly: do you want only the start and end date of the project (i.e. start of first task and end of last task) or of each single task?
タスクジャグラー by default reports the start and end date of each task (see also the screenshot below). You can create a parent task which then inherits the earliest start date and the latest end date. It would be defined like this:
task taskid "Parent task"{
task t1 "Task 1" {
start 2015-11-06
end 2015-11-16
}
task t2 "Task 2" {
depends !t1
duration 5d
}
}
出力例
Here's the output which is generated by above input (plus some other text required to make it work, see フルコード below). The output of タスクジャグラー is highly customizable. However, doing customization of the output is probably one of the hardest things to do in タスクジャグラー.
(画像をクリックすると拡大します)

フルコード
タスクジャグラー can start with a minimum project. This フルコード example also introduces you to a few other features like a team, comments and different sorts of reports, so you get a more complete picture of the tool.
project projectid "Software recommendations" 2015-11-06 +12m {
timezone "Europe/Berlin"
currency "EUR"
timeformat "%Y-%m-%d"
numberformat "-" "" "," "." 1
currencyformat "(" ")" "," "." 0
}
# This is a comment
/*
This is a multiline comment
*/
rate 300.0
leaves holiday "Christmas" 2015-12-25 +1d
resource teamid "My Team" {
limits {dailymax 6.4h} #80%
resource personid "My Employee" {
leaves annual 2015-01-01 - 2015-01-08
leaves annual 2015-12-23 - 2015-12-31
}
}
task taskid "Parent task"{
task t1 "Task 1" {
start 2015-11-06
end 2015-11-16
}
task t2 "Task 2" {
depends !t1
duration 5d
}
}
resourcereport "resources" {
formats html
columns name, annualleave, annualleavebalance, sickleave, specialleave, unpaidleave
}
macro TaskTip [
tooltip istask() -8<-
'''Start: ''' <-query attribute='start'->
'''End: ''' <-query attribute='end'->
----
'''Resources:'''
<-query attribute='resources'->
----
'''Precursors: '''
<-query attribute='precursors'->
----
'''Followers: '''
<-query attribute='followers'->
->8-
]
taskreport overview "tasks" {
formats html
columns bsi { title 'WBS' },
name, start, end,
chart { ${TaskTip} }
}