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IRIX 6.2 Applications 1996 August
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Silicon_Graphics_812-0542-002.iso
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imgtools
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ch3.z
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1996-08-03
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3. _C_h_a_n_g_e_s__a_n_d__A_d_d_i_t_i_o_n_s
This chapter lists changes and additions new to release 2.2
of IRIS ImageVision Tools.
3.1 _J_F_I_F__a_n_d__G_I_F__f_i_l_e__s_u_p_p_o_r_t_:__n_e_w__s_u_p_p_o_r_t_e_d__f_i_l_e__f_o_r_m_a_t_s
The ImageVision Tools now support reading and writing the
JPEG compressed file format JFIF, as well as reading and
writing the GIF file format.
3.2 _I_m_a_g_e__V_i_e_w__G_I_F__a_n_d__J_F_I_F__f_i_l_e__s_u_p_p_o_r_t
Image View can now write images using GIF and JFIF (JPEG-
compressed) file formats. To choose GIF or JFIF file
output, choose Save As... and select the desired file
format from the buttons in the file browser.
Image View writes GIF and JFIF images using presets which
are suitable for many uses. For better control over GIF and
JFIF output quality, use Image Works to convert images to
these formats.
3.3 _I_m_a_g_e__W_o_r_k_s__J_F_I_F__f_i_l_e__s_u_p_p_o_r_t
Image Works allows you to choose compression quality when
you write an image to the JFIF file format. To do this,
choose Save As... and select JFIF output from the menu in
the file browser. Then adjust the quality slider to the
desired setting.
To preview the effects of the image quality setting in
advance, use the compview(1) utility.
3.4 _I_m_a_g_e__W_o_r_k_s__G_I_F__f_i_l_e__s_u_p_p_o_r_t
Image Works now allows you to control several options when
you write an image to the GIF file format. These options
help you prepare images for World Wide Web documents or
other means of on-line distribution. To change these
options, choose "Set GIF Options..." from the File menu or
the Save As... file browser.
"Number of Colors to Save" allows you to choose the maximum
number of colors to use in the color palette of the GIF
image. You can choose 16, 64, 128, or 256 colors. By
default, Image Works uses 64 colors.
More colors will give you a better quality image. You may
want to choose many colors to accurately represent
photographs or other highly realistic imagery.
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Fewer colors will help save disk space and network
transmission time. Use this option for diagrams, line
drawings, graphics composed of spot colors, and other simple
graphics.
Finally, if you prepare images for the World Wide Web,
remember that your content is viewable by a worldwide
audience. Internet users will view your images using a wide
range of computer systems and software, with varying color
graphics capabilities. To place fewer demands on the
viewer's web browsing hardware and software, you should
choose the fewest colors to provide acceptable quality for
your images. If you place several images into one page, use
fewer colors in each image to help web browsers faithfully
show all the images.
"Use Dithering" allows you to control how Image Works
reduces the number of colors in an image. Dithering is a
process which changes the pixels in an image to simulate
lost colors. By default, Image Works uses dithering, but for
some types of images (such as screen snapshots, line art,
and simple graphics) you may get better results by
unchecking this option.
"Use Interlacing" allows you to control the way Image Works
arranges image data in a GIF file. Interlaced images allow
World Wide Web browsers to quickly show a rough version of
the full image, then progressively refine visual detail as
they read more image data. By default, Image Works uses
interlacing when writing GIF images. You can uncheck this
option if you want smaller GIF files that do not allow
progressive display.
"Choose Transparency Color" allows you to make a solid color
of your image transparent. This allows you to create Web
images with nonrectangular graphics.
To choose the transparency color, click the "Choose
Transparency Color" button, move the pointer over the pixel
in the image which contains the color you want to make
transparent, then click with the left mouse button. Image
Works immediately previews the effects of the selection. To
remove all transparency, click the Clear button in the GIF
Transparency panel.